Rob Douma - Hanze

CLINICAL MUSCLE STRENGTH MEASUREMENTS: REFERENCE

VALUES AND RELIABILITY

CLINICA

L MU

SCLE STRENG

TH M

EASU

REMEN

TS; REFERENCE VALU

ES AND

RELIABILITYRob D

ouma Rob Douma

Clinical muscle strength measurements: reference

values and reliability

Rob Douma

The work presented in this thesis was performed at the Research Group Healthy

Ageing, Allied Health Care and Nursing, Hanze University of Applied Sciences,

Groningen, the Netherlands, at the Research Institute SHARE of the Groningen

Graduate School of Medical Sciences of the University Medical Center Groningen,

University of Groningen, the Netherlands.

ISBN: 978-94-6416-741-2

Photo Cover RJ

Phothographer Rob Douma

Cover Lay-out design: Publiss | www.publiss.nl

Print: Ridderprint | www.ridderprint.nl

© 2021 Rob Douma

All rights reserved. No parts of this publication may be reproduced, stored in a

retrieval system or transmitted in any form or by any means, without the prior

written permission of the copyright owner.

Clinical muscle strength measurements: reference values and reliability

Proefschrift

ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen

op gezag van de rector magnificus prof. dr. C. Wijmenga

en volgens besluit van het College voor Promoties.

De openbare verdediging zal plaatsvinden op

maandag 18 oktober 2021 om 16.15 uur

door

Rob Kornelis Wijbo Douma

geboren op 18 juli 1960 te Groningen

PromotoresProf. dr. C.P. van der SchansProf. dr. P.U. Dijkstra

CopromotorDr. W.P. Krijnen

BeoordelingscommissieProf. dr. J.M. KlaaseProf. dr. J.H.P. HoudijkProf. dr. P.J. van der Wees

ParanimfenHans van de LeurTiesja van der Woude

Contents

Chapter 1 Introduction 9

Chapter 2 Reference values for isometric muscle strength among

workers for the Netherlands: a comparison of reference

values. (2014). Douma, K. W., Soer, R., Krijnen, W. P., Reneman,

M., & C. P. van der Schans. BMC Sports Science, Medicine and

Rehabilitation, 6(1), 10. https://doi.org/10.1186/2052-1847-6-

10

27

Chapter 3 Reference values for isometric muscle strength in children

for The Netherlands between 8 and 17 years of age. Douma,

K.W., Krijnen W. P., Slager G. E. C., & van der Schans, C. P.

Submitted

49

Chapter 4 Reliability of the Q Force; a mobile instrument for measuring

isometric Quadriceps muscle strength. (2016). Douma, K.

W., Regterschot, G. R., Krijnen W. P., Slager G. E., van der

Schans, C. P., & Zijlstra, W. BMC Sports Science, Medicine and

Rehabilitation, 19(8), 4. doi:10.1186/s13102-016-0029-x

69

Chapter 5 Are repeated strength measurements required older adults.

Douma, K.W., Slager, G. E. C., Krijnen, W. P., & C. P., van der

Schans. Submitted

89

Chapter 6 Measuring Quadriceps strength in adults with severe or

moderate intellectual and visual disabilities: feasibility and

reliability. (2018). Dijkhuizen, A., Douma, K. W., Krijnen, W.

P., van der Schans, C. P., & Waninge, A. Journal of Applied

Research in Intellectual Disabilities, 31(6), 1083-1090

103

Chapter 7 General discussion 123

Summary 138

Samenvatting 144

Dankwoord 151

Institute SHARE 157

Chapter 1

Introduction

Chapter 1

10

MusclesHuman muscle anatomy has inspired human imagination since ancient Greece in

art and religion or to create myths around conquerors. In the dark ages, anatomic

illustrations and drawings were unrealistic until the 13th century when human

dissection induced considerable transformation in depicting muscle anatomy (1). Later, Michelangelo (1475-1564) created artistic work with detailed muscle

contours that currently still appeals to the imagination. It is now known that the

human body consists of more than 600 muscles which determine up to 48% of

the body weight (2,3,4). Muscles consist of a contractile part that can shorten and

tendons that generally attach to bones. Contracting and relaxing muscles are the

motors that regulate posture and movement.

Muscle strength measurementMuscle properties include length, strength, and endurance. Muscle strength is

usually measured by means of a maximal resistance test of a specific muscle

or muscle group. Muscle strength measurements are an important part of the

physical assessment in physiotherapy for which valid and reliable instruments

and their corresponding protocols are a necessity to accurately assess and

quantify maximal muscle strength. Muscle strength measurements, in general,

demonstrate a broad range of inter and intra observer reliability; reliability

coefficients range between 0.60 and 0.99 depending on the instrument that is

used (4-18). Generally, muscle strength measurements are performed utilizing one

of the following tests methods: manual resistance tests, hand-held dynamometry,

instrument-held dynamometry, isokinetic instruments, and functional tests.

Manual Resistance Testing; The Medical Research Council ScaleOne of the first attempts to develop an instrument to quantify maximal muscle

strength resulted in the Medical Research Council (MRC) scale from 0 to 5, also

known as the Oxford Scale, was developed during the second world war to

quantify maximal muscle strength of injured soldiers (19). The procedure of the

MRC scale is very understandable. During this test, the tester requests the subject

to move the arm or leg with gravity eliminated (in a horizontal plane) or against

gravity, (in a vertical plane). The movement against gravity is performed without

manual resistance or with (moderate or strong) additional manual resistance of

the tester depending on the strength of the subject who is being tested (Figure 1).

Introduction

11

1

Figure 1, Shoulder abduction test for muscle strength using the MRC Scale

Although the definitions and execution of the MRC procedures are clear, the

MRC Scale has some important inadequacies. Firstly, the grade numbers 0 to 5

suggest a continuous scale with equal differences between the numbers (Table

1). However, the numbers represent grades that are ordered points on an ordinal

scale with substantial differences between points (20).

Table 1, The 6 grades, 0 to 5, of the MRC scale

MRC Grade Muscle action

0 No contraction.

1 Flicker or trace of contraction.

2 Active movement with gravity eliminated.

3 Active movement against gravity.

4 Active movement against gravity with resistance.

5 Normal Power

MRC; Medical Research Council

These grades may lead to unjust assumptions regarding the increase or decrease

of muscle strength. For example, an increase from MRC Grade 1 to MRC Grade 2

suggests the same improvement in strength as from MRC Grade 2 to MRC Grade 3. In

reality, however, the change in actual strength may substantially differ between the

grades (20).

Secondly, the grading of the results of strength measurements is ambiguous.

Grades 0 to 3 are easy to objectify and verify and have clear cut-off points,

however, the percentage of the maximal strength that is required is not (20). For

Chapter 1

12

instance, in Grade 3, the strength required to overcome gravity varies per muscle

group between 5% for knee extension and 20% for shoulder abduction (5) (Table

2). Grade 3 can be used as an indication for being able to overcome gravity

(functional criterion), however, it provides limited information about the actual

maximal strength of a muscle group.

Table 2, Examples of percentages of maximal strength required to overcome gravity MRC Grade 3 (5)

Muscle action Percentage of maximal strength

Shoulder abduction 20%

Elbow flexion 5%

Knee extension 5%

MRC; Medical Research Council

In particular, MRC Grade 4 represents a very wide range of muscle strength. It

spans from just over Grade 3 to just below normal strength (Grade 5). In fact, for

the Biceps brachii, it encompasses approximately 95% of the total range of muscle

strength. MRC Grade 4 in this case represents approximately 5% to 99% of its

maximal strength (5,20). Due to this wide range of especially MRC Grade 4, minimal

or even moderate changes in strength cannot be distinguished.

To increase precision in Grade 4, it is further subdivided into subgrades: 4-, 4 ,

and 4+, movement against gravity with slight, moderate, and strong resistance,

respectively (21). It remains overall, however, unclear how much resistance slight,

moderate, strong manual resistance, or normal strength is in order to differentiate

between MRC Grades 4 and 5. Therefore, due to inadequate description of the

limits between Grades 4 and 5, categorizing strength appears to rely largely on

the subjective interpretation of the tester instead of the actual muscle strength.

The strength of the Biceps brachii, for example, might increase by 50% or more

without noticing it when using the MRC Scale. The above makes Grade 4 overly

inaccurate and imprecise for clinical use. Additionally, the inadequacy of manual

muscle strength measurements themselves is that the judgment slight, moderate,

or strong manual resistance or normal strength may depend on the tester’s

maximal strength. A strong tester may easily quantify low normal strength as MRC

Grade 4- whereas less strong testers could quantify it as 4, 4+, or 5 (20). When taking

the deficiencies of the MRC Scale and manual muscle testing into account, the

usefulness of the MRC Scale in clinical practice is questionable.

Introduction

13

1Hand-Held DynamometryAn instrument that overcomes some of the disadvantages of the MRC scale is the

hand-held dynamometer; the first was introduced in 1798 by Regnier (22). Various

dynamometers have been developed since then (Figure 2). The first predecessor of

today’s hand-held dynamometers was designed in the 19th century by an American

neurologist, W.A. Hammond, and was constructed by a French instrument maker,

Mathieu, in 1868 (22-25).

Figure 2, Examples of hand-held dynamometers. On the left (Figure 2) is the Collins hand-held dynamometer from the mid-19th century and, on the right is a modern hand-held dynamometer.

Currently, hand-held dynamometers are small, digital, manageable, and relatively

inexpensive devices. One of the primary advantages of the hand-held dynamometer

is that, in contrast to the MRC Scale, it quantifies the delivered maximal strength

on a linear scale with equal intervals between numbers, and it does not depend of

the interpretation of the tester. When using hand-held dynamometer instruments,

muscle strength is generally expressed in Kilogram force (Kgf), Newton (N), or

Libra Pound (LB). Measurements are executed employing isometric contractions

(contractions without movement). The device is read when the resistance

generated by the tester equals the generated maximal muscle strength by the

subject tested which is a static situation. Two types of measurements are used,

i.e., the make and the break methods. In the make method, the maximal strength

is generated by the subject whereas, in the break method, the tester attempts to

“break through” the maximal strength of the subject (20,26).

Chapter 1

14

Figure 3, Position of the hand-held dynamometer during maximal strength measurement of flexion of the elbow

The measurement procedure is relatively simple and quick, taking one to three

minutes depending on the number of repetitions. During the measurement

procedure, the subject is kept in a standardized position, for example, lying supine;

the hand dynamometer is subsequently placed perpendicular on the distal end

of the body part to be tested, for example, on the distal radius when maximal

strength of the elbow flexors is tested; the test person then flexes the arm while

it is being held back by the tester (Figure 3). Generally, a hand-held dynamometry

has good reliability coefficients ranging between 0.70 and 0.99 (6-18,27).

A hand-held dynamometry, however, has some disadvantages. For example, the

maximal strength of the testers can be a source of error (12,28,29). The tester must

be able to overcome or at least withstand the maximal strength generated by

the subject in all cases in order to ensure that the contraction is isometric. When

testers lack enough strength, measurements become non valid. (28,29). This problem

becomes more significant when subjects are stronger, however, it is less relevant

in clinical practice when they have loss of muscle strength (28,29).

Another drawback is that it is not clear if the true maximal strength is ascertained

when using a single measurement. Subjects who are not familiar with this type

of testing may need to adjust to the testing procedures and may therefore not

Introduction

15

1perform maximally during the first or second measurement. In this case, additional

measurements could lead to familiarization with the process and consequently

lead to higher values and therefore a more precise measurement of the subject’s

maximal muscle strength (30).

Instrument Held DynamometersIn addition to hand-held dynamometers, other new instruments have also been

developed in which the force sensor or dynamometer is fixed in a metal frame

incorporated in a device such as the Quadriso tester, Q Force (Figure 5) or portable

dynamometer anchoring station (DAS) (31-35). The construction of these instruments

overcomes some of the inadequacies of a hand-held dynamometry caused by

the muscle strength of the tester. These instruments are quite often “one off”

instruments and are generally not freely available. They are similar to a hand-

held dynamometry measure on a continuous scale and use static contractions.

One of the main advantages of instrument-held dynamometers is that the force

sensor is held by the device instead of a tester as in hand-held dynamometry. The

tester as a source of error is consequently reduced in these instruments. Strength,

fixation capabilities, or experience of the tester do not influence the measurement

outcome. By fixating the sensor in the instrument, the maximal range of the

measurements is increased.

Figure 4, Example of a new “instrument-held” strength measurement instrument, the Q Force

Chapter 1

16

Isokinetic instrumentsOther instruments used to measure maximal strength are isokinetic dynamometers.

“Measurements performed with isokinetic instruments are, in contrast to hand-

held and instrument-held dynamometers, executed using dynamic contractions,

and the outcomes are expressed on a linear scale in and in Newton meter (Nm).

Isokinetic dynamometers were first developed in the 1960s. Similar to hand-

held dynamometers, the force sensor is held by the instrument itself. Isokinetic

instruments are very precise measurements and can detect smaller differences

in strength than other instruments (16,36-41). The device consists of a testing chair

on which the subject is placed securely using straps. Attached to the chair is a

solid frame in which the tested arm or leg is positioned and fixed (Figure 5). The

measurement part consists of an electromotor that rotates at a constant preset

speed and only allows the tested subject to move at the same speed, resulting in a

contraction with a constant speed, i.e., an isokinetic contraction.

Figure 5, Isokinetic instrument

During the procedure, the tested subject is instructed to maximally contract

and push against the lever. The position is illustrated in Figure 5 for Quadriceps

muscle strength testing. During the procedure, the force sensor in the isokinetic

instrument quantifies the generated strength by the subject. The device provides

measurements with extensive numeric and graphic information about, among

other things, the magnitude of the strength and coordination of the contraction.

This type of instrument possesses excellent reliability and is regarded as the gold

standard for muscle strength measurement (38,41,43,44).

Introduction

17

1Functional testsHealthy older adults normally rise from a chair approximately 40 to 60 times per

day (45,46). Doing so requires adequate muscle strength (46-50). Therefore, tests that

consist of movements closely related to such activities of daily living are used to

test functional muscle strength. Functional strength tests are testing the strength

of several specific muscle groups based on frequently executed daily activities

such as reaching, walking on heels or toes, rising from a chair, or climbing stairs. In

this way, it can be determined whether loss of strength impedes a certain function

in daily life.

Functional tests are probably easier to instruct and execute than isolated strength

measurements that require isolated coordinated movements because of the

strong relationship with activities of daily life. The subject’s cooperation that is

needed for functional tests is limited to executing familiar activities of daily living.

For example, an instruction such as: “stand up from the chair as often as you can

in one minute without using your hands” will suffice. Functional strength tests

generally demonstrate good reliability (51,52,53). Specific functional strength tests,

such as the Minimum Sit-to-Stand Height Test and the 30 seconds Chair Stand Test

(30sCS), are valid and reliable tests for determining functional Quadriceps muscle

strength in a general population and older adults. (54-57).

Functional muscle strength tests provide information about the capabilities to

perform a functional movement but do not provide information about isolated

muscle strength. Therefore, when it has been established that a function is

impeded, isolated muscle strength measurements are needed to determine the

extent of loss of strength and which specific muscle groups are affected. Although

functional tests are useable in the general population as well as in older adults

and patient groups (54,56,57,58), it is not clear if these tests can reliably and validly

measure strength in individuals with, for example, (severe) intellectual or visual

disability.

Reference values for muscle strengthOutcomes of strength measurements of affected muscles groups are only

meaningful if they can be compared to reference values. Several types of reference

values are used in clinical practice. 1) The affected side is compared with the

unaffected side since minor differences are generally ascertained between the left

Chapter 1

18

and right sides in healthy individuals. 2) Follow-up measurements are compared

with baseline measurements for changes over time. 3) A subject’s strength is

compared to reference values. 4) A subject’s strength is compared with results of

prediction equations based on gender, age weight and height (6,11).

Muscle strength reference values for adults that are currently used in the

Netherlands were actually obtained in the United States. (6) However, it is not

clear if reference values for muscle strength that are drawn from a population

in a specific country can be used for other populations or in other countries. For

example, it is not evident to what extent cultural backgrounds or geographical

differences influence muscle strength of the population. For example, in 2016,

approximately 12% of Americans cycled on a regular basis whereas, in the

Netherlands, 80% did so (59,60). Exercise such as cycling has a direct and distinct

positive effect on upper leg strength and leads to greater muscle strength.

Cultural related habits or lifestyles may potentially cause differences in maximal

muscle strength between countries. Reference values this strength can partly be

predicted from height, weight, gender, and age. Height and weight are positively

related while age is negatively related to muscle strength. Females are generally

less strong than males. In the last decades, especially body weight, one of the

major predictors of maximal strength, increased considerably in the Netherlands

and the entire western society (61-64). Reference values for muscle strength used in

the Netherlands for children were generated 20 years ago (65). It seems obvious

that, if predictors of maximal muscle strength change, reference values and the

equations for estimating muscle strength reference values also change. Using

unsuitable reference values may lead to unjust clinical decisions or unobtainable

and undesirable training goals.

Objective of the thesis The general objectives of this thesis were to provide reference values for muscle

strength and to determine the reliability of different muscle strength measurement

procedures.

Chapter 2 To put a subject’s muscle strength into perspective, it must be compared with

reference values of a population with similar characteristics. Furthermore, it is

Introduction

19

1not clear whether the muscle strength of a specific population can be generalized

to another population. It is unknown if it is influenced, for example, by the

geographical location or cultural background of this population. The objective

of chapter two, therefore, was to obtain references values for the population of

Dutch workers and compare these values with those drawn from a population in

the USA.

Chapter 3 Muscle strength can be partly predicted from age, weight, and gender. Weight of

children, however, has changed over the last decades. The objective of Chapter

3, therefore, was to generate reference values for muscle strength for children

between 8 to17 years of age for the Netherlands and determine if reference

values for muscle strength for children are time specific by comparing them

with previously reported Dutch reference values. An additional objective was to

determine the degree to which muscle strength can be predicted from weight,

height, gender, and age.

Chapter 4New instruments to measure muscle strength have been developed to compensate

for inadequacies of currently used instruments. Prior to use, it must be determined

whether the reliability is acceptable to be employed in clinical practice. The

objective of Chapter 4, therefore, was to determine the test-retest reliability of the

Q Force of a new machine-held device to measure muscle strength in older adults.

Chapter 5Muscle strength measurements in clinical practice in older adults are usually

executed on one measurement day using one to three repetitions. Generally

repeated measurements lead to higher reliability but also could cause fatigue,

reducing muscle strength. It is unclear what the effects are of repeated

measurements in older adults. The objective of Chapter 5, therefore, was to

analyze effects of repeated muscle strength measurements in older adults using

a hand-held dynamometer.

Chapter 1

20

Chapter 6Functional strength testing is used in the general population and for people with

an intellectual disability. However, it is not clear if these tests can be utilized for

people with severe intellectual and visual disabilities. The objective of Chapter 6,

therefore, was to determine the feasibility, learning period, and reliability of the

Minimum Sit-to-Stand Height Test, the Leg Extension Test, and the 30 seconds

Chair-Stand Test for persons with severe intellectual and visual disabilities and to

determine the association between the scores of these tests.

Chapter 7In Chapter 7, the results of the above-mentioned studies are summarized and

put in the perspective of physiotherapy practice. The strengths and limitations of

this thesis research are summarized and discussed and suggestions are made for

further research.

Introduction

21

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Introduction

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33. Verkerke, G. J., Lemmink, K. A. P. M., Slagers, A. J., Westhoff, M. H., van Riet, G. A. J., & Rakhorst, G. (2003). Precision, comfort and mechanical performance of the Quadriso-tester, a quadriceps force measuring device. Medical and Biological Engineering and Computing, 41(3), 283–289. https://doi.org/10.1007/bf02348432

34. Ruschel, C., Haupenthal, A., Jacomel, G.F., Fontana, H.B., Santos, D.P., Scoz ,R.D., & Roesler, H. (2019). Validity and reliability of an instrumented leg-extension machine for measuring isometric muscle strength of the knee extensors. Journal of Sport Rehabilitation, 24(2), 2013-0122. https://doi.org 10.1123/jsr.2013-0122

35. Douma, K. W., Regterschot, G. R. H., Krijnen, W. P., Slager, G. E. C., van der Schans, C. P., & Zijlstra, W. (2016). Reliability of the Q Force; a mobile instrument for measuring isometric quadriceps muscle strength. BMC Sports Science, Medicine and Rehabilitation, 19 (8),1 https://doi.org/10.1186/s13102-016-0029-x

36. Deones, V. L., Wiley, S. C., & Worrell, T. (1994). Assessment of Quadriceps Muscle Performance by a Hand-Held Dynamometer and an Isokinetic Dynamometer. Journal of Orthopaedic & Sports Physical Therapy, 20(6), 296–301. https://doi.org/10.2519/jospt.1994.20.6.296

37. Valovich-mcLeod, T. C., Shultz, S. J., Gansneder, B. M., Perrin, D. H., & Drouin, J. M. (2004). Reliability and validity of the Biodex system 3 pro isokinetic dynamometer velocity, torque and position measurements. European Journal of Applied Physiology, 91(1), 22–29. https://doi.org/10.1007/s00421-003-0933-0

38. Chamorro, C., Armijo-Olivo, S., De La Fuente, C., Fuentes, J., & Javier Chirosa, L. (2017). Absolute reliability and concurrent validity of hand-held dynamometry and isokinetic dynamometry in the hip, knee and ankle joint: Systematic review and meta-analysis. Open Medicine, 12(1), 359–375. https://doi.org/10.1515/med-2017-0052

39. Reinking, M. F., Bockrath-Pugliese, K., Worrell, T., Kegerreis, R. L., Miller-Sayers, K., & Farr, J. (1996). Assessment of Quadriceps Muscle Performance by Hand-Held, Isometric, and Isokinetic Dynamometry in Patients With Knee Dysfunction. Journal of Orthopaedic & Sports Physical Therapy, 24(3), 154–159. https://doi.org/10.2519/jospt.1996.24.3.154

40. Claiborne, T. L., Timmons, M. K., & Pincivero, D. M. (2009). Test–retest reliability of cardinal plane isokinetic hip torque and EMG. Journal of Electromyography and Kinesiology, 19(5), 345–352. https://doi.org/10.1016/j.jelekin.2008.07.005

41. Stark, T., Walker, B., Phillips, J. K., Fejer, R., & Beck, R. (2011). Hand-held Dynamometry Correlation With the Gold Standard Isokinetic Dynamometry: A Systematic Review. Physical medicine & Rehabilitation, 3(5), 472–479. https://doi.org/10.1016/j.pmrj.2010.10.025

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42. Maffiuletti, N. A., Bizzini, M., Desbrosses, K., Babault, N., & Munzinger U. (2007). Reliability of knee extension and flexion measurements using the Con-Trex isokinetic dynamometer. Clinical Physiology and Functional Imaging, 27(6), 346–53. https://doi: 10.1111/j.1475-097X.2007.00758.x. PMID: 17944656.

43. Duarte, J. P., Valente-Dos-Santos, J., Coelho-E-Silva, M. J., Couto, P., Costa, D., Martinho, D., . . . Gonçalves, R. S. (2018). Reproducibility of isokinetic strength assessment of knee muscle actions in adult athletes: Torques and antagonist-agonist ratios derived at the same angle position. PloS one, 13(8), https://doi.org/10.1371/journal.pone.0202261

44. Muff, G., Dufour, S., Meyer, A., Severac, F., Favret, G. B., Lecocq, J., & Isner-Horobeti, M. E. (2016). Comparative assessment of knee extensor and flexor muscle strength measured using a hand-held vs. isokinetic dynamometer. Journal of Physical Therapy Science, 28(9), 2445–2451. https://doi.org/10.1589/jpts.28.2445

45. Bohannon, R. W., Barreca, S. R., Shove, M. E., Lambert, C., Masters, L. M., & Sigouin, C. S. (2008). Documentation of daily sit-to-stands performed by community-dwelling adults. Physiotherapy Theory and Practice, 24(6), 437–442. https://doi.org/10.1080/09593980802511813

46. Dall, P. M., & Kerr, A. (2010). Frequency of the sit to stand task: An observational study of free-living adults. Applied Ergonomics, 41(1), 58–61. https://doi.org/10.1016/j.apergo.2009.04.005

47. Bassey, E. J., Fiatarone, M. A., O’neill, E. F., Kelly, M., Evans, W. J., & Lipsitz, L. A. (1992). Leg extensor power and functional performance in very old men and women. Clinical Science, 82(3), 321–327. https://doi.org/10.1042/cs0820321

48. Brooks, S. V., & Faulkner, J. A. (1994). Skeletal muscle weakness in old age. Medicine & Science in Sports & Exercise, 26(4), 432-439. https://doi.org/10.1249/00005768-199404000-00006

49. Guralnik, J. M., Simonsick, E. M., Ferrucci, L., Glynn, R. J., Berkman, L. F., Blazer, D. G., . . . Wallace, R. B. (1994). A Short Physical Performance Battery Assessing Lower Extremity Function: Association With Self-Reported Disability and Prediction of Mortality and Nursing Home Admission. Journal of Gerontology, 49(2), 85–94. https://doi.org/10.1093/geronj/49.2.m85

50. Horlings, C. G. C., van Engelen, B. G. M., Allum, J. H. J., & Bloem, B. R. (2008). A weak balance: the contribution of muscle weakness to postural instability and falls. Nature Clinical Practice Neurology, 4(9), 504–515. https://doi.org/10.1038/ncpneuro0886

51. Tiedemann, A., Shimada, H., Sherrington, C., Murray, S., & Lord, S. (2008). The comparative ability of eight functional mobility tests for predicting falls in community dwelling older people. Age and Ageing, 37(4), 430–435. https://doi.org/10.1093/ageing/afn100

52. Bohannon, R. W. (2011). Test-Retest Reliability of the Five-Repetition Sit-to-Stand Test: A Systematic Review of the Literature Involving Adults. Journal of Strength & Conditioning Research, 25(11), 3205–3207. https://doi.org/10.1519/JSC.0b013e318234e59f

53. Luque-Siles, C., Gallego-Izquierdo, T., Jímenez-Rejano, J. J., de-la-Orden, S. G., Plaza-Manzano, G., López-Illescas-Ruizx, . . . Pecos-Martín, D. (2016). Reliability and minimal detectable change of three functional tests: Journal of Physical Therapy Science, 28(12), 3384–3389. https://doi.org/10.1589/jpts.28.3384

Introduction

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154. Jones, C. J., Rikli, R. E., & Beam, W. C. (1999). A 30-s Chair-Stand Test as a Measure of Lower Body Strength in Community-Residing Older Adults. Research Quarterly for Exercise and Sport, 70(2), 113–119. https://doi.org/10.1080/02701367.1999.10608028

55. Rikli, R. E., & Jones, C.J., Senior fitness test manual. (2002). Choice Reviews Online, 39(06), 39–3447. https://doi.org/10.5860/choice.39-3447

56. Rikli, R. E., & Jones, C. J. (1999). Development and Validation of a Functional Fitness Test for Community-Residing Older Adults. Journal of Aging and Physical Activity, 7(2), 129–161. https://doi.org/10.1123/japa.7.2.129

57. Schurr, K., Sherrington, C., Wallbank, G., Pamphlett, P., & Olivetti, L. (2012). The minimum sit-to-stand height test: reliability, responsiveness and relationship to leg muscle strength. Clinical Rehabilitation, 26(7), 656–663. https://doi.org/10.1177/0269215511427323

58. Bohannon, R. W., Bubela, D. J., Magasi, S. R., & Gershon, R. C. (2011). Relative reliability of three objective tests of limb muscle strength. Isokinetics and Exercise Science, 19(2), 77–81. https://doi.org/10.3233/ies-2011-0400

59. Es, M., & Slütter, M. (2019, 24 April). Fietsen in cijfers. Fietsersbond. https://www.fietsersbond.nl/ons-werk/mobiliteit/fietsen-cijfers/

60. Lange, D. (2020, 3 December). Cycling - Statistics & Facts. Statista. https://www.statista.com/topics/1686/cycling/

61. National Institute of Diabetes and Digestive and Kidney Diseases. (2021, 11 January). Overweight & Obesity Statistics. https://www.niddk.nih.gov/health-information/health-statistics/overweight-obesity#prevalence

62. Hales, C. M. (2017, 1 Oktober). Prevalence of obesity among adults and youth: United States, 2015–2016. Welcome to CDC Stacks. https://stacks.cdc.gov/view/cdc/49223

63. Carreira, H., Pereira, M., Azevedo, A., & Lunet, N. (2012). Trends of BMI and prevalence of overweight and obesity in Portugal (1995–2005): A systematic review. Public health Nurse, 15(6), 972-981. doi:10.1017/S1368980012000559

64. Schönbeck, Y., Talma, H., van Dommelen, P., Bakker, B., Buitendijk, S. E., HiraSing, R. A., & van Buuren, S. (2011). Increase in Prevalence of Overweight in Dutch Children and Adolescents: A Comparison of Nationwide Growth Studies in 1980, 1997 and 2009. PLoS ONE, 6(11), e27608. https://doi.org/10.1371/journal.pone.0027608

65. Beenakker, E. A. C., van der Hoeven, J. H., Fock, J. M., & Maurits, N. M. (2001). Reference values of maximum isometric muscle force obtained in 270 children aged 4–16 years by hand-held dynamometry. Neuromuscular Disorders, 11(5), 441–446. https://doi.org/10.1016/s0960-8966(01)00193-6

Chapter 2

Reference values for isometric muscle strength among workers for

the Netherlands: a comparison of reference values

Douma, K. W., Soer, R., Krijnen, W. P., Reneman, M., & C. P. van der Schans. (2014). BMC Sports Science, Medicine and Rehabilitation, 6,(1), 10.

https://doi.org/10.1186/2052-1847-6-10

Chapter 2

28

AbstractBackground Muscle strength is important for daily life and sports and can be

measured with a hand-held dynamometer. Reference values are employed to

quantify a subject’s muscle strength. It is unclear whether reference values can

be generalized to other populations. Objectives in this study were; first to confirm

reliability of the utilization of hand-held dynamometers for isometric strength

measurement; second to determine reference values for a population of Dutch

workers; third to compare these values with those of a USA population.

Methods 462 Healthy working subjects (259 male, 203 female) were included in

this study. Their age ranged from 20 to 60 years with a mean ( SD) of 41 (11)

years. Muscle strength values from elbow flexion and extension, knee flexion and

extension, and shoulder abduction were measured with the break method using

a MicroFet 2 hand-held dynamometer. Reliability was analyzed by calculating

ICC’s and limits of agreement. Muscle strength expressed in Newton, means,

and confidence intervals were determined for males and females in age groups

ranging from twenty to sixty years old. Regression equations and explained

variances were calculated from weight, height, age, and gender. The mean values

and 95% CI were compared to the results from other studies.

Results Reliability was good; the ICCs ranged between 0.83 to 0.94. The explained

variance of the regression equations ranged from 0.25 to 0.51. Comparison of

data for the Dutch population mean muscle strength values with those from the

USA revealed important differences between muscle strength reference values for

the American and Dutch populations.

Conclusions Muscle strength measurements demonstrate a sound reliability.

Reference values and regressions equations are made available for the Dutch

population. Comparison with other studies indicates that reference values differ

between countries.

Reference values for isometric muscle strength among workers for the Netherlands

29

2

BackgroundMuscle strength is considered to be an important determinant for physical

performance, activities of daily living, and work or sport performance (1). Several

processes such as aging, development of pathological symptoms, or injury may

result in reduced muscle strength. Muscle strength can be quantified by several

viable instruments.

Precise measurements are feasible by employing hand-held dynamometers, which

allows muscle strength to be measured on a continuous scale. Several authors

have demonstrated in various settings that hand-held dynamometry is reliable

and the data valid for quantifying muscle strength. They ascertained an intraclass

correlation coefficient (ICC) of 0.8 or higher, indicating good sound reliability (2-11).

However, precise and reliable measurement outcomes are only meaningful if they

can be compared with unaffected muscle groups or, more precisely, with reference

values. For example, chronically ill patients may exhibit a bilateral decrease of

muscle strength, illustrating that the extent of the decline in a specific patient can

only be quantified if measured muscle strength values are compared with objective

reference values (8). However reference values are employed in generally every

type of physical examination and are often generated for a specific population.

For example, for six minutes walking or pulmonary function tests, reference

values are based on a population’s particular origin, and outcomes demonstrate

considerable mutual differences (10,11). Muscle strength values, however, are utilized

without taking into consideration ethnic, geographic, or cultural background. Until

now, reference values used in clinical practice and in research in the Netherlands

are based on populations in the USA. The consideration is justified if reference

values for the American population can be generalized to the Dutch population.

However, geographical location and cultural backgrounds vary considerably and,

therefore, this generalization may not be credible.

The first objective of this study was to confirm the reliability of the use of hand-

held dynamometers for isometric strength measurement; the second objective

was to determine references values for a population of Dutch workers; the third

objective was to compare these values with those of the USA population presented

in studies by Bohannon and Andrews (3,9). Comparison between reference values

for muscle strength has not been performed previously.

Chapter 2

30

MethodsDesignCross sectional study

SubjectsThe subjects were recruited via local press from different regions in the

Netherlands and had been employed in several fields, and had miscellaneous

physical workloads.

Inclusion criteria: Subjects had to be between 20 and 60 years of age and working

at least 20 hours per week. No absence from work due to illness for more than

2 weeks in the year prior to participation. Subjects were included after providing

informed consent and signing a statement of good health after meeting the criteria

of the Physical Activity Readiness Questionnaire (12,13). Exclusion criteria: Subjects

were excluded if systolic and diastolic blood pressures exceeded 159 mmHg and

100 mmHg, respectively, as described by the WHO, to prevent cardiovascular

injury (14), were absent from work in the last year as a result of a musculoskeletal

disorder, or presented co-morbidities relating to either the cardiovascular or

respiratory systems or otherwise did not meet the inclusion criteria. The Medical

Ethics Committee of the University Medical Center Groningen, the Netherlands,

approved the study protocol (METc 2005/198).

Measurement procedureThe subjects’ gender, age, hand dominance, height, weight, physical activity, and

Dictionary of Occupational Titles (DOT) level were recorded (15). The DOT level

describes the difficulty of comprehending, nature, tasks of specific types of work,

or specified occupational titles. The DOT is meant to match job requirements

and employees’ functional abilities and consists of five categories: sedentary,

light, medium, heavy, and very heavy. Maximal isometric voluntary contraction

(MVC) was measured with a MicroFet 2 hand-held dynamometer (Hogan Health

Industries, Inc. 8020 South 1300 West, West Jordan, USA). Three consecutive

measurements were performed with one minute intervals between contractions.

Isometric muscle strength from elbow flexion and extension, knee flexion and

extension, and shoulder abduction were measured. The protocol consisted of


31

2

one contraction for every individual muscle in the following sequence; 1 elbow

flexion, 2 elbow extension, 3 knee extension, 4 knee flexion, and 5 shoulder

abduction. This sequence was performed three times. Observers were allowed to

begin left or right according to their preference. Subjects were asked to gradually

increase their muscle strength to a maximum effort which would need to be

sustained for three seconds. The ‘break technique’ was employed whereby the

examiner overpowers the maximum effort of the patient, thereby producing a

measurement of eccentric muscle strength (16,17). The average muscle strength of

three repetitions was calculated to compensate for and minimize measurement

errors. Subjects were assessed by third or fourth year physiotherapy students

from the Hanze University of Applied Sciences Groningen, the Netherlands. An

experienced instructor trained the students prior to the tests. Students were

instructed to perform the break technique in the following manner. First, they

were instructed to ‘break through’ the subject’s muscle strength by countering

the strength employing a continuous, slow movement. Second, they were to

maintain their position and the patient’s position throughout the entire test.

Observers provided standardized encouragement. In the event that the observer

was unable to break through the patient’s generated strength, this was recorded

in the administration form, and that result was omitted from the data analysis.

Measurements were taken in a standardized and gravity neutral body position.

Measurement positions are described in Table 1 (Figures 1, 2 and 3).

Chapter 2

32

Tabl

e 1,

Des

crip

tion

of b

ody

posi

tions

dur

ing

mea

sure

me

Mus

cle

stre

ngth

/M

ovem

ent

Join

t/Li

mb

posi

tion

Loca

lizat

ion

HH

DPo

siti

on s

ubje

ctFi

xati

on s

ubje

ctPo

siti

on/F

ixat

ion

obse

rver

Elbo

w fl

exio

nN

eutr

al s

houl

der,

elbo

w fl

exed

90º

; up

per

arm

aga

inst

tr

unk

Just

pro

xim

al to

sty

loid

pr

oces

s of

rad

ius

Lyin

g su

pine

By b

ody

wei

ght;

feet

aga

inst

wal

lAl

ongs

ide

the

tabl

e an

d te

st s

ubje

ct,

lean

ing

back

war

d

Elbo

w e

xten

sion

Sam

e as

in fl

exio

nJu

st p

roxi

mal

to u

lnar

hea

dSa

me

as in

fle

xion

Sam

e as

in

flexi

onSa

me

as in

flex

ion

Knee

flex

ion

Hip

and

kne

e fle

xed

90º

Just

pro

xim

al to

cal

cane

usSi

ttin

g on

tabl

eBy

bod

y w

eigh

t an

d ac

tive

fixat

ion

whi

le

grip

ping

tabl

e

In fr

ont o

f tes

t sub

ject

; fe

et fi

xed

onto

tabl

e

Knee

ext

ensi

onSa

me

as in

flex

ion

Just

pro

xim

al to

talu

sSa

me

as in

fle

xion

By b

ody

wei

ght

and

activ

e fix

atio

n.

In fr

ont o

f tes

t sub

ject

; fix

ated

by

body

w

eigh

t, gr

ippi

ng ta

ble,

an

d pu

shin

g fo

rwar

d;

HH

D fi

xatio

n ag

ains

t up

per

leg

Shou

lder

abd

ucti

on90

º abd

uctio

n in

sh

ould

erJu

st p

roxi

mal

to la

tera

l ep

icon

dyle

Sitt

ing

on

exam

inat

ion

tabl

e or

cha

ir

Body

wei

ght

Behi

nd s

ubje

ct

HH

D, H

and-

held

dyn

amom

eter

.


33

2

Figure 1, Positions hand-held dynamometer. (a) elbow flexion, (b) elbow extension

Figure 2, Positions hand-held dynamometer. (a) Knee extension, (b) Knee flexion

Figure 3, Position hand-held dynamometer shoulder abduction.

Chapter 2

34

Statistical analysesAll data were analyzed with SPSS 14.0. To answer the primary objective of this study,

reliability of the three repeated measurements, the intraclass correlation coefficients

(ICC) two-way random effects model including lower and upper 95% confidence limits

(LCL and UCL), as well as the limits of agreement (LOA) were calculated (18). Limits of

agreement were collectively calculated for males and females and encompassing all

age groups and for each pair of repeated measurements [19]. ICCs were interpreted

as follows: ICC < 0.25 is low reliability; 0.25 < ICC < 50 moderate reliability; 50 < ICC <

75 good reliability and ICC > 0.75 is excellent reliability (19-21).

To address the second objective, reference values for muscle strength were

constructed by calculating means and standard deviations. Results were stratified

by age groups and gender. Differences between males and females were analyzed

utilizing independent samples t-tests. To investigate the degree to which muscle

strength is linearly related to, gender, weight, height and age, a linear regression

analysis was performed and the explained variance, (R2) was calculated. To answer

the third objective, comparisons between muscle strength outcomes of the

current study and two different studies, was performed by comparing the means

of the two other studies with our means and 95% confidence intervals (95% CI) (3,9) .

Results

SubjectsA sample of 462 healthy subjects (259 males and 203 females) was included in this study.

The subject and group characteristics are presented in Table 2.

ReliabilityCorrelations between the three measurements varied between 0.83 and 0.94, ICC

values varied between 0.83 and 0.92 and are presented in Table 3. Since the 95%

confidence intervals were small, it is relatively certain that the population values of

the coefficients are similar to the estimated values (17,19,21). All ICC values were higher

than 0.75, indicating good reproducibility for all ten muscle measurements (19,21).

The limits of agreement varied between 37.0 and 117.8 Newton. Elbow extension

left demonstrated a narrow 95% CI while knee extension right demonstrated a

wide 95% CI.


35

2

Tabl

e 2,

Cha

ract

eris

tics

of th

e po

pula

tion

stra

tified

by

age

grou

p an

d ge

nder

Mal

e

Age

grou

p20

-59

20-2

930

-39

40-4

950

-59

Age

41.7

(11)

25.2

(3)

33.6

(3)

44.9

(3)

54.1

(3)

Hei

ght

182.

1(8)

182.

0(8)

181.

4.6(

8)18

3.5(

8)18

1.2(

7)

Wei

ght

80.8

(12)

74.3

(10)

80.6

(13)

82.4

(10)

82.4

(14)

BMI

24.4

(4)

22.4

(3)

24.4

(4)

24.4

(3)

25.1

(4)

DO

T 1

18.9

10.0

22.0

25.4

15.4

DO

T 2

44.3

33.3

24.3

46.0

60.0

DO

T 3

22.9

43.3

34.1

12.7

16.9

DO

T 4

13.9

13.3

19.5

15.9

7.7

Fem

ale

Age

grou

p20

-59

20-2

930

-39

40-4

950

-59

Age

40.2

(10)

25.9

(3)

34.8

(3)

44.3

(3)

53.6

(3)

Hei

ght

170.

1(7)

172.

5(6)

170.

8(8)

170.

0(7)

167.

4(7)

Wei

ght

68.0

(11)

68.1

(13)

68.2

(9)

68.0

(11)

67.8

(12)

BMI

23.4

(3)

22.9

(4)

23.5

(3)

23.4

(3)

24.1

(4)

DO

T 1

21.2

14.0

21.1

12.7

43.6

DO

T 2

42.5

41.

933

.454

.033

.3

DO

T 3

35.3

44.2

45.5

30.2

23.1

DO

T 4

10

03.

10

Age,

Hei

ght,

Wei

ght a

nd B

MI e

xpre

ssed

in m

ean(

SD

) and

DO

T is

exp

ress

ed in

per

cent

age

of th

e po

pula

tion.

DO

T; D

ictio

nary

of O

ccup

atio

nal T

itles

. DO

T 1

= se

dent

ary,

DO

T 2

= lig

ht, D

OT

3 =

med

ium

, DO

T 4

= he

avy/

very

hea

vy.

Chapter 2

36

Table 3, Correlation between the three measurements, intraclass correlation coefficient, and limits of agreement for three repeated measurements

Muscle strength

Corr1-2

Corr1-3

Corr2-3

ICC LCL- UCL LOA1-2 LOA1-3 LOA2-3

Elbow flex. left 0.88 0.87 0.87 0.87 0.85 - 0.89

± 59.4 ± 61.6 ±61.0

Elbow flex. right

0.85 0.86 0.89 0.87 0.85 - 0.89

± 67.8 ± 66.8 ± 56.3

Elbow ext. left 0.89 0.85 0.88 0.88 0.86 - 0.89

± 42.8 ± 50.3 ±44.1

Elbow ext. right

0.91 0.91 0.93 0.92 0.90 - 0.93

± 37.0 ± 37.2 ±32.9

Knee flex. left 0.83 0.81 0.87 0.84 0.81 - 0.86

± 75.9 ± 82.5 ±68.8

Knee flex. right

0.87 0.82 0.88 0.86 0.83 - 0.88

± 69.8 ± 81.4 ±67.8

Knee ext. left 0.88 0.85 0.91 0.88 0.86 - 0.89

± 104.0 ±117.8 ±94.3

Knee ext. right.

0.91 0.90 0.94 0.92 0.90 - 0.93

± 96.3 ± 106.7 ± 80.2

Abduction left 0.83 0.80 0.87 0.83 0.80 - 0.86

± 55.2 ± 59.5 ±48.4

Abduction right

0.85 0.87 0.92 0.88 0.85 - 0.90

± 52.6 ± 46.5 ±37.3

Corr: Correlation, ICC: intraclass correlation coefficient, LCL: lower 95% confidence limit, UCL: upper 95% confidence limit, LOA: limits of agreement.

Reference valuesTables 4 and 5 illustrate the mean muscle strength values for reference values

from elbow flexion and extension, knee flexion and extension, and shoulder

abduction stratified by age groups, gender, and dominance. Regression equations

and explained variance are presented in Table 6. The explained variance varied

between 0.25 for knee extension right and 0.51 for elbow extension left.


37

2

Tabl

e 4

Dom

inan

t and

non

-dom

inan

t mus

cle

stre

ngth

mea

ns (S

D) p

er a

ge g

roup

for m

ales

Mal

eD

omin

ant

Non

dom

inan

t

Mus

cle

stre

ngth

Age

gro

upN

Mea

n(SD

) N

Mea

n (S

D)

Elbo

w fl

exio

n20

-29

4828

1(48

)48

261(

49)

30-3

951

273(

50)

5126

6(51

)

40-4

970

271(

59)

7026

1(51

)

50-5

959

259(

52)

5924

5(47

)

Elbo

w e

xten

sion

20-2

948

186(

38)

4818

2(37

)

30-3

951

183(

40)

5117

9(45

)

40-4

970

185(

46)

7017

9(44

)

50-5

959

181(

37)

5917

3(36

)

Knee

flex

ion

20-2

948

267(

57)

4825

2(52

)

30-3

951

262(

60)

5125

0(55

)

40-4

968

274(

77)

6926

3(77

)

50-5

959

242(

57)

5923

4(55

)

Knee

ext

ensi

on20

-29

47 3

79(1

05)

47 3

71(1

12)

30-3

951

351(

99)

51 3

41(1

01)

40-4

969

368

(114

)70

341

(107

)

50-5

959

337

(103

)57

335

(102

)

Scho

ulde

r ab

duct

ion

20-2

914

172(

48)

1417

3(35

)

30-3

926

181(

38)

2617

6(40

)

40-4

935

173(

43)

3517

7(40

)

50-5

937

178(

39)

3917

7(43

)

SD: s

tand

ard

devi

atio

n.

Chapter 2

38

Tabl

e 5,

Dom

inan

t and

non

-dom

inan

t mus

cle

stre

ngth

mea

ns (S

D) p

er a

ge g

roup

for f

emal

es

Fem

ale

Dom

inan

tN

on d

omin

ant

Mus

cle

stre

ngth

Age

gro

upN

Mea

n(SD

)N

Mea

n(SD

)

Elbo

w fl

exio

n20

-29

5119

1(30

)51

183(

30)

30-3

939

195(

34)

3918

6(35

)

40-4

966

191(

37)

6618

6(37

)

50-5

934

181(

29)

3416

6(22

)

Elbo

w e

xten

sion

20-2

951

132(

28)

5113

1(28

)

30-3

939

128(

24)

3912

5(26

)

40-4

966

131(

28)

6612

5(29

)

50-5

934

120(

20)

3411

8(27

)

Knee

flex

ion

20-2

951

198(

38)

5119

1(37

)

30-3

939

190(

41)

3918

8(35

)

40-4

966

190(

51)

6718

3(52

)

50-5

934

174(

42)

3416

9(45

)

Knee

ext

ensi

on20

-29

5126

1(80

)51

260(

75)

30-3

938

273(

87)

3926

4(88

)

40-4

966

262

(127

)67

245(

79)

50-5

934

244(

66)

3422

8(51

)

Scho

ulde

r ab

duct

ion

20-2

914

115(

19)

1412

4(23

)

30-3

922

116(

26)

2211

8(30

)

40-4

941

119(

28)

4111

8(26

)

50-5

915

114(

22)

1511

6(21

)

SD: s

tand

ard

devi

atio

n.

Tabl

e 6,

Reg

ress

ion

equa

tions

for c

alcu

latio

n of

refe

renc

e va

lues


39

2

Muscle strength Regression equations R2

Elbow flex. left -4.93+56.96*S - 0.64*A +0.89*W +0,89*H 0.51

Elbow flex. right 10.67+57.47*S -0.72*A +0.95*W +0.85*H 0.49

Elbow flex. left 23.85+36.56*S -0.50*A +1.07*W +0.29*H 0.44

Elbow flex. right 80.39+41.56*S -0.47*A +0.14*W +0.06*H 0.48

Knee flex. left 47.92+43.52*S -0.60*A +1.36*W +0.40*H 0.34

Knee flex. right 43.84+47.03*S -0.71*A +1.33*W +0.50*H 0.35

Knee ext. left -204.36+43.96*S -1.13*A +1.90*W +2.19*H 0.31

Knee ext. right -215.54+40.73*S -0.82*A +2.0*W +2.22*H 0.25

Shoulder abd. left -20.86+45.25*S -0.004*A +0.64*W +0.56*H 0.46

Shoulder abd. right 10.07+43.63*S -0.16*A +0.76*W +0.36*H 0.34

S, sex (1 for male, 0 for female); A, age; W, weight; H, height.

ComparisonMean muscle strength values and the 95% CI from the current study and mean

muscle strength values from studies by Bohannon and Andrews are presented in

Tables 7 and 8. Comparison of Dutch mean muscle strength values to those from

Bohannon and Andrews (3,9) revealed that a significant difference existed between

reference muscle strength values between different populations.

Chapter 2

40

Tabl

e 7,

Com

paris

on b

etw

een

the

curr

ent s

tudy

and

stu

dies

of B

ohan

non

(3) a

nd A

ndre

ws

(9) f

or m

ale

Mal

eD

omin

ant

Non

dom

inan

tM

uscl

e st

reng

thCu

rren

t st

udy

Boha

nnon

And

rew

sCu

rren

t st

udy

Boha

nnon

And

rew

s

Mea

n (9

5% C

I)M

ean

Mea

nM

ean

(95%

CI)

Mea

nM

ean

Elbo

w fl

exio

n

A

ge g

roup

20-

2928

1 (2

67-2

95)

285

-26

1 (2

47-2

76)

279

-

3

0-39

273

(259

-287

)26

9-

266

(252

-281

)28

1-

40-

4927

1 (2

58-2

86)

269

-26

1 (2

49-2

74)

270

-

5

0-59

259

(246

-272

)28

729

224

5 (2

32-2

57)

268

272

Elbo

w e

xten

sion

Age

gro

up

2

0-29

186

(175

-197

)24

4-

182

(171

-194

)24

5-

30-

3918

5 (1

72-1

94)

214

-17

9 (1

67-1

92)

231

-

4

0-49

185

(174

-196

)21

0-

179

(169

-190

)21

4-

50-

5918

1 (1

71-1

90)

197

188

173

(164

-182

)18

617

8Kn

ee e

xten

sion

Age

gro

up

2

0-29

379

(348

-409

)57

5-

371

(339

-404

)57

9-

30-

3935

1 (3

23-3

78)

573

-34

1 (3

12-3

69)

572

-

4

0-49

368

(341

-395

)58

3-

341

(315

-366

)58

9-

50-

5933

7 (3

10-3

63)

471

448

335

(308

-362

)46

843

9Sh

ould

er a

bduc

tion

Age

gro

up

2

0-29

172

(144

-200

)25

8-

173

(152

-193

)24

6-

30-

3918

1 (1

65-1

96)

249

-17

6 (1

59-1

92)

237

-

4

0-49

173

(158

-188

)24

6-

177

(163

-191

)24

4-

50-

5917

8 (1

65-1

91)

240

238

177

(163

-191

)22

322

2

Bold

pri

nted

num

bers

are

val

ues

outs

ide

the

95%

CI o

f thi

s st

udy.

Age

grou

ps a

re g

iven

in d

ecad

es in

yea

rs, M

uscl

e st

reng

th is

giv

en in

New

ton.


41

2

Tabl

e 8,

Com

pari

son

betw

een

the

pres

ent s

tudy

and

stu

dies

of B

ohan

non

(3) a

nd A

ndre

ws

(9) f

or fe

mal

e

Fem

ale

Dom

inan

tN

on d

omin

ant

Mus

cle

stre

ngth

Curr

ent

stud

yBo

hann

onA

ndre

ws

Curr

ent

stud

yBo

hann

onA

ndre

ws

Mea

n (9

5% C

I)M

ean

Mea

nM

ean

(95%

CI)

Mea

nM

ean

Elbo

w fl

exio

n

Age

gro

up

20-

2919

1 (1

82-1

99)

155

-18

3 (1

75-1

92)

151

-

30-

3919

5 (1

84-2

06)

164

-18

6 (1

75-1

98)

161

-

40-

4919

1 (1

82-1

99)

151

-18

6 (1

76-1

95)

157

-

50-

5918

1 (1

71-1

91)

155

167

166

(158

-174

)15

616

0

Elbo

w e

xten

sion

Age

gro

up

20-

2913

2 (1

24-1

39)

116

-13

1 (1

23-1

39)

115

-

3

0-39

128

(121

-135

)11

7-

125

(116

-133

)11

9-

40-

4913

1 (1

24-1

37)

110

-12

5 (1

18-1

32)

112

-

50-

5912

0 (1

13-1

27)

111

108

118

(109

-127

)10

710

4

Knee

ext

ensi

on

Age

grou

p

2

0-29

261

(234

-288

)46

7-

260

(238

-281

)46

6-

30-

3927

3 (2

44-3

02)

408

-26

4 (2

35-2

92)

411

-

4

0-49

262

(231

-293

)38

1-

245

(225

-265

)36

3-

50-

5924

4 (2

21-2

67)

335

298

230

(210

-246

)31

929

3Sh

ould

er a

bduc

tion

Age

grou

p

20-

2911

5 (1

04-1

27)

153

-12

4 (1

10-1

37)

135

-

3

0-39

116

(105

-128

)13

9-

118

(104

-131

)13

6-

40-

4911

9 (1

10-1

28)

139

-11

8 (1

09-1

26)

129

-

5

0-59

114

(110

-128

)13

713

511

6 (1

04-1

28)

135

124

Bold

prin

ted

num

bers

are

val

ues

outs

ide

the

95%

CI o

f thi

s st

udy.

Age

gro

ups

are

give

n in

dec

ades

in y

ears

, Mus

cle

stre

ngth

is g

iven

in N

ewto

n.

Chapter 2

42

Comparison indicates that, for males, mean muscle strength values of Bohannon

and Andrews were greater than those of the current study except for elbow

flexion of the dominant and non-dominant sides in which only the age group 50–

59 years exhibited greater values. For females, mean muscle strength values of

Bohannon and Andrews were lower for elbow flexion and extension than those

in the present study with the exception of elbow extension, non-dominant for age

group 30 to 39 (Bohannon) and 50 to 59 (Andrews) years. Shoulder abduction and

knee flexion and extension indicated greater values in the study of Bohannon and

Andrews, except for shoulder abduction of the non-dominant side with age group

20 to 29 years.

DiscussionReliability of muscle strength measurements with a hand-held dynamometer is

good to excellent. All ICC values exceeded 0.80, indicating good reliability for all

ten muscle measurements. These findings corroborate with those of Bohannon (5). Reference values for muscle strength for the Dutch working population

between 20 and 60 years of age are now made available. Reference values based

on age gender, weight and height can be calculated using regression equations.

Comparison of the Dutch mean muscle strength values to those published by

Bohannon and Andrews revealed significant differences between reference

values for muscle strength values between the assessed populations. Comparison

of reference values between populations have not been initiated previously.

Muscle strength measurements with a hand-held dynamometer exhibited a good

reliability as demonstrated by the ICCs. The LOA, however, vary substantially.

Muscle groups with a relatively low muscle strength demonstrated a small

range of the LOA while muscle with a greater muscle strength demonstrated a

larger range of the LOA, indicating that measurements of stronger muscles are

less precise. Though hand-held dynamometers have shown to be a reliable and

beneficial instrument for measuring muscle strength, a hand-held dynamometer

may possess some practical limitations. In subjects with high Quadriceps muscle

strength, it might be impossible to perform a correct measurement (12). During our

study, it was not possible to perform a correct measurement of the Quadriceps

muscle in six subjects due to high muscle strength as observers were not capable

of performing a correct break procedure. As reliability and validity may be affected


43

2

during these measurements, bias was likely present, which is the reason that

these results were omitted from the analysis. The influence of exclusion of these

data on reliability, regression formulas, and reference values is very limited due

to the considerable sample size. Provided that observers were able to properly

perform according to the protocol, the regressions formula for knee extension

might be only slightly changed. In our opinion, a hand-held dynamometer is

not suitable for measuring Quadriceps muscle strength in stronger subjects.

Reference values for muscle strength for the Dutch working population between

the ages of 20 and 60 years are now made available. Regression equations illustrate

that gender, weight, and height are of major influence on muscle strength.

The effect of age, however, is limited. In several of the regression analyses, the

effect of age was small, though significant, due to the considerable sample size.

Regression analysis demonstrated that the effect of aging for subjects aged 20–

60 years is larger for lower extremities than for upper extremities. These results

are predominantly consistent with previously reported results (3,9). Bohannon and

Andrews also reported that gender, age, height, and weight were predictors of

muscle strength and that age correlated significantly, though very limited, with

muscle strength. Comparison of the outcomes of our study to those earlier

exhibited an important difference between reference values. The differences in

upper extremity tests, however, were moderate in all cases, whereas most of

the lower extremity differences were considerable. For instance, differences in

muscle strength greater than 100 Newton for knee extension may have clinical

consequences as 100 Newton’s may be up to 42 percent of the maximum knee

extension strength in the Dutch female population. The observed differences,

however, exceed 100 Newton. This difference is all the more remarkable because,

in our study, we employed the break method while, in the studies of Bohannon

and Andrews, the make method was used. The break method leads to higher

levels in muscle strength measurements (16). The observed differences in the lower

extremity are relevant for clinical practice. These differences may probably cause

unattainable and/or undesirable training goals to be set and may result in undesired

side effects as these external reference values may be too high and, therefore,

not suitable for the Dutch population. However, reference values formulated for

the United States are, at this moment, utilized in clinical practice and research

in the Netherlands. The results of our study demonstrate that reference values

cannot simply be generalized to any country, geographical area, or population.

Chapter 2

44

Therefore, it is necessary to generate reference values for different countries or

geographical areas. For other physiological tests such as the six minutes walking

test reference values for specific geographic reference values are available and

indicate considerable differences (9). Although we did not assess cultural habits

or demographic aspects of populations, it is likely that the outcomes of muscle

strength measurements may be influenced by several such factors. Psychological

state or prior experiences related to exertion or physiological responses to

exercise, exertion, or pain might have influenced the outcomes (21) In addition,

body composition and weight are related to muscle strength as presented in the

regression equations. Another potential explanation for the differences between

our reference values and those previously reported by Andrews and Bohannon

is the difference in time periods. The reference values of Andrews and Bohannon

were determined in 1988 and ours in 2010. In approximately 20 years, some

characteristics such as BMI or physical activity level may have changed which may

affect references values.

Study limitationsIn our study, we tested the employed working population between the ages

of 20 and 60 years. Our study, therefore, only provides reference values and

comparisons for this group. Our study does not provide information regarding, for

example, unemployed businessmen or housekeepers. Another limitation in our

study is that observers were male and female. We did not register whether subjects

were tested by male or female observers. The outcomes of measurements may

be biased by the gender of the observer. Reliable muscle strength measurements,

appropriate and applicable reference values, and accurate knowledge of acquired

muscle strength in daily living facilitates formulating an effective and accurate

rehabilitation process with clear and realistic goals and objective effects. Although

reliable measurements of a person’s muscle strength are beneficial, no valid

procedures are currently available for translating isometric contractions or

reference values, for that matter, into function. Functional tests probably provide

an improved reflection of a subject’s functional muscle strength, capacity, or ability

for activities of daily living or work. Therefore the role of muscle strength should

be interpreted with caution and that other variables may also influence activities

of daily living. Additional studies are needed to define the specific role and the

amount of muscle strength required in activities of daily living.


45

2

ConclusionsMeasuring muscle strength by dynamometry is reliable and suitable for clinical

practice. Substantial differences exist for reference muscle strength values

between different populations. Reference values are specific for different regions

and cannot simply be generalized to other populations.

Chapter 2

46

References1. Morris, M. G., Dawes, H., Howells, K., Scot, O. M., & Cramp, M. (2008). Relationship

between muscle fatigue characteristics and markers of endurance performance. Journal of Sports Science and Medicine, 7(4), 31–436. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3761932/



4. Bohannon R.W., & Andrews A.,W. (1987). Interrater reliability of hand-held dynamometry. Physical Therapy, 67(6), 931–933. https://doi.org/10.1093/ptj/67.6.931


6. Wang, C.Y., Olson, S. L., & Protas, E. J. (2002). Test-retest strength reliability: Hand-held dynamometry in community-dwelling elderly fallers. Archives of Physical Medicine and Rehabilitation, 83(6), 811–815. https://doi.org/10.1053/apmr.2002.32743

7. Roy, M. A. G., & Doherty, T. J. (2004). Reliability of Hand-Held Dynamometry in Assessment of Knee Extensor Strength After Hip Fracture. American Journal of Physical Medicine & Rehabilitation, 83(11), 813–818. https://doi.org/10.1097/01.phm.0000143405.17932.78

8. Bohannon, R. W. (1997). Discriminant Construct Validity of Hand-Held Dynamometry and Manual Muscle Testing in a Home Care Setting. Journal of Physical Therapy Science, 9(2), 57–61. https://doi.org/10.1589/jpts.9.57


10. Vaish, H., Ahmed, F., Singla, R., & Shukla, D. K. (2013). Reference equation for the 6-minute walk test in healthy North Indian adult males. The International Journal of Tuberculosis and Lung Disease, 17(5), 698–703. https://doi.org/10.5588/ijtld.12.0474

11. Fulambarker, A., Copur, A. S., Javeri, A., Jere, S., & Cohen, M. E. (2004). Reference Values for Pulmonary Function in Asian Indians Living in the United States. Chest, 126(4), 1225–1233. https://doi.org/10.1378/chest.126.4.1225

12. Conference on physical activity, fitness and health (1978). PAR-Q Validation Report. In British Columbia Ministry of Health, Champaign, IL: Human Kinetics.

13. Thomas, S., Reading, J., & Shephard, R. J. (1992). Revision of the physical activity readiness questionnaire (PAR-Q). Canadian journal of sport sciences, 17(4), 338–345

14. WHO. (1978, March). WHO Expert Committee on Arterial Hypertension & World Health Organization. (‎1978)‎. Arterial hypertension: report of a WHO expert committee (‎meeting held in Geneva from 13 to 21 March 1978)‎. World Health Organization. https://apps.who.int/iris/handle/10665/41632


47

2

15. US Department of Labor, Employment and Training Administration. (1991). Dictionary of Occupational Titles, 4th edition. Washington (DC): U.S. Government Printing Office

16. Burns, S. P., & Spanier, D. E. (2005). Break-Technique Handheld Dynamometry: Relation Between Angular Velocity and Strength Measurements. Archives of Physical Medicine and Rehabilitation, 86(7), 1420–1426. https://doi.org/10.1016/j.apmr.2004.12.041


18. Hayes, A. F., & Krippendorff, K. (2007). Answering the Call for a Standard Reliability Measure for Coding Data. Communication Methods and Measures, 1(1), 77–89. https://doi.org/10.1080/19312450709336664

19. McGraw, K. O., & Wong, S. P. (1996). Forming inferences about some intraclass correlation coefficients. Psychological Methods, 1(1), 30–46. https://doi.org/10.1037/1082-989x.1.1.30

20. Shrout, P. E., & Fleiss, J. L. (1979). Intraclass correlations: Uses in assessing rater reliability. Psychological Bulletin, 86(2), 420–428. https://doi.org/10.1037/0033-2909.86.2.420

21. Fleiss, J. L. (1999). Chapter 1: Reliability of measurements. Design and Analysis of Clinical Experiments, New York, Wiley

22. Hamilton, A. L., Killian, K. J., Summers, E., & Jones, N. L. (1996). Symptom Intensity and Subjective Limitation to Exercise in Patients With Cardiorespiratory Disorders. Chest, 110(5), 1255–1263. https://doi.org/10.1378/chest.110.5.1255

Chapter 3

Reference values for isometric muscle strength in children 8 to 17

years of age for the Netherlands

Douma, K. W., Krijnen, W. P., Slager, G. E. C., & van der Schans, C. P. submitted

Chapter 3

50

Abstract Background Several previous studies provided reference values for isometric

muscle strength for children. It is not clear if these reference values are currently

usable. The objective of this study was to determine reference values of isometric

muscle strength for children from 8 to 17 years of age and to compare these

with previously Dutch reported values and recently reported Chilean values.

A secondary objective was to predict muscle strength based on weight, height,

gender, and age.

Methods A sample of 1,252 subjects of which 594 were girls and 658 were boys,

mean (SD) age 13.0 (2.4) years, height 164.0 (13.7) cm and weight 53.9 (14.4)

kg participated in this study. Muscle strength of flexion and extension of knee

and elbow were measured bilaterally using a hand-held dynamometer. Muscle

strength was expressed in Newton and stratified by age. Regression equations

and explained variances were calculated from weight, height, gender, and age.

The mean values and 95% CI were compared to the results from previous studies.

Results The boys were generally stronger than the girls. In the regression

equations, length had a strong effect on elbow flexion strength whereas weight

had a strong effect on knee flexion and extension strength. The explained

variance (R2 adjusted) varied between 0.46 for left elbow extension to 0.66 for

right knee extension and left elbow flexion. Muscle strength in the current Dutch

study was lower in 29 of the 72 values compared to the prior Dutch study (2001)

The difference ranged from 1 Newton in elbow extension for girls 9 years of age

to 187 Newton for knee flexion for boys 16 years of age. Compared to a Chilean

study (2016), Dutch children were systematically stronger in all age and muscle

groups ranging from 15 Newtons in boys 11 years of age to 217 Newtons for knee

extension in boys 15 years of age.

Conclusion Reference values for strength are region and time specific and those

within specific geographical areas should be updated regularly. For modeling

reference values, weight, height, gender, and age should be included in the

regression equations.

Reference values for isometric muscle strength in children 8 to 17 years of age for the Netherlands

51

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BackgroundThe most obvious benefit of strong, healthy muscles in children is the ability

to perform everyday activities such as playing and running. Muscle strength

provides self-sufficiency which contributes to a healthy lifestyle (1,2). Impaired

muscle strength is often ascertained in children with chronic diseases such as

cystic fibroses or after an injury and is one of the major factors contributing to

functional limitations (3,4,5,6). Strength training is therefore often used in training or

rehabilitation programs (5,7). To determine to what extent a child’s muscle strength

is impaired a comparison with accurate reference values is needed (8 9,10,12,13,15).

Reference values are obtained from large scale measurements among groups

stratified by age, height, and gender (8,9,10,11,12,13,14,) which are important to take into

account when predicting muscle strength (9,10,14,15,16). Reference values for muscle

strength in children have been provided in several countries (8,9,10,13,14,15).

It is not clear if reference values for muscle strength can be generalized to other

countries as historic, cultural, and anthropometric characteristics may differ

between countries (16,18). For example, the mean height of the Dutch male is 1.83

meters and 1.71 meters in Chile (17). Additionally, bodyweight has increased in

several countries over the last decades due to eating habits and inactive lifestyles (19,20,21,22,23,14,15). For example, in the Netherlands in 1980, 6% of boys and 11% of

the girls aged 8 to 17 years of age were overweight or obese whereas these

percentages had almost doubled in 2009 (25). In Dutch clinical settings, muscle

strength is evaluated based on reference values obtained in 2001(12). It is not

evident if muscle strength can still be predicted correctly when using previously

found regression equations. The objective of this study is to determine current

muscle strength reference values for children between 8 to 17 years of age and

to compare these with previously reported Dutch and Chilean reference values. A

secondary objective is to analyze to which degree muscle strength can predicted

statistically from weight, height, gender, and age.

MethodsDesignCross sectional study

Chapter 3

52

ParticipantsA convenience sample of subjects from various primary and high schools in

urban and rural areas in the north of the Netherlands participated in the study.

After permission from the executive board of the participating schools, children,

parents, and teachers were informed in writing and asked for permission to

participate in the study. The inclusion criteria were between 8 to 17 years of age

, good general health, and being mentally and physically capable of undergoing

the measurement. A good general health status was defined as a negative score

on the Physical Activity Readiness Questionnaire (PARQ) (26) and participation in

sport classes. For children younger than 12 years of age, parents were asked to

provide informed consent and, for those between 12 to 17 years of age, both the

children and the parents were asked to sign informed consent to participate in

the measurements and approve the anonymized use of the data for scientific

purposes. Muscle strength measurements were performed as an element during

sports and exercise classes and were supervised by the first author (KD).

The Medical Ethical Committee of the University Medical Center Groningen

exempted approval of the study protocol (M15.169717).

Measurement procedureThe participant’s weight, height, age, and gender were recorded. Weight was

measured with an analog Sega 750 weight scale and height with a stature meter

that was fixed on a wooden lath (Seca, gmbh & co Hammer Steindamm 3-25 22089

Hamburg, Germany). Maximal isometric muscle strength was measured with a

MicroFet 2 hand-held dynamometer (Hogan Health Industries, Inc. 8020 South

1300 West, West Jordan, USA). Four major muscle groups were tested in a fixed

sequence on the left and right side; elbow flexion, elbow extension, knee extension,

and knee flexion. Muscle strength was expressed in Newton and stratified by age

and gender. Participants were allowed to choose the side with which to begin.

After completing the measurements, the same sequence was repeated. The mean

of both measurements was used for further analysis for a more precise outcome.

Participants were instructed to maintain their body position throughout the entire

test (Table 1 and Figure 1). The break technique was applied to facilitate the

comparison of results with those of previous studies in the Netherlands and Chile (8,12). In the break method, the examiner overpowered the maximum generated


53

3

force of the participant in order to reliably measure maximal isometric muscle

strength (27,28,29). Participants were instructed to gradually increase the force

to maximum effort in three seconds and to sustain this for two seconds. If the

observer could not break through the generated strength, this was noted on the

administration form and the data was omitted from the study. The participants

were measured by third year physiotherapy students from the Hanze University

of Applied Sciences Groningen, the Netherlands. All students had experience

with hand-held dynamometry but were additionally trained by an experienced

instructor (KD) prior to the actual testing. During measurements, standardized

encouragements were given. All measurements for this research were performed

within a two year period.

Table 1, Description of body positions during measurements

Muscle Action

Joint Position

Localization HHD*

Position Subject

Fixation Subject

Position/Fixation Examiner

Elbow flexion

Neutral shoulder, elbow flexed 90º; upper arm against trunk

Just proximal to styloid process of radius

Lying supine

By body weight; feet against wall

Alongside the table and test subject; leaning backward

Elbow extension

Same as in flexion

Just proximal to ulnar head

Same as in flexion

Same as in flexion

Same as in flexion

Knee flexion Hip and knee flexed 90º

Just proximal to calcaneus

Sitting on table

By body weight and active fixation while gripping table

In front of test subject; feet fixed onto table

Knee extension

Same as in flexion

Just proximal to the talis

Same as in flexion

By body weight and active fixation

In front of test subject; feet fixed onto table

*HHD, Hand-held dynamometer.

Chapter 3

54

Figure 1 illustrates the position of the hand-held dynamometer for the different

measurements.

Figure 1, Position of the hand-held dynamometer for elbow flexion and extension and knee extension and flexion.

Statistical analysesData were analyzed with the Statistical Package for the Social Sciences (SPSS)

version 23.0 and R version 3.2.0. Measurements were determined stratified for

age and gender group means and standard deviations of muscle strength. To

determine the reliability of the two series of measurements per participant, the

intra class correlations (ICC) (two-way random effects model, absolute agreement)

were calculated (30). Interpretation of the ICCs was as follows: ICC < 0.25 low;

0.25 < ICC < 50 moderate; 50 < ICC < 75 good; and ICC > 0.75 excellent reliability (31,32,33). Standard deviation of the mean differences (SDdifference) were determined

to calculate the limits of agreement (LOA), (30) (±1.96 * SDdifference). Linear regression

analyses were performed to statistically predict strength based on, weight, height

gender, and age. A difference in means and corresponding 95% confidence

intervals between current reference values and previously reported reference

values were calculated using a Confidence Interval Analysis (34).

Results

ParticipantsIn total, 1,252 healthy children (594 girls and 658 boys, mean (SD) age 13.2 (2.4),

mean (SD) height 164.0 (13.7) cm, mean (SD) weight 53.9 (14.4) kg, and mean


55

3

(SD) BMI 19.6 (3.4)) participated. The data of two females and three males was

excluded from the analyses because the observer was unable to break through

the participant’s generated strength.

ReliabilityThe ICC coefficients ranged from 0.80 and 0.95. The LOA varied between 44 N for

right elbow extension to 101 N for right knee extension which corresponded with

21% and 36% of the mean measured values, respectively.

Reference valuesThe strength of elbow flexion varied from mean (SD) 115 (35) N for boys 8 years

of age to 280 (102) N for boys 17 years of age and from 115 (28) N for girls 9

years of age to 212 (40) N for girls 17 years of age (Table 2). The strength of elbow

extension varied from mean (SD) 91(18) N for boys 11 years of age to 166 (61) N

for boys 17 years of age and from 78(14) N for girls 10 years of age to 127 (31) N

for girls 17 years of age. Strength of knee flexion varied from mean (SD) 129 N

for boys 8 years of age to 257 (109) N for boys 17 years of age and from 113 (21)

N for girls 10 years of age to 222 (54) N for girls 17 years of age. The strength of

knee extension varied between mean (SD) 150 (40) N for boys 8 years of age to

393 (178) N for boys 17 years of age and from 113 (21) N for girls 10 years of age

to 222 (54) N for girls 17 years of age. Overall muscle strength increased with age

and the difference between boys and girls regarding muscle strength increased

from 14 years of age.

Chapter 3

56

Table 2, Mean (SD) muscle strength in Newton stratified by Side, Age and Gender

Muscle action N BoysLeft Mean (SD)

RightMean (SD)

N GirlsLeftMean (SD)

RightMean (SD)

Age 8 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

18

115(35)

98(29)

129(28)

150(40)

117(32

98(20)

132(30)

156(37)

18

122(38)

98(35)

138(68)

171(69)

120(37)

101(32)

130(48)

164(70)

Age 9 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

40

125(26)

98(18)

140(32)

164(36)

133(31)

95(19)

140(32)

165(37)

32

115(28)

93(19)

115(28)

153(30)

120(24)

92(19)

120(24)

157.(39)

Age 10 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

52

128(20)

88(18)

130(29)

156(44)

131(28)

92(18)

133(28)

164(36)

40

117(25)

78(14)

113(21)

148(36)

121(25)

86(15)

114(25)

144(44)

Age 11 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

32

139(24)

91(18)

136(47)

164(57)

149(26)

96(23)

137(49)

169(59)

34

145(23)

91(20)

121(24)

156(42)

144(41)

95(18)

119(31)

159(52)

Age 12 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

90

163(43)

102(31)

160(44)

226(63)

172(47)

107(31)

167(46)

243(71)

65

161(45)

97(31)

154(54)

221(80)

163(47)

106(32)

154(48)

225(77)

Age 13 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

99

196(38)

118(22)

184(46)

265(66)

206(38)

123(26)

199(54)

280(75)

96

182(84)

108(24)

181(41)

257(74)

188(36)

112(26)

184(41)

262(79)


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3

Muscle action N BoysLeft Mean (SD)

RightMean (SD)


RightMean (SD)

Age 14 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

105

209(54)

132(40)

193(53)

287(83)

218(60)

133(39)

206(57)

301(89)

104

183(47)

108(34)

191(57)

279(92)

189(49)

113(37)

195(56)

285(96)

SD = standard deviation.

Table 2, (continued) Mean (SD) muscle strength in Newton stratified by Side, Age and Gender

Muscle action

N BoysLeftMean (SD)

BoysRightMean (SD)


GirlsRightMean (SD)

Age 15 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

83

266(56)

175(39)

250(61)

355(95)

282(55)

178(39)

267(60)

373(96)

91

193(28)

116(27)

209(44)

304(77)

202(29)

118(26)

215(45)

318(74)

Age 16 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

92

258(68)

161(52)

247)81)

379(107

267(76)

164(52)

251(86)

391(128)

65

185(60)

114(41)

186(67)

293(105)

193(63)

116(63)

195(70)

292(110)

Age 17 year

Elbow Flexion

Elbow Extension

Knee Flexion

Knee extension

39

263(92)

165(65)

249(103)

393(178)

-

280(102)

166(61)

257(109)

390(172)

-

45

207(36)

112(29)

222(54)

346(87)

-

212(40)

127(31)

220(54)

350(91)

-

SD = standard deviation.

Chapter 3

58

In the regression equations, to predict muscle strength, length had a strong effect

on elbow flexion strength whereas weight had a strong effect on knee flexion and

extension strength. The obtained regression equations are presented in Table 3.

The explained variance (R2 adjusted) ranged from 0.46 for elbow extension left to

0.66 for knee extension right and elbow flexion left.

Table 3, Regression equations to predict muscle strength based on side, gender, age, height and weight

Muscle actionEquations

R2 adj.

EFL -166.3 + (22.4*Gender) + (6.6*Age) + (1.1*Height) + (1.3*Weight) 0.66EFR -177.2 + (28.5*Gender) + (7.3*Age) + (1.2*Height) + (1.4*Weight) 0.65EEL -32.5 + (21.3*Gender) + (3.8*Age) + (0.2*Height) + (1.0*Weight) 0.46EER -28.4 + (20.8*Gender) + (3.5*Age) + (0.2*Height) + (1.0*Weight) 0.47KFL -71.4 + (12.9*Gender) + (5.7*Age) + (0.4*Height) + (2.0*Weight) 0.53KFR -78.5 + (20.9*Gender) + (7.5*Age) + (0.3*Height) + (2.0*Weight) 0.46KEL -159.8 + (18.0*Gender) + (15.9*Age) + (0.4*Height) + (2.7*Weight) 0.66KER -176.8 + (24.3*Gender) + (16.4*Age) + (0.4*Height) + (2.8*Weight) 0.56

EFL = Elbow flexion left, EFR = Elbow flexion right, EEL= Elbow extension left, EER = Elbow extension right, KFL = Knee flexion left, KFR = Knee flexion right, KEL = Knee extension left,

KER = Knee extension right, Gender: 1= boy, 0=girl, Age in years of age, Height in cm, Weight in kg, R2 Adj (Adjusted) = Explained variance.

Muscle strength in the current study was significantly less compared to the

previous Dutch study (12) in 29 out of 72 comparisons (Table 4). The differences

in means ranged from 1 N for elbow extension in girls 9 years of age to 187 N for

knee flexion in boys 16 years of age. The differences that were ascertained occur

more frequently and more pronounced in the lower extremity compared to the

upper extremity, 23 and 6 times, respectively, and are more frequently observed

in boys compared to girls 18 and 11 times, respectively. An analysis of confidence

intervals from the current and the recent Chilean study (8) revealed significant

differences for all muscles at all ages except elbow flexion in boys 8 years of age.

The observed differences between our means and the Chilean study ranged from

2 N for elbow flexion in boys 8 years of age to 225 N in knee extension in boys 15

years of age.


59

3

Table 4a, Mean (SD) muscle strength values and the 95% CI of the difference in means for current study and those that of a previous Dutch study (10) and the Chilean study from (6) for boys

Muscle action

Previous DutchMean (SD)

Current-Previous95%CI ΔLCL UCL

Current Mean (SD)

Current- Chilean95%CI ΔLCL UCL

Chilean Mean (SD)

8 year

EF

EE

KF

KE

124(23

90(18)

185(20)

185(41)

-30 16

-7 23

-74 32

-60 2

117(31)

98(20)

132(29)

156(37)

-19 23

31 51

66 102

115(32)

57(11)

72(13)

9 year

EF

EE

KF

KE

134(24)

89(22)

195(40)

194(30)

-21 19

-6 20

-78 -31

-53 -5

133(31)

96(18)

140(32)

165(37)

45 77

15 35

52 90

72(16)

71(14)

94(19)

10 year

EF

EE

KF

KE

173(19)

120(18)

268(48)

267(47)

-60 -24

-40 - 9

-156 -113

-129 -77

131(27)

96(23)

133(27)

164(36)

57 83

25 47

33 67

61(11)

60(8)

114(11)

11year

EF

EE

KF

KE

153(30)

103(31)

218(64)

239(56)

-23 15

-25 11

-118 -44

-111 -29

149(25)

96(23)

137(48)

169(59)

57 81

3 25

15 69

80(13)

82(14)

127(19)

12 year

EF

EE

KF

KE

160(25)

104(31)

201(34)

225(43)

-20 44

-18 24

-65 -3

-30 66

172(47)

107(30)

167(46)

243(71)

67 113

7 37

74 144

82(15)

85(12)

134(27)

13 year

EF

EE

KF

KE

195(26)

128(42)

273(59)

296(70)

-9 34

-21 11

-106 -42

-61 29

207(37)

123(25)

199(53)

280(74)

89 127

18 44

81 157

99(22)

92(11)

161(41)

Chapter 3

60

Muscle action



Current Mean (SD)


Chilean Mean (SD)

14 year

EF

EE

KF

KE

253(50)

158(42)

307(64)

370(61)

-69 -1

-48 -2

-134 -68

-119 -19

218(59)

133(39)

206(56)

301(89)

83 129

1 33

72 142

112(30)

116(29)

194(32)

15 year

EF

EE

KF

KE

278(55)

175(46)

327(76)

362(76)

-29 39

-21 27

-98 -22

-46 68

283(55)

178(38)

267(59)

373(96)

156 210

51 89

170 264

100(17)

108(22)

148(38)

16 year

EF

EE

KF

KE

276(68)

182(64)

382(80)

396(90)

-56 30

-51 15

-185 -79

-84 -74

267(75)

116(41)

195(70)

292(110

95%CI Δ, 95% CI of the difference in means, EF, Elbow flexion, EE, Elbow extension, KF, Knee flexion, KE, Knee extension, LCL, lower confidence limit, UCL, upper confidence limit. Mean values are expressed in N. Significant differences are printed bold and italic.

Table 4b, Mean (SD) muscle strength values and the 95% CI of the difference in means for current study and those that of a previous Dutch study (10) and the Chilean study from (6) for girls

Muscle action



Current Mean (SD)

Current-Chilean95%CI ΔLCL UCL

Chilean Mean (SD)

8 year

EF

EE

KF

KE

115(16)

82(10)

160(23)

166(30

-19 27

-1 39

-61 1

-47 43

120(36)

101(31)

130(47)

164(69)

51 95

35 73

69 144

47(27)

47(21)

64(27)


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3

Muscle action



Current Mean (SD)


Chilean Mean (SD)

9 year

EF

EE

KF

KE

125(28)

91(24)

180(54)

173(57

-23 15

-14 16

-84 -36

-47 15

121(26)

92(19)

120(23)

157(38)

47 69

23 39

48 80

63(10)

61 (9)

93(17)

10 year

EF

EE

KF

KE

134 21)

84(20)

175(29)

159(57)

-30 4

-1 23

-77 -43

-46 18

121(25)

95(17)

114(25)

145(44)

39 63

18 36

25 67

70(11)

67 (6)

99(16)

11year

EF

EE

KF

KE

172(25)

108(25)

246(52)

265(36)

-57 1

-27 1

-154 -100

-144 -71

144(41)

95(17)

119(31)

157(51)

48 86

18 36

25 75

77(17)

68(15)

107(26)

12 year

EF

EE

KF

KE

168(28)

117(24)

221(54)

250(71)

-34 24

-30 8

-99 -35

-74 24

163(47)

106(30)

154(48)

225(76)

59 103

12 40

79 150

82(7)

80(10)

111(11)

13 year

EF

EE

KF

KE

201(23)

118(26)

301(38)

346(49)

-35 9

-22 10

-142 -92

-132 -37

188(36)

112(25)

184(40)

261(78)

91 123

15 40

91 163

81(7)

84(13)

134(26)

14 year

EF

EE

KF

KE

193(32

129(33)

271(76)

280(69)

-41 33

-46 12

-120 -32

-68 70

189(49)

113(37)

195(56)

285(96)

86 124

16 44

83 155

84(13)

83(12)

166(23)

Chapter 3

62

Muscle action



Current Mean (SD)


Chilean Mean (SD)

15 year

EF

EE

KF

KE

198(48)

141(37)

282(61)

325(79

-16 24

-40 -6

-103 -31

-56 41

202(29)

118(26)

215(45)

317(74)

87 117

21 47

135 205

100(32)

84(19)

147(30)

16 year

EF

EE

KF

KE

215(30)

107(36)

336(57)

373(57)

-60 13

-17 35

-185 -97

-149 -13

164(51)

250(85)

391(128)

193(62)

95%CI Δ, 95% CI of the difference in means, EF, Elbow flexion, EE, Elbow extension, KF, Knee flexion, KE, Knee extension, LCL, lower confidence limit, UCL, upper confidence limit. Mean values are expressed in N. Significant differences are printed bold and italic.

DiscussionSignificant and considerable differences were found in the muscle strength

between our data and those from a previous Dutch (12) and Chilean study (8).

Compared to the previous Dutch study, children were less strong in 29 out 72

comparisons up to 187 N in knee flexion in boys 16 years of age. Compared to the

Chilean study, Dutch children, both boys and girls, were overall stronger.

Differences are probably related to the physical dimensions of the children since

there are substantial variances in mean weight and height between the groups

which are both important determinants for muscle strength (9,10,14,15,16). However,

other factors may also play a role such as cultural, ethnic, or geographical

differences. For example, in the Netherlands, 28% of Dutch children aged 12 to

17 met the recommended level of physical activity for youth in 2014 (20). In Great

Britain, 18% of the children between 5 to 15 years of age met the recommended

level for physical activity in 2013 (19). This difference in physical activity might

partially explain differences in strength but data about physical activity level in

Chilean children are unknown.


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Our findings show that reference values from one country cannot simply be

generalized to another country as they appear to be region specific. Additionally,

differences in inclusion and exclusion criteria may explain differences between

studies. Obese children were excluded in the Chilean study (8) while, in our study,

obesity was not an exclusion criterion in order to achieve a representative sample

of Dutch children.

The muscle strength, especially in the lower extremity, of the current study was

significantly less compared to the previous Dutch study (2001) (12). Prior to the

study, we expected to find greater muscle strength as the children participants

were, on average, heavier (current study mean (SD) weight 48.0 (8.8) kg; previous

Dutch study, 46.4 (6.2) kg). It can be assumed that supporting a heavier bodyweight

results in physiologic adaptations in the lower limb muscles with increased

muscle strength. The commonly seen increase in passive lifestyles (21,22,23,24,25) with

concomitant decreased physical activity might explain muscle strength in the

current population. These findings illustrate that reference values can only be

used for a limited time as they appear to be time-specific.

Hand-held dynamometry is a relatively inexpensive and a reliable instrument for

measuring muscle strength, however, it has some practical disadvantages. It is

sometimes impossible to break through a subject’s generated strength. This is

a commonly described phenomenon that might induce substantial error when

frequently observed. However, in our study, it occurred for only five of the 1252

participants (0.4%) and is probably of minor influence in clinical settings when

testing children with decreased muscle strength.

Study limitationsWe tested a convenience sample of children from schools that may not be

completely representative for all Dutch children. However, by including children

from urban and rural areas as well as from different socioeconomic backgrounds,

we assume that our sample is sufficiently representative. Since the majority of the

children in this study were Caucasian while a relatively small number of immigrant

children was included, the reference values obtained seem less representative for

the latter group.

Chapter 3

64

ConclusionReference values for muscle strength are made available for the present Dutch

population of children between 8 and 17 years of age. Reference values for muscle

strength are time and geographically specific. For adequate comparison, it is

necessary to regularly update reference values within a specific geographical area

due to changes in lifestyle and bodyweight.


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Building Relationship to Health and Solid Movements Approaches In Schools Children’S. International Journal of Physical Education & Sports Sciences, 13(1), 17–23. https://doi.org/10.29070/13/56092

2. Boreham, C., & Riddoch, C. (2001). The physical activity, fitness and health of children. Journal of Sports Sciences, 19(12), 915–929. https://doi.org/10.1080/026404101317108426

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9. Douma, R. K. W., Soer, R., Krijnen, W. P., Reneman, M., & van der Schans, C. P. (2014). Reference values for isometric muscle force among workers for the Netherlands: a comparison of reference values. BMC Sports Science, Medicine and Rehabilitation, 6(1), 10. https://doi.org/10.1186/2052-1847-6-10



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Chapter 4

Reliability of the Q Force; a mobile instrument for measuring isometric

Quadriceps muscle strength

Douma, K. W., Regterschot, G. R., Krijnen W. P., Slager G. E., van der Schans, C. P.,& Zijlstra, W. (2016). Reliability of the Q Force; a mobile instrument for

measuring isometric Quadriceps muscle strength. BMC Sports Science, Medicine and Rehabilitation, 19(8), 4. doi: 10.1186/s13102-016-0029-x

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AbstractBackground The ability to generate muscle strength is a pre-requisite for all human

movement. Decreased Quadriceps muscle strength is frequently observed in older

adults and is associated with a decreased performance and activity limitations.

To quantify the Quadriceps muscle strength and to monitor changes over time,

instruments and procedures with a sufficient adequate reliability are needed. The

Q Force is an innovative mobile instrument for measurement of isometric muscle

strength in various degrees of extension. Measurements between 110 and 130

degrees extension present the highest values and the strongest increase after

training.

The objective of this study is to determine the test-retest reliability of isometric

Quadriceps muscle strength measurements, in 110 degrees knee extension using

the Q Force in older adults.

Methods Forty-one healthy adults (mean (SD) age 81.9 (4.9) years, 13 males and 28,

females were included in the study. Isometric strength of the Quadriceps muscle

was assessed using the Q Force at 110 degrees knee extension. Participants were

measured on two occasions with a three to eight day interval between occasions.

Intraclass correlation coefficients (ICCs) and limits of agreement (LOA) were

calculated and t-tests were performed.

Results All ICCs were higher than 0.75. LOA for the peak torque, for the left side

were -18.6 N to 33.8 N and for the right side -9.2 N to 26.4 N. Small systematic and

significant differences in means were found between measurement occasions.

Conclusion The present study shows that the Q Force has excellent test-retest

reliability, but LOA are substantial. Since the Q Force is relatively cheap and mobile

it is suitable for application in various clinical settings, however, its capability

to detect changes in muscle force over time is limited but similar to existing

instruments.

Reliability of the Q Force; a mobile instrument for measuring isometric Quadriceps muscle strength

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BackgroundMuscle strength is essential for all physical activities such as activities of daily

living, work, sports and maintaining posture (1,2,3,4). Reduced muscle strength is

frequently apparent in older people and creates a potential risk for a decline of

activities (1,2,3,4,5,6,7,8). Reduced muscle strength may induce balance deficits, increase

the risk of falling (3,4,5,6,7,8,9,10), and it predisposes for disability, premature nursing

home admission, and ultimately premature mortality (5,11). Functional walking tests

and rising form a chair, such as the timed up and go test, are used to predict the

occurrence of future falls. Retrospective studies have shown that these tests are

associated with a history of falls but the predictive capacity is limited (8,11,12).

The Quadriceps muscle is important due to its major contribution walking stairs,

rising from a chair, and walking (3,4,7). To quantify Quadriceps muscle strength and

to monitor changes over a period of time, muscle strength measurement with

sufficient reliability is required. Several methods to measure muscle strength are

available. The Medical Research Counsel Scale (MRC) is the most commonly and

clinically used scale. The MRC scale ranges from, 0 to 5. Unfortunately, this scale

is inaccurate and inefficient in detecting changes over a period of time (14,15,16,17,18).

MRC grade 4 covers a wide range from 5 up to 99 % of the generated strength (19).

More precise measurements are possible with hand-held dynamometry allowing

muscle strength to be measured on a continuous scale. Hand-held dynamometry

has been demonstrated to have good test retest reliability with intra class

correlation coefficients of 0.8 or higher (19, 20, 21,22). Measurements with a hand-held

dynamometer, are required to be performed in a joint position of 90 degrees

flexion (23,24,25). Joint positions other than 90 degrees flexion however, produced

greater maximal muscle strength values (26,27,28), as well as a greater sensitivity for

detecting changes over time (27). For the knee the highest values were recorded

using measurements at 110 and 130 degrees extension (28). Besides the joint

position, another limitation of hand-held dynamometry is the effect of the weight

and strength of the observer on outcomes. Stronger testers may obtain routinely

higher values (29,30,31). Fixation of healthy participants during measurement can be

more be difficult (22,23,32). Thus observer capacity may negatively influence reliability

and validity of muscle strength measurements using a hand-held dynamometer (22,23,32). An additional limitation in non-computerized type of muscle strength

measurements is that they do not provide insight in coordination, slope, and

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duration of the contraction. Whereas, sustainable and repetitive contractions are

required in sports, and activities of daily living.

Another type of measurement is isokinetic muscle strength measurement.

Isokinetic equipment is capable of measuring muscle strength in different body

positions and angles, presenting an abundance of graphical, numerical, and

derivative information which are considered to be the gold standard (33,34).

The Q Force chair has been recently developed as a successor of the Quadriso Tester (35) to measure isometric muscle strength of the Quadriceps muscle in different

joint angles. Advantages of the Q Force compared to other instrumentation is that

it is transportable and can be employed easily in a clinical setting. It provides,

similar to isokinetic instrumentation, relevant graphical and calculated numerical

information about the contraction besides measured peak values. Currently test-

retest reliability of the Q Force in older adults is unclear. Therefore the objective of

this study was to determine the test-retest reliability of isometric muscle strength

measurements with the Q Force in older adults.

MethodsThe Medical Ethics Committee of the University Hospital Groningen approved this

study (M11.110634).

ParticipantsInclusion criteria were, at least 70 years of age, being able to walk ≥10 meters

without support, rise from a chair without resources or assistance, absence of

cardiovascular/respiratory or neurological disorders, absence of comorbidity

or cognitive disorders that influence mobility, understanding, or execution of

measurements, no current or recent participation in exercise programs or any

other physical intervention, and no orthopedic surgery or stroke within the last six

months. Participants were included after providing and signing informed consent.

DesignReliability study.


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MeasurementsMuscle strength was assessed on two occasions within three to eight days. Four

trials were performed on each occasion at approximately the same time of the

day. If the participant was unable to perform four trials for any reason, fewer trials

were performed and used for analysis.

DeviceThe Q Force has been constructed for measuring isometric Quadriceps muscle

strength. It consists of a chair with an attached, adjustable fi xed leg brace at the

front. Three sensors are located in the brace to determine the generated force

(Newton), the angle between the horizontal chair surface and the brace and

the distance between the force transducer and the rotation axle of the brace

(millimeter). All three signals pass through an analog-digital converter, are read

and saved on a laptop.

Figure 1, Schematic view, Q Force

A = Back support, B = Seat, C = Fixed brace, D= Base, E= Astrolabe/Goniometer,

F = Force transducer, G= Distance transducer

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Figure 2, Side view of Q Force with fixed brace at the front

The chair incorporates a solid frame, base, back support, and a seat. Bars are

fitted at both sides of the seat for manual fixation. The height of the sitting

surface is fully adjustable. At the left and right bottom of the seat, in an anterior

posterior direction, rails are attached to which the brace is connected so that both

the left and right leg can be tested. The fixed brace consists of a fixed horizontal

and an adjustable distal component with a hinge in between. The brace can be

slide horizontally via rails. The brace is adjustable to fit the subject’s upper leg

dimensions enabling placing the rotation axis of the brace in the same position

as the rotation axis of the knee for that specific angle. (Fig 2) The measuring angle

of the fixed brace is adjustable between 90° flexion and 180° extension (= full

extension). The force transducer is covered with a pad to minimize pressure on the

subject’s lower leg. The position of the pad is adjustable in vertical and horizontal

directions in accordance with the subject’s dimensions.

Computer and Control

Hardware

The hardware consists of an analog-digital converter (ADC), a force, and a distance

and angle transducer. The ADC is a NI-9219 4Ch Universal Analog input module. As

an interface, the NI USB-9162 converter (National Instruments Corporation, Austin,

USA) is utilized for establishing a USB connection between the ADC and the laptop.

The force transducer is a LLB400 Loadcell which is capable of measuring force up

to 1100 Newton with a break load of 1650 Newton (Futek, Irvine). The distance


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transducer is a CLS1321 Linear potentiometer (Active Sensors Indianapolis). The

angle is measured by a single strike potentiometer.

Software

The accompanying software is developed by the ICT Software Development

Laboratory of the Faculty of Medical Sciences from the University of Groningen

and the University Medical Center Groningen in the Netherlands.

Outcome measuresDuring maximal isometric contraction, Peak Torque (PT) was measured and

Filtered Peak Torque (FPT), Median Peak Torque (MPT) and Average Plateau Peak

Torque (APT) were calculated.

PT is the actually measured peak value and is calculated as Fmax * r + fixation

torque, where Fmax is the registered maximal force, r is the distance between the

knee joint rotation point and the sensor on the lower leg and fixation torque is the

torque required keeping the lower leg stabilized against gravity. Arrow 2 in Figure

3 illustrates the PT value.

FTP is the APT of the sample that recorded the PT value (1) with the sample before

(-1) and the sample after (+1) this sample and is calculated as

FPT .

Arrow 1 and 3 in Figure 3 indicate FPT.

MPT is the median of the total torque above the level of 0.5 * PT. This is calculated

as: median total torque = median (total torque (a:b)) where a is the moment where

total torque is greater than 0.5 * PT for the first time, and b is the moment where

total torque is smaller than 0.5 * PT for the first time. Line a-b in Figure 3 represents

50 percent of the PT level. Line c-d represents the MPT. APT is the value above 50

percent of the PT level. It is the APT over the plateau phase. It is calculated as the

average (total torque (c:d)), where c is the initial sample following sample a when

the absolute difference with sample c -1 is less than 4 Nm. Sample d is the sample

following sample a where the absolute difference with sample d -1 is smaller

than 4 Newton meter (Nm). Point e in Figure 3 represents the first sample where

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the increase of the generated force is less than 4 Nm, and point f represents the

last sample where the decline of the generated force f is less than 4 Nm. Line

e-f represents the calculated value. This means that the plateau phase between

samples c and d can be recognized in which the absolute differences between the

consecutive samples during this plateau are less than 4 Nm. This was considered

as a reliable contraction representing the maximum generated torque which could

be used for analysis. The level of elevation of this plateau corresponds with the

generated torque. The mass and center of gravity of the lower leg were calculated

described previously (36). The sample ratio which recorded the generated forces

was 2Hz.

Figure 3 represents a graphic interpretation of the outcome measures.

Figure 3, Graphic representation of the measured and calculated values.

The Y axis represents the generated torque in Nm. while the X axis represents

time. The letters g and h correspond with the start and the end of the contraction,

a-b represents 05 * PT level, c-d represents the MPT and e-f represents the APT.

Data acquisitionAll algorithms for data acquisition were programmed and collected in Matlab

Mathworks 7, Nathick, USA. The collected data were transferred from Microsoft

Excel 2010 files for statistical analysis.


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Measurement procedureThe angle of the fixed leg brace was positioned at 110° extension and the subject

was subsequently positioned in the chair without back support and with the back

of their knee positioned against the seat. The lateral condyle of the femur was

aligned with the rotation point of the Q Force. The force transducer was positioned

3 centimeters above lateral malleolus. The tuberosity of the tibiae was aligned

with the sensor to prevent adduction, abduction, or rotation in the knee or hip

in the starting position. The computer program was initiated as the subject was

instructed to elevate the lower leg to minimize pressure on the force transducer

in order to calibrate the system. The distance between the transducer and the

rotation point was determined to calculate the generated torque and the average

knee angle. Additionally, the average distance from the rotation axle to the force

transducer was measured to determine whether the current angle was actually

110 degrees extension. Following the calibration, the actual measurements

began. The left leg was tested first. Participants were allowed to fixate themselves

to the sidebars using their hands. A 1 minute break was administered between the

successive trials. Following each trial, it was evaluated if the contraction had been

maximal by asking, “Was this a maximal effort?” If the contraction had not been

maximal, it was excluded.

Instruction of the participantThe participants were instructed as follows: “Extend your knee as forceful as

possible. I will measure the strength you will generate. You are allowed to fixate

yourself to the side bars using your hands. Each leg will be tested four times each

with a one minute break in between. I will encourage you and tell you when to

start and when to stop. The maximal contraction has to endure for three seconds.

Build up your contraction gradually and let go slowly.”

Statistical AnalysesAll data were analyzed with the statistical programming language string R version

3.1.2 2014. To determine reliability an intraclass correlation coefficient (ICC)

(two-way, absolute agreement) was calculated. Limits of agreement (LOA) were

calculated as ± 1.96 * SD of the mean difference (37). The LOA were calculated

for each pair of measurements and were interpreted with regard to the clinical

relevance to their size.

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Bland and Altman plots were constructed with the difference and the mean of two

measurements for each subject. Means, standard deviation, mean difference, and

standard deviations were calculated for descriptive purposes. The paired t-test

was used to analyze systematic differences between occasion 1 occasion 2. ICCs

were interpreted as follows: ICC<0.25 low; 0.25<ICC<0.50 moderate; 0.50<ICC<0.75

moderate to good; and ICC>0.75 is excellent reliability (38,39,40). A level of 0.05 was

considered significant.

ResultsParticipantsForty-one healthy adults (mean (SD) age 81.9 (4.9) years, mean (SD) body weight

78.5 (13.0) kg and mean (SD) body height 165.3 (5.8) cm) 13 males and 28 females

were included.

Outcome measuresTable 1, Mean (SD) of the measured and derivative values, intraclass correlation coefficients, the t-test outcomes and the LOA’s for the left and right leg

Value Occasion 1Mean (SD)

Occasion 2Mean (SD)

Diff.Mean (SD)

p Valuet-test

ICC LowerLOA

UpperLOA

LOA%Mean

PT 63.1 (27.2) 70.7 (29.2) 7.6 (13.4) 0.0078 0.89 -18.6 33.8 39.1

PT 66.1 (30.4) 74.8 (34.2) 8.6 (9.1) 0.0001 0.92 -9.2 26.4 25.1

FPT 62.5 (27.0) 70.2 (29.1) 7.7 (13.5) 0.0077 0.88 -18.8 34.2 39.9

FPT 65.6 (30.3) 74.0 (34.1) 8.4 (9.1) 0.0001 0.96 -9.4 26.2 25.5

MPT 58.5 (26.0) 66.4 (28.5) 7.9 (12.5) 0.0037 0.89 -16.6 32.4 39.2

MPT 62.0 (29.1) 69.9 (32.9) 7.9 (9.0) 0.0001 0.96 -9.7 25.5 26.7

APT 58.3 (26.2) 65.9 (28.8) 7.6 (12.9) 0.0058 0.80 17.6 32.8 38.7

APT 61.8 (29.6) 70.2 (33.5) 8.4 (9.1) 0.0001 0.96 -9.4 26.2 26.9

PTL; Peak Torque, FTP; Filtered Peak Torque, MPT; Median Peak Torque, APT; Average Plateau Peak Torque, expressed in Newton, Diff; Difference ICC; Intraclass Correlation Coefficient, LOA; Limit of Agreement, LOA is expressed as percentage of mean of occasion1 and occasion 2.

Torque values were significantly higher of the second occasion compared to the

first occasion (mean difference ranged from 7.6 to 8.6) (Table 1). ICCs were higher

for the right side than for the left but all ICCs were greater than 0.75. The LOA were

smaller for the right leg compared to the left and were relatively large, 17.6 to 26.5


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Newton, representing between 25.2% to 39.9% of the mean values of occasion 1

and occasion 2 (Figures 4 to 12).

Figures 4 through 11 present Bland and Altman plots of the limits of agreement

between occasion 1 and occasion 2 of the mean difference of the PT; the mean

MPT; the mean MPT; and the mean FPT of the left and right leg, respectively.

Figure 4, Limits of Agreement for meanPeak Torque measurements-left

Figure 5, Limits of Agreement for mean Median Peak Torque measurements-left

Figure 6, Limits of Agreement for meanPlateau Torque measurements left

Figure 7, Limits of Agreement for mean Filtered Peak Torque measurements left

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Figure 8, Limits of Agreement for mean Peak Torque measurements-right

Figure 9, Limits of Agreement for mean Median Peak Torque measurements-right

Figure 10, Limits of Agreement for mean Plateau Peak Torque measurements right

Figure 11, Limits of agreement for Filtered Peak Torque measurements right

The uninterrupted horizontal line was located above zero in all cases due to the

systematic difference between occasion 1 and occasion. The variation of all of the

measurements did not increase with increasing Q Force torque, and only minimal

outlying points were observed. The right leg measurements resulted in smaller

LOA than those for the left.


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Discussion Muscle strength measurements in elderly using the Q Force at 110 degrees

extension of the knee are reliable. ICCs exceed 0.75 which indicates excellent test-

retest reliability (38,39,40). However, the obtained LOA’s are substantial indicating

considerable variation in measurement results. The mean values at the second

measurement are significantly higher than those at the first measurement. ICCs

and LOA are consistently better for the right leg compared to the left. The ICCs

indicate that the measurements using the Q Force can be used on a group level (38,39,40). The encountered ICC coefficients are between 0.80 and 0.95 and are

consistent with ICCs found for other reliability studies regarding muscle strength

measurement (20,21,22,23,32,41,42,43,44). The ICCs for the outcome measures, PT, FPT, MPT

and APT were similar, indicating that reliability can be generalized over different

types of muscle strength measures. We measured muscle strength at 110

degrees knee extension. Studies based on different degrees of extension found

ICC coefficients between 0.87 and 0.99 and are in accordance with our findings (20,21,22,23,32,41,42,43,44). ICC coefficients provide information regarding reliability of the

instrument. The ICCs do not provide information on the magnitude of the intra

individual variation between observations (37). These intra individual variations

are expressed in LOA . In general variation in measurement results can be

influenced by several sources of variation such as the time of the day, type of

measurement, subject, observer, and protocol. The LOA we found are substantial

and vary between 15.7 and 23.6 Nm which corresponds to 22.5% and 36.0% of the

overall mean of the measurements in occasion 1 and 2. These outcomes indicate

that a true change, improvement or deterioration, can only be detected if it is at

least 22.5% in magnitude. Other studies with different type of instrumentation

and different populations found similar results (20,45). LOA for the right side were

smaller than on the left. This difference may be explained by right-side dominance

of the majority of a population is (46), indicating an increased neural drive to the

dominant right leg resulting in more consistent values.

Systematic differences were found between the first and second occasion.

Means in the second occasion were approximately 10% higher than in the first

occasion. Other studies using isokinetic devices or in pre trials prior to the actual

measurement also found systematic differences or a tendency to higher values

for the second measurement occasion(44,47,48,49,50,51). Several studies suggest that

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fear, a learning effect or increased muscle recruitment may be responsible for

these larger values (20,28,44,48,49,50,51).

Strength and weaknessesIn our study we tested a population of healthy older adults. It does not provide

information about reliability of measurements in for example chronically ill people

or healthy working adults. We did not register if people were left or right side

dominant, limiting the insight in the origin of the observed difference in ICC, LOA

between left and right side. We did not perform pre trials on occasion 1 which

might have contributed to the observed differences between the occasions.

Though strength measurements reflect the Quadriceps muscle force no valid

procedures are available translating muscle strength into function. Therefore

interpretation of strength measurement should be performed with caution.

ConclusionForce measurements in 110 degrees extension have excellent reliability, but

substantial LOA. The LOA indicate a limited capability to detect changes in muscle

strength over time. Since the Q Force is relatively cheap and mobile it seems

suitable for application in various clinical settings. Future studies should investigate

the degree in which its discriminative ability can be improved especially in older

adults.


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12. Beauchet, O., Fantino, B., Allali, G., Muir, S. W., Montero-Odasso, M., & Annweiler, C. (2011). Timed up and go test and risk of falls in older adults: A systematic review. The journal of nutrition, health & aging, 15(10), 933–938. https://doi.org/10.1007/s12603-011-0062-0

13. de Souza Moreira, B., Mourão Barroso, C., Cavalcanti Furtado, S. R., Sampaio, R. F., Drumond das Chagas e Vallone, M. L., & Kirkwood, R. N. (2014). Clinical Functional Tests Help Identify Elderly Women Highly Concerned About Falls. Experimental Aging Research, 41(1), 89–103. https://doi.org/10.1080/0361073x.2015.978214

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20. Wang, C. Y., Olson, S. L., & Protas, E. J. (2002). Test-retest strength reliability: Hand-held dynamometry in community-dwelling elderly fallers. Archives of Physical Medicine and Rehabilitation, 83(6), 811–815. https://doi.org/10.1053/apmr.2002.32743

21. Roy, M. A. G., & Doherty, T. J. (2004). Reliability of Hand-Held Dynamometry in Assessment of Knee Extensor Strength After Hip Fracture. American Journal of Physical Medicine and Rehabilitation, 83(11), 813–818. https://doi.org/10.1097/01.phm.0000143405.17932.78

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Chapter 5

Are repeated strength measurements required

for older adults?

K.W., Douma, Slager, G. E. C., W.P., Krijnen, & van der Schans, C. P.submitted

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AbstractBackground The strength of the Quadriceps muscle is important because it is

needed in many activities of daily living. Decreased Quadriceps muscle strength is

related to aging and may lead to an inability to perform activities of daily living. To

quantify decrease in Quadriceps muscle strength, it is important that Quadriceps

muscle strength can reliably and validly be measured. A commonly used

instrument to do so is the hand-held dynamometer. It possesses good reliability

and is relatively simple to use. In clinical practice, often three repetitions are used

to reliably measure Quadriceps muscle strength. Currently, it is unclear whether it

is necessary to conduct repeated measurements in older adults in order to obtain

reliable estimates of Quadriceps muscle strength outcomes. The objective of this

study was therefore to analyze outcomes of repeated Quadriceps muscle strength

measurements using a hand-held dynamometer in older adults.

Methods A sample of 44 individuals comprising 14 male and 30 female older adults

participated in the study. The mean (SD) age was 76.8 (7.4) years , bodyweight 79.5

(12.8) kg, and body height 167.3 (6.1) cm. Measurements were performed using

a MicroFet 2 hand-held dynamometer on four separate days (2-day intervals)

using three consecutive repetitions of the left and right Quadriceps muscle with

a 1-minute break in between at each repetition. A linear mixed-effects model

regression analysis was performed.

Results No significant effect for trials within days or between days was found. The

standard errors were similar between left and right side, ranging from 3 to 13 N.

Conclusion A single measurement is sufficient for assessing muscle strength in

groups of older adults.

Are repeated strength measurements required for older adults?

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BackgroundMuscle strength is essential for all activities of daily living and is of special interest

in the chronically ill and the growing population of older adults with declining

muscle strength (1,2,3,4,5,6). The Quadriceps muscle is of special interest because it

is needed in many activities of daily living (6) . Decreased skeletal muscle strength

is related to aging and, at older ages, may lead to, for instance, an inability to

perform tasks of daily living and loss of individual independency (7,8,9). Quadriceps

muscle strength declines by 1.3 to 5.0 % per year after 70 years of age (10,11,12).

Decreased Quadriceps muscle strength in older adults leads to an increased risk

for falls (2,3,4,7) and, in combination with an increased susceptibility for fractures,

falls may lead to nursing home admittance or even premature death (8,12,13,14,15,16,17).

Muscle strength measurements enable quantifying the decline of muscle strength

with age or to evaluate the effectiveness of an exercise program for which several

instruments are available. A commonly used instrument to determine isometric

muscle strength is the hand-held dynamometer. It has good intra- and inter

observer reliability in various settings, is simple to use, small, and reasonably

inexpensive (18,19,20,21).

Muscle strength in clinical situations is frequently assessed on a single day with

measurements repeated three times (18,20,21,22,23,24,25. Studies that measured muscle

strength repeatedly within several measurement days show inconclusive results.

Some studies indicate similar outcomes (18,22,23,24,25), other studies found higher

outcomes (32,33,34,35,36,37), and one study ascertained lower outcomes on the second

measurement day (36). An increase in strength on the second measurement day

cannot be explained by a physiological training effect as the time span between

two measurement days was too brief. A learning effect may be present. Increased

test experience with muscle strength measurement may result in higher outcomes

of consecutive measurements within a single day or a second measurement day (1).

Currently, it is unclear whether it is necessary to conduct repeated measurements

in order to obtain a reliable muscle strength estimate.

The objective of this study was therefore to analyze outcomes in older adults

of repeated Quadriceps muscle strength measurements using a hand-held

dynamometer.

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MethodsStudy population A convenience single institution sample of older adults who live in a retirement

home in the city of Groningen, the Netherlands, participated in this study. Prior

to the study, the director of the retirement home was informed about the

objective and content of the study and asked for permission to perform it. After

permission, a selection of participants was made in consultation with supervisors

of the movement programs. Older adults who suffered from dementia or

cognitive disorders or severe osteoporosis that prevented them from adequate

muscle strength testing were not asked to participate in the study. The remaining

inhabitants of the retirement home were informed with a letter about the study.

One week later, they were personally asked to participate in the study by the

students of physiotherapy who performed the measurements. The Medical Ethical

Committee of the University Medical Center Groningen exempted approval of the

study protocol (M16.192575).

Inclusion and exclusion criteriaInclusion criteria were being able to walk 20 meters with or without resources and

rise from a chair without resources or assistance. Exclusion criteria were systolic

and diastolic blood pressures exceeding 159 and 100, respectively, surgery

procedures, cerebrovascular accidents in the past six months, blood coagulation

disorders, chronic prednisone use, cognitive disorders that affect mobility,

understanding or execution of the measurements, and a positive score on the

Physical Activity Readiness Questionnaire (PARQ).

Design

Repeated measurement study

Measurements were performed on four separate measurement days with

two days in between using three consecutive repetitions of the left and right

Quadriceps muscle with a 1-minute break in between repetition. The participants

were allowed to begin the test with the leg that they preferred. After finishing

three repetitions, the opposite leg was measured. The measurement instrument

was a MicroFet 2 hand-held dynamometer (Hoggan Health Industries, Inc. 8020

South 1300 West, West Jordan, UT, USA). Participants were seated on a chair


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without back support with hips and knees flexed 90 degrees. This position had

to be maintained during the measurement. The dynamometer was positioned

anteriorly on the most distal part of the tibia. (Figure 1) Participants were asked

to gradually increase their muscle strength to a maximum in three seconds. The

‘break technique’ was applied.

Instruction of the participants Participants were instructed as follows: “Sit straight on the chair with your knees

and hips flexed 90 degrees, maintain this position and extend your knee as

forceful as possible, and build up your contraction gradually in three seconds. I will

measure the strength you will generate. You can fixate yourself, using your hands.

I will encourage you and tell you when to stop.” Observers provided standardized

encouragement. Following each trial, it was evaluated if the contraction had been

maximal by asking, “Was this your maximal strength?”

Figure 1, Hand-held dynamometer positioned anteriorly on the most distal part of the tibia

Statistical analyses Data were analyzed with SPSS 23 and R 3.2.0.(38). The means, standard deviation,

and mean difference were calculated. A linear mixed-effects model regression

analysis with fixed and random person effects was used to analyze differences

between trials and measurement days.

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In the linear mixed-effects model, the measurement results from a participant are

decomposed as the sum of fixed and random effects. Time effects are treated as

fixed whereas intercept effects of participants are treated as random. The 95%

confidence intervals were calculated.

ResultsParticipantsA sample of 44 individuals comprised of 14 male and 30 female older adults

participated in the study. The mean (SD) age was 76.8 (7.4) years, bodyweight 79.5

(12.8) kg, and body height 167.3 (6.1) cm.

Outcome measures Measurement results are summarized in Table 1.

Table 1, Summary of results of measurements of Quadriceps muscle strength in older adults

Left RightDay Repetition n Mean SD DA Day Repetition n Mean SD DA1 1 44 176 84 187 1 1 44 196 88 198

2 44 191 90 2 44 197 813 44 196 89 3 44 200 86

Day Day2 1 44 195 80 190 2 1 44 206 85 200

2 41 180 72 2 41 191 733 41 196 74 3 41 293 74

Day Day3 1 41 193 82 193 3 1 41 205 78 206

2 41 197 75 2 41 206 833 41 189 72 3 41 207 80

Day Day4 1 41 197 85 196 4 1 41 203 84 207

2 41 197 77 2 41 209 973 41 196 80 3 41 210 93

Muscle strength of the right and left side stratified by repetition (1 to 3) for each measurement day (1 to 4), DA= day average, n = sample size, SD = standard deviation. Values are expressed in Newton.


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Outcomes differed between participants, however, within participants, muscle

strength was fairly stable between repetitions and days (Figures 3 and 4).

Figure 3, Individual data of each participant for the left leg. Colors and dots represent days and repetitions. On the Y-axis, the strength (Newton) for each participant is shown. The dots from left to right represent repetition 1 to 3. Blue represents day 1, purple is day 2, green is day 3, and red is day 4.

Figure 4, Individual data of each participant for the right leg. Colors and dots represent days and repetitions. On the Y-axis, the strength (Newton) for each participant is shown. The dots from left to right represent repetition 1 to 3. Blue represents day 1, purple is day 2, green is day 3, and red is day 4.

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No significant effect for repetitions within days was found (Table 2). A significant

increase (10.3 N) in Quadriceps muscle strength (right side) was determined

between day 1 and day 3 (p=0.036). No other significant effects of days were

ascertained. The standard errors were similar between the left and right sides,

ranging from 3 to 13 N.

Table 2, Results of linear mixed model analyses with fixed effects of days and between trials for the left and right leg.

Left leg Right legValues SE DF t-

valuep- value

Values SE DF t- value

p- value

Intercept 186.2 12.5 294 14.8 <0.001 Intercept 198.9 13.2 294 14.9 <.0001D2-D1 6.1 5.4 108 1.1 0.264 D2-D1 3.4 4.8 108 0.7 0.457D3-D1 9.0 5.4 108 1.6 0.098 D3-D1 10.3 4.8 108 2.1 0.036D4-D1 9.5 5.4 108 1.7 0.082 D4-D1 9.1 4.8 108 1.9 0.059R2-R1 0.2 3.2 294 -0.0 0.950 R2-R1 -1.0 2.8 294 -0.3 0.722R3-R1 3.1 3.2 294 0.9 0.332 R3-R1 1.4 2.8 294 0.5 0.614

SE; standard error, DF; degrees of freedom, *= statistically significant D; Day, R; repetition. The intercept is the reference for determining the effects for repetition, within days and the effect between days. *Reference category is day 1, repetition 1.

Discussion We found no meaningful changes in muscle strength between measurement

days and repetitions within measurement days. Overall, no increase in strength

after repeated testing was determined, with a single exception for the first

measurement for the right side on the third day. Our finding of no effect after

multiple measurements is in accordance with previous studies using hand-held

dynamometry (18,27,28,29,30,31,39,40,42). However, several studies employing machine held

devices found an increase on the second measurement day (33,35,37,41) whereas one

study ascertained a decrease on the second measurement day (37 ). The increase

found using machine-held devices suggests that these types of devices have a

slightly larger sensitivity compared to hand-held dynamometry and require more

practice from participants for them to be able to demonstrate their maximal muscle

strength. Closely related to this issue are the findings about the minimal detectable

change (MDC). For hand-held dynamometry, the MDC range between 17% and 57%

of the measured value (1,30,40,43) and, for machine-held equipment, the MDC ranges

between 14% and 24% of the measured value (36,45). These differences in MDC for

hand-held dynamometry are probably related to weight, strength, gender, and


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experience of the observer (26,29,43,45,46,47). However, also patient related factors such

as discomfort at the site of the sensor or variations in location of the sensor may

play a role (26,29,43,45,46,47). In the case of machine-held devices, the observer related

variation and location errors are probably smaller which leads to a less obtrusive

fixation and apparently a more sensitive and precise measurement. Although

we found no significant day effects, results of the measurements on day 2 to 4

were somewhat larger than on day 1. Further, we observed minimal differences

between days or repetitions in some individuals suggesting that a learning effect

might be present. For these participants, multiple measurements are beneficial

for obtaining a more valid outcome of muscle strength measurements.

Conclusion A single measurement is sufficient to quantify muscle strength at group level.

However, for individual measurements in a therapeutic setting where certainty

about changes is required, we advise the therapist to execute three repetitions on

a single measurement day.

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19. Bohannon, R., W. (2012). Minimal detectable change of knee extension force measurements obtained by handheld dynamometry from older patients in 2 settings. Journal of Geriatric Physical Therapy, 35(2), 79-81. doi:10.1519/JPT.0b013e3182239f64

20. Beenhakker, E. A. C., van der Hoeven, J. H., Fock, J. M., & Maurits, N. M. (2001). Reference values of maximum isometric muscle force obtained in 270 children aged 4–16 years by hand-held dynamometry. Neuromuscular Disorders, 11(5), 441–446. https://doi.org/10.1016/s0960-8966(01)00193-6.


22. Andersen, L. B., & Henckel, P. (1987). Maximal voluntary isometric strength in Danish adolescents 16-19 years of age. European Journal of Applied Physiology and Occupational Physiology, 56(1), 83–89. https://doi.org/10.1007/bf00696381

23. Shah, S., Nahar, P., Vaidya, S., & Salvi, S. (2013). Upper limb muscle strength & endurance in chronic obstructive pulmonary disease. The Indian journal of medical research, 138(4), 492–496


25. Eek, M. N., Kroksmark, A.K., & Beckung, E. (2006). Isometric Muscle Torque in Children 5 to 15 Years of Age: Normative Data. Archives of Physical Medicine and Rehabilitation, 87(8), 1091–1099. https://doi.org/10.1016/j.apmr.2006.05.012

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26. Kelln, B, M., McKeon, P. O., Gontkof, L. M., & Hertel, J. (2008). Hand-held dynamometry: Reliability of lower extremity muscle testing in healthy, physically active, young adults. Journal of Sport. Rehabilitation, 17(2):160-170. doi:10.1123/jsr.17.2.160

27. Barden, H. L. H., Nott, M. T., Baguley, I. J., Heard, R., & Chapparo, C. (2012). Test-retest reliability of computerised hand dynamometry in adults with acquired brain injury. Australian Occupational Therapy Journal, 59(4), 319–327. https://doi.org/10.1111/j.1440-1630.2012.01016.x

28. Trudelle-Jackson, E., Jackson, A. W., Frankowski, C. M., Long, K. M., & Meske, N. B. (1994). Interdevice Reliability and Validity Assessment of the Nicholas Hand-Held Dynamometer. Journal of Orthopaedic & Sports Physical Therapy, 20(6), 302–306. https://doi.org/10.2519/jospt.1994.20.6.302


30. Pfister,P. D., De Bruin, E. D., Sterkele, I., Maurer, B., De Bie, R. A., & Knols, R. H. (2018). Manual muscle testing and hand-held dynamometry in people with inflammatory myopathy: An intra- and interrater reliability and validity study. Archives of Physical Medicine and Rehabilitation, 1–22. https://doi.org/10.1371/journal.pone.0194531

31. Crompton, J., Galea, M. P., & Phillips, B. (2007). Hand-held dynamometry for muscle strength measurement in children with cerebral palsy. Developmental Medicine & Child Neurology, 49(2), 106-111. doi:10.1111/j.1469-8749.2007.00106.x

32. Douma, K. W., Regterschot, G. R. H., Krijnen, W. P., Slager, G. E. C., van der Schans, C. P., & Zijlstra, W. (2016). Reliability of the Q Force; a mobile instrument for measuring isometric quadriceps muscle strength. BMC Sports Science, Medicine and Rehabilitation, 19(8), 4. https://doi.org/10.1186/s13102-016-0029-x

33. Ritti-Dias, R. M., Basyches, M., Câmara, L., Puech-Leao, P., Battistella, L., & Wolosker, N. (2010). Test-retest reliability of isokinetic strength and endurance tests in patients with intermittent claudication. Vascular Medicine, 15(4), 275–278. https://doi.org/10.1177/1358863x10371415

34. Kienbacher, T., Kollmitzer, J., Anders, P., Habenicht, R., Starek, C., Wolf, . . . Ebenbichler, G. (2016). Age-related test-retest reliability of isometric trunk torque measurements in patiens with chronic low back pain. Journal of Rehabilitation Medicine, 48(10), 893–902. https://doi.org/10.2340/16501977-2164

35. Sole, G., Hamrén, J., Milosavljevic, S., Nicholson, H., & Sullivan, S. J. (2017). Test-Retest Reliability of Isokinetic Knee Extension and Flexion. Archives of Physical Medicine and Rehabilitation, 88(5), 626-631. doi:10.1016/j.apmr.2007.02.006


37. Almosnino, S., Stevenson, J. M., Bardana, D. D., Diaconescu, E. D., & Dvir, Z. (2012). Reproducibility of isokinetic knee eccentric and concentric strength indices in asymptomatic young adults. Physical Therapy in Sport, 13(3), 156–162. https://doi.org/10.1016/j.ptsp.2011.09.002


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38. R Core Team. (2018). A Language and Environment for Statistical Computing. R Core Team, R Foundation for Statistical Computing, Vienna, Austria

39. Moxley-Scarborough, D., Krebs, D. E., & Harris, B. A. (1999). Quadriceps muscle strength and dynamic stability in elderly persons. Gait and Posture, 10(1), 10-20. doi:10.1016/S0966-6362(99)00018-1


41. Maffiuletti, N. A., Bizzini, M., Desbrosses, K., Babault, N., & Munzinger, U. (2007). Reliability of knee extension and flexion measurements using the Con-Trex isokinetic dynamometer. Clinical Physiology and Functional Imaging, 27(6), 346–353. https://doi.org/10.1111/j.1475-097x.2007.00758.x

42. Wang, C. Y., Olson, S. L., & Protas, E. J. (2002). Test-retest strength reliability: hand-held dynamometry in community dwelling elderly fallers. Archives of Physical Medicine and Rehabilitation, 83(6), 811-815. doi: 10.1053/apmr.2002.32743

43. Bohannon, R. W. (2012). Minimal detectable change of knee extension force measurements obtained by handheld dynamometry from older patients in 2 settings. Journal of Geriatric Physical Therapy, 35(2), 79-81. doi:10.1519/JPT.0b013e3182239f64.

44. Kean, C. O., Birmingham, T. B., Garland, S. J., Bryant, D. M., & Giffin, J. R. (2010). Minimal detectable change in quadriceps strength and voluntary muscle activation in patients with knee osteoarthritis. Archive of Physical Medicine and Rehabilitation, 91(9), 1447-1451. doi:10.1016/j.apmr.2010.06.002


46. Deones, V. L., Wiley, S. C., & Worrell, T. (1994). Assessment of Quadriceps Muscle Performance by a Hand-Held Dynamometer and an Isokinetic Dynamometer. Journal of Orthopaedic & Sports Physical Therapy, 20(6), 296–301. https://doi.org/10.2519/jospt.1994.20.6.296


Chapter 6

Measuring Quadriceps muscle strength in adults with severe or moderate intellectual and visual

disabilities: feasibility and reliability

Dijkhuizen, A., Douma, K. W., Krijnen, W. P., van der Schans, C. P., & Waninge, A. (2018). Journal of Applied Research in Intellectual Disabilities, 31(6),1083-1090.

doi: 10.1111/jar.12468.

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AbstractBackground A feasible and reliable instrument to measure strength in persons

with severe intellectual and visual disabilities (SIVD) is lacking. The objective elders

overall objective of our study was to determine feasibility, learning period and

reliability of three strength tests.

Methods Twenty-nine participants with SIVD performed the Minimum Sit-to-

Stand Height test (MSST), the Leg Extension test (LET) and the 30 seconds Chair-

Stand Test (30sCST), once per week for 5 weeks. Feasibility was determined by

the percentage of successful measurements, learning effect by using paired t

test between two consecutive measurements, test–retest reliability by intraclass

correlation coefficient and Limits of Agreement and, correlations between the

different tests by Pearson correlations.

Results A sufficient feasibility and learning period of the tests was shown.

The methods had sufficient test–retest reliability and moderate-to-sufficient

correlations.

Conclusion The MSST, the LET, and the 30sCST are feasible tests for measuring

muscle strength in persons with SIVD, having sufficient test re-test reliability.

Measuring Quadriceps muscle strength in adults with severe or moderate intellectual and visual disabilities:

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IntroductionMuscle strength contributes to mobility which impacts quality of life(1). The muscle

strength of lower limbs is important for ambulatory activities such as rising from

a chair, walking at an appropriate speed, and walking on stairs (2). Loss of muscle

strength may lead to a decrease of activities in daily living (ADL) (3). and worse

health-related quality of life (4). A weakness of the Quadriceps is a predictor of

mortality (5) as it is one of the first muscles that degenerates due to inactivity (6).

Muscle strength can be quantified by several reliable and valid tests that are

attuned for specific target populations. In various settings with adolescents to

older adults, with or without physical disabilities, it has been demonstrated that,

e.g., hand-held dynamometry (7,8,9,10) and the 1-repetition maximum (1RM) (11,12) are

reliable and valid methods quantifying muscle strength. The 1RM is considered to

be a reliable method for assessing leg muscle strength and its changes (13). The 30

seconds Chair-Stand test (30sCST) is a valid and reliable instrument in the general

population as well as in older adults (14) for measuring muscular endurance (15).

In addition, the 30sCST demonstrated a high validity for measuring Quadriceps

muscle strength (14). Related to the 30sCST is the Minimum- Sit-to- Stand Height

Test (MSST) which is used as a reliable functional instrument to measure strength

in lower limbs of older adults (16) and is an effective predictor for functional capacity (17).

For measuring muscle strength in persons with an intellectual disability (ID), a

hand-held dynamometry (16), the Jamar (18,19,20) (30sCST), and the 1RM (21) are used as

feasible and reliable instruments measuring muscle strength of Quadriceps muscle.

However, in persons with severe or profound ID, feasibility for measuring grip

strength (Jamar) is moderate to low (19). Therefore, this measurement instrument

does not seem to be feasible for people with severe intellectual and visual disability

(SIVD). Also, the hand-held dynamometry may not be applicable in persons with

a more severe intellectual disability. In addition, individuals experiencing SIVD

are physically weaker compared to persons with ID (22, 23). Persons with SIVD often

suffer from impaired health and physical fitness. Therefore, we expect persons

with SIVD to have low muscle strength like those individuals with ID, in particular

the Quadriceps muscle (24,25,26). However, until recently, a feasible and reliable

instrument to measure strength in persons with SIVD has been lacking.

Chapter 6

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Difficulties in performing strength tests can be expected due to severe ID and

visual impairments. Also, the time frame in which persons with SIVD learn to

adequately perform a strength test is currently unknown. The 1RM leg extension

(LET) does seem to be an appropriate instrument to measure Quadriceps muscle

strength in persons with SIVD due to the availability of the equipment and because

this test requires a movement in one fixed direction for the execution of the test.

The 30sCST and the MSST seem to be suitable instruments to measure strength

and endurance in persons with SIVD due to their required functional movement

which also occurs frequently during daily life.

Only a small number of measuring instruments to measure Quadriceps muscle

strength, described in literature, seems feasible for persons with SIVD, specifically,

the MSST, the LET, and the 30sCST due to their functionality and participants’

required cognitive ability. Hence, we have formulated the following research

questions. What is the feasibility, learning period, and reliability of the MSST, LET,

and the 30sCSTT for persons with severe intellectual and visual disabilities? What

is the association between scores of these tests?

MethodsParticipantsParticipants were recruited from a residential facility in the Netherlands. Inclusion

criteria consisted of having a moderate to severe (ID) according to the ICD-10

(27), visual disabilities (‘severely partially sighted to blind’; WHO, 2010), and Levels

I and II on the Gross Motor Function Classification System (GMFCS) (28,29). After

obtaining written consent from the representatives of the participants, participants

were screened regarding support for participation from a physician specialized in

intellectual disabilities in collaboration with a health care psychologist. Individuals

classified within GMFCS Levels I or II were included as a sufficient balance and

mobility is required to perform the tests. The GMFCS (28,29) is a five-level system

utilized to classify the severity of motor disabilities in persons with intellectual

and physical disabilities. Individuals classified as Level I are generally capable of

walking without restrictions but tend to have limitations in advanced motor skills.

Persons classified as Level II are capable of walking with minimal restrictions but

do not spontaneously increase their speed while walking. Persons classified as


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Level III are capable of walking only with the help of walking devices. The locomotor

skills of persons classified as GMFCS Levels IV or V are very limited; therefore, they

had to be excluded from the current study. Characteristics including gender, age,

level of ID, level of GMFCS, visual impairment, presence of a hearing impairment,

weight, and height were retrieved from the clients’ medical records. Data regarding

visual impairment were categorized as visual impairment or being blind. These

characteristics were determined and categorized by a physician specialized in

intellectual disabilities in collaboration with a health care psychologist.

Exclusion criteria consisted of mental or physical health issues that prevented

the client from participating such as psychoses, depression, or other severe

psychological problems such as behavioural and prolonged stress; somatic

diseases defined as chronic diseases and/or diseases that are not resolved in a

short period of time such as osteoarthritis, osteoporosis, pneumonia, and general

illness or fever; taking antibiotics, worsening of asthma or epilepsy as signified with

recent insult or epileptic fits, fresh wound(s)/bruise(s), or other factors causing

pain during movement, and finally, stress as evidenced by a participant’s behavior

shortly prior to the date of measurement.

Design This is a repeated measurements study to examine measurement properties of

three muscle strength measurements: The Minimum Sit-to-Stand Height Test

(MSST), the Leg Extension (LET), and the 30 seconds Chair-Stand (30sCST).

Participants performed the MSST, LET and 30sCST within one session once a week

for a period of five weeks. Prior to measuring, the test administrator completed a

checklist on all exclusion criteria. A test administrator and a gymnastics instructor

were present during the measurements. The latter was well informed on the

mental and physical limitations of each of the participants and was familiar to

the participants which facilitated the accuracy of the performance during testing

(30). The test administrator was a physical therapist or a bachelor student physical

therapy, familiar with the protocols of the strength tests. The tests were performed

in a fixed order whereby the 30sCST was measured first: the participant then

performed the LET; and, finally, the MSST. At least a one-minute pause was taken

between each performance of a test.

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108

Ethical statementThis study was performed in accordance with the guidelines of the Helsinki

Declaration (31). Dispensation was obtained from the legal Medical Ethics Committee (32). Because the participants were not able to, their legal representatives gave

informed consent. The measurements were performed in accordance with the

behavioral code section entitled ‘Resistance among people with an intellectual

disability in the framework of the Act Governing Medical-Scientific Research

Involving Humans’ (33). Consistent distress or unhappiness was interpreted as a

sign of a lack of assent, and further participation in the study was reconsidered.

Measurements Extra verbal instructions and encouragement were given to the participant during

the tests. Participants were also shown the expected movement and modelling

in order to ensure an accurate performance. This form of adapted guidance

was offered to maintain a minimal stress level for the participant because a

presence of SIVD and a possible additional hearing impairment make it difficult

or impossible for the participants to undergo measurements. If participants were

able to complete the tests according to the protocol, the test result was recorded

as ‘successfully performed’. When participants could not be present at time of

the measurements due to extenuating circumstances, ‘not present’ was recorded.

Measurements were defined as ‘not feasible’ if participants could not perform the

tests properly according to the protocol at the time of the measurements; e.g.,

when participants were unable to perform the test for cognitive reasons because

they did not understand the test; when participants wanted to get up/ raise by

using their hands or arms while performing the MSST and the 30sCST; and when

participants showed an incomplete lifting of the lower leg in the performance of

LET.

Minimum Sit-to-Stand Height Test (MSST)

The participant was asked to stand up from the lowest possible position to fully

upright without using his / her hands (without pushing off with arms/hands) or

widening their foot position outside the legs of the seat. This position was recorded

in centimeters. In order to rise from this deepest position, a special step less in-

depth-adjustable seat was developed. Below 18 cm, judo mats with a thickness


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6

of 4 cm were used. This allowed the seat depth to be reduced to 16 cm, 12 cm,

8 cm, 4 cm to eventually be phased to 0 cm when standing up from the floor.

The minimum sit-to-stand height test has an excellent reliability (ICC 0.91 (95%

confidence interval) CI 0.81; 0.96) and moderate responsiveness for an inpatient

rehabilitation setting (16)

Leg Extension test (LET)

The participant sat on appropriate fitness equipment to perform maximum leg

extension. Before performing the test, the maximum achievable extension (range

of motion) was recorded. We then asked the participant to fully extend the leg

against the maximum achievable resistance. The LET is a feasible and reliable

instrument for measuring muscle strength of Quadriceps muscle in adults with

ID (21).

30 seconds Chair-Stand test (30sCST)

The participant sat in a firm chair that had no arms. We asked the participant

to correctly stand up (full stance) and sit down as often as possible within a 30

second time frame without using his/her hands (without pushing off with hands)

and, when possible, with arms crossed over chest /over each other. Testing

time (30 seconds) was recorded using a hand-held stopwatch. The number of

completed standing incidents (up–down) was recorded. The 30sCST is developed

in a population of older adults and is highly correlated with strength of the lower

limbs (14). The 30sCST is a valid and reliable instrument in the general population (14) to measure muscular endurance (15). Feasibility and test-retest reliability was

moderate to good in adults with ID (ICC of 0.72 for same-day interval and 0.65

for a two-week interval) (18,19). Reliability and validity of the 30sCST in the general

elderly population is good with high test-retest reliability (r = 0.89) (14,34). Test–retest

reliability of the 30sCST in older adults with ID is moderate ICC 0.72 (same-day

interval) and 0.65 (two-week interval) (18).

Data analysesData analyses were performed using the Statistical Package for the Social Sciences

(SPSS 22).

Chapter 6

110

FeasibilityThe number of unsuccessful measurements (not feasible) was compared with

the total number of measurements to derive the percentage of all successful

measurements in order to determine feasibility. Feasibility was considered to be

sufficient if the percentage of successful assessments exceeded 85% (33,36,37).

Learning periodThe difference scores between consecutive time points of MSST, LET and 30sCST

measurements was subjected to the Shapiro-Wilk and the Anderson-Darling

normality tests. To gain insight into the learning period for the MSST, LET, and

30sCST, we used the paired t-test and the Wilcoxon signed rank test to investigate

whether there was a difference in means between two consecutive measurements

over a period of five weeks. A non-significant difference was considered as the end

of the learning period for a particular instrument.

Test re-test reliabilityBetween Weeks 4 and 5, test-retest reliability was analyzed by an intra-class

correlation coefficient (ICC, one way random) for the MSST, LET, and 30sCST where

an ICC ≥ 0.75 was considered to be acceptable (38,39). An ICC <0.75 indicated poor or

moderate, 0.75 - 0.90 good, and > 0.90 very good reliability (40). For the reference

range of the differences between the two measurements of the MSST, LET, and

30sCST, the limits of agreement (LOA) were calculated as ±1.96 timed the SD of

the difference. The LOA is considered to be an indicator of test-retest reliability

expressed in units of the measurement instrument as well as in a percentage of

the mean of the first test (38). To assess test-retest reliability, the Standard Error of

Measurement (SEM) was calculated for the MSST, LET, and 30sCST. The Standard

Error of Measurement (SEM) represents the standard deviation of measurement

error (40). The SEM reflects the reliability of the response (40).

Association between MSST, LET and 30sCSTTo investigate the degree in which the MSST, LE, and 30sCST measure the same

construct, the Pearson correlations (two-tailed) were calculated for Week 5.

Correlations of 1.0-0.9 are indicated as nearly perfect, 0.9-0.7 very large, 0.7-0.5


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6

large, 0.5-0.3 moderate, 0.3-0.1 small, and anything smaller than 0.1 trivial /very

small (41). We applied a principal components analysis (PCA) to the MSST, LET,

and 30sCST, to analyze the percentage of common variance between the three

measurements on the basis of their inter-correlations.

ResultsWritten consent was requested from the representatives of 75 candidates

whereby 44 agreed. Fifteen individuals were excluded for medical/behavioral

reasons. None of the participants were excluded from the study due to consistent

distress or unhappiness that was interpreted as a sign of a lack of consent. The 29

participants in this study comprise 16 males and 13 females. The mean (SD) age of

all of the participants was 38.7 (14.5) with a minimum age of 20 and a maximum

age of 63 (Table 1).

Table 1, Characteristics of the participants (N=29)

CharacteristicsGender, N (%)

Male

16 (55.2%)Age, Mean± SD 38.7 ±14.5

Intellectual disability, N (%)

Moderate

Severe

7 (24.1%)

22 (75.9%)GMFCS level, N (%)

Level I

Level II

25 (86.2%)

4 (13.8%)Visual Impairment, N (%)

(Severely) partially sighted

Blind

16 (55.2%)

13 (44.8%) Auditory Impairments, N (%)

Normal hearing

(Severely) hearing loss

Deaf

16 (55.2%)

11 (37.9%)

2 (6.9 %)Weight in kg, Mean ± SD 69.4 ±12.2Height in cm, Mean ± SD 167.4 ±12.8

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112

Feasibility The percentage of successfully performed MSST measures ranged between 86%

and 100%, for LET between 86% and 97%, and between 93% and 100% for 30sCST.

This indicates sufficient feasibility for the three different measurements.

Learning period The normality of the difference scores between consecutive time points of the

MSST, LET and, the 30sCST test, was rejected in all three tests. The parametric t-test

and the non-parametric Wilcoxon signed rank test gave comparable p-values.

Table 2 shows the mean (SEM) differences of the consecutive weeks, the t-values,

and the p-values corresponding to the paired differences in the mean. The size

of the differences in mean decreased for the sequential measurements. For the

MSST, a non-significant difference was determined between the measures of

Weeks 3 and 4. Regarding the 30sCST test, there was no significant difference

between measures Weeks 1 and 2 and, for the LET, a non-significant difference

was found between the measures of Weeks 4 and 5.

Test re-test reliability Table 2 summarizes the results of the (paired) t-tests and the Wilcoxon signed

rank tests, ICC analyses, the LOA, and the LOA as a percentage of the mean

between measurements of Weeks 4 and 5. Intra class correlation coefficients (one

way random) were very strong. The LOA, expressed as a percentage of the means

(LOA %), were ≤17.0 % for all three methods (MSST 6.7 %; LET 16.4 %; 30sCST 17.0

%). The standard error of measurement (SEM) was (0.12) for the MSST, (0.53) for

the LET, and (0.21) for the 30sCST.


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6

Tabl

e 2,

(Pai

red)

t-te

sts

(mea

sure

men

ts 1

-5),

Wilc

oxon

sig

ned

rank

test

(mea

sure

men

ts 1

-5),

ICC

anal

yses

, the

LO

A an

d th

e LO

A as

a p

erce

ntag

e of

the

mea

n fo

r MSS

T, L

ET a

nd 3

0sCS

T (m

easu

rem

ents

4-5

).

MSS

T (c

m)

Mea

n D

iff (S

EM)

tp

valu

e t-

test

Wilc

oxon

ICC

95%

CI

LOA

LO

A a

s m

ean

%

MSS

T 1-

2 1.

6 (0

.63)

2.5

0.02

0 / 0

.024

MSS

T 2-

31.

4 (0

.47)

3.1

0.00

4 / 0

.004

MSS

T 3-

40.

69 (0

.38)

1.8

0.08

5 / 0

.090

MSS

T 4-

50.

00 (0

.12)

0.0

1.00

0 / 1

.000

0.99

9*0.

997

– 0.

999

1.16

6.

7

LET

(kg)

Mea

n D

iff (S

EM)

TP

valu

eIC

C95

% C

ILO

A

LOA

as

mea

n %

LET

1

-2-2

.7 (0

.67)

-4.0

0.00

1 / 0

.001

LET

2-3

-3.1

(0.7

95)

-3.8

0.00

1 / 0

.001

LET

3-4

-2.6

(0.9

4)-2

.80.

011

/ 0.0

04LE

T

4-

5 -0

.17

(0.5

3)-0

.30.

747

/ 0.4

840.

973*

0.

939

– 0.

989

5.09

16

.4

30sC

ST (n

o)M

ean

Diff

(SEM

)T

P va

lue

ICC

95%

CI

LOA

LO

A a

s m

ean

%30

sCST

1-2

-0.6

8 (0

.53)

-1.3

0.20

8 / 0

.199

30sC

ST 2

-3

-0.2

3 (0

.39)

-0.6

0.56

3 / 0

.582

30sC

ST 3

-4

-1.1

(0.2

95)

-3.8

0.00

1 / 0

.001

30sC

ST 4

-5

-0.1

5 (0

.21)

-0.8

0.46

1 / 0

.448

0.96

7*0.

927

– 0.

985

1.96

17

.0

MSS

T: M

inim

um S

it-to

-Sta

nd h

eigh

t tes

t in

cent

imet

ers

(cm

), LE

: Leg

Ext

ensi

on e

xpre

ssed

in k

ilogr

ams

(kg)

, 30s

CST:

30

seco

nds

Chai

r St

and

test

exp

ress

ed in

num

ber

of r

epet

ition

s (n

o), S

EM: S

tand

ard

erro

r of

mea

sure

men

t, Co

rrel

atio

n is

sig

nific

ant a

t the

0.0

1 le

vel (

1-ta

iled)

.*P

valu

e <0

.001

Chapter 6

114

Figu

re 1

, Box

plot

s M

SST

wee

k 1-

5

F

igur

e 2,

Box

plot

s LE

T w

eek

1-5

F

igur

e 3,

Box

plot

s 30

sCST

wee

k 1-

5


115

6

The Box-and-whiskers plots in Figures 1, 2, and 3 visualize the measurements

obtained for the MSST, LE, and 30sCST over a period of five weeks.

Association between MSST, LET and 30sCST

A Pearson Correlation was computed in order to assess the association between

the MSST, LET, and 30sCST for Week 5. The correlation between the MSST and

30sCST was large (MSST-30sCST r = -0.56, p= 0.004), moderate between MSST and

LET (MSST-LET r = -0.31, p= 0.165) and moderate between LET and 30sCST (LET-

30sCST r = 0.45, p= 0.031). The principal components analysis (PCA) of the MSST,

LET and, 30sCST, revealed that 62% of the variance is explained by the the first

principal component.

Discussion The results show sufficient feasibility for the MSST, LET, and the 30sCST with an

acceptable learning period of a maximum of five practice sessions for individuals

with SIVD. Test re-test reliability is very good for all three methods in persons with

SIVD. The correlation between the MSST, LET, and 30sCST ranges from moderate

to large, suggesting that these instruments measure a different construct.

Our results indicate a sufficient feasibility for the MSST (86%-100%), LET (86%

and 97%), and 30sCST (93%-100%) for persons with SIVD. The MSST is a feasible

instrument for persons experiencing SIVD possibly due to its required functional

movement which often occurs during daily life. Feasibility of the LET is sufficient

which may be explained by the fact that the required movement was in one fixed

direction. Our 30sCST feasibility percentage is considerably better compared to

that found by Hilgenkamp and colleagues who found 44% feasibility of the 30sCST

in older adults with ID (18). In Hilgenkamp’s study participants performed seven

different physical fitness tests including the 30sCST. In our study, extra verbal

instructions and encouragement were given to the participants during testing by

gymnastic instructors who also demonstrated the movement expected from the

participants. This additional guidance could possibly have improved the feasibility

of the tests in our study. In our study, persons with profound ID were excluded,

and the mean age of the participants was younger than in the study of Hilgenkamp (18).

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Our results show a non-significant difference between the measures of Weeks 3

and 4 for the MSST that may indicate a learning period of at least four practice

sessions, which is one week (one session) shorter compared to the learning

period of the LET. As for the 30sCST, a non-significant difference was noticeable

from the first measures which could indicate the absence of a learning period.

For persons with SIVD, the MSST, and the 30sCST appear to be easier to perform

than the LET possibly because of the required functional movement in both

measurements. The LET requires a coordinative difficult movement, and it is not

a functional test. Therefore, we already expected that the LET would be the most

difficult test to perform for those experiencing SIVD. The learning periods we

found were in accordance with those of other performance tests in persons with

SIVD, for example, five practice sessions were performed to become familiar with

a modified Berg Balance Scale (36). In another study of Waninge and colleagues in

which persons with SIVD performed the six minutes walking distance at relatively

short intervals, a learning period of two weeks was required (23). It is possible

that the learning period of the present study could be decreased if the training

sessions were planned closer to each other. The participants in our study seemed

to be capable of performing the 30sCST well with the given instructions and

guidance from the first measurement, which could indicate that persons with SIVD

can perform the 30sCST well without the need of a learning period. The possible

absence of a learning period for 30sCST seems to be in line with the findings of

Hilgenkamp who found no statistically significant learning effect in the test results

of 30sCST between their practice session and their first measurement (18). Also, the

means in our study are not less than those determined by Hilgenkamp (18).

Due to the limitations of persons with SIVD, it was necessary to adapt the guidance

of the participants during testing in the sense of some extra standardized verbal

instructions, encouragement, and demonstrating the expected movement

and modelling to the participant during the test in order to achieve optimal

performance. These additional instructions ensured that participants kept their

arms crossed over the chest during the performances of the MSST and the 30sCST.

Also, encouragement was provided by counting out loud while participants

performed the 30sCST to ensure that they did not stop prior to the end of the

30sCST. This support was also offered to maintain the most minimal stress level

as possible for the participant. In some cases, the test instructor indicated that


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the limit had been reached concerning the mental capacity of the participant to

maintain a minimal stress level. To decrease the influence of differences in these

limits, the gymnastics instructors were all instructed in the same manner and were

well-informed of the test protocols prior to the measurement period.

The test re-test reliability for the MSST, the LET, and the 30sCST is very good in

persons experiencing SIVD. This accords with the findings of Schurr regarding the

MSST (16) and Hilgenkamp concerning 30sCST (18). Moreover, our results showed

that LOA, expressed as a percentage of the means, were less than or equal to

17% for all three methods. In general, higher LOA’s are found in performance

tests when compared to non- performance testing such as, for example, BMI

measurements. Our LOA’s are in line with the findings of Waninge who found a

sufficient test-retest reliability for the a Shuttle Run test (LOA% = 23%), and for

the 6Minute Walking Distance (LOA% = 30%) in persons with SIVD (23). Taking into

account the limited abilities of persons with SIVD to perform measurements, in

general, and the required level of intelligence, concentration, and coordination to

perform the MSST, the LET, and the 30sCST well, we consider the LOA expressed as

a percentage sufficient for these methods. Hence, we consider that the reliability

is sufficient for the MSST, LET, and 30sCST in persons with SIVD.

A significant correlation was determined between the MSST and the 30sCST, a

moderate correlation between the MSST and the LET, and a moderate correlation

between the LET and the 30sCST. It seems that our finding concerning the

correlation between LET and MSST is in line with findings of Schurr and colleagues

who ascertained that 8-17% of the variability in the MSST was explained by

the strength of the Quadriceps muscle (16). Apparently, performance of MSST is

influenced by factors other than knee extensor muscle strength (16). In our study, a

number of participants had achieved their maximum depth while performing the

MSST; however, they were able to repeat the test several times from this maximum

depth. This could indicate that the participant’s mobility or agility was the limiting

factor instead of muscle strength. It appears that all three methods actually

measure different aspects, e.g., the MSST for agility and strength, the LET for

strength, and the 30sCST for muscle endurance with which they could complement

one another. However, the PCA to the MSST, LET and, 30sCST, revealed that 62%

of the variance is common. Therefore, the first principal component (strength)

explains a relatively large amount of variance. Clinically, the tests seem to be

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partly complementary (a view sustained by our PCA). Therefore, we recommend

that when the Quadriceps muscle strength is the primary outcome for a training

program, then the LET test as a measuring instrument would be legitimate to

use in persons with SIVD. If, however, functional aspects such as measuring and

mapping the performance or level of ambulatory activities, are deemed important,

then the MSST (flexibility and strength) and / or 30sCST (muscle endurance and

strength) are of added value and therefore the tests might be used as a test-set to

gain insight into clients’ ambulatory abilities and their need for support.

A limitation of this study is that, due to the exclusion criteria implied by the research

question, only a rather small number of participants could be included. The

objective of the study was to explore if the tests developed for persons with SIVD,

would be feasible and reliable. In this study, the measurements were repeated

every week over a period of five weeks. This frequency per week was expected to

be too intensive for persons with profound intellectual disability. Therefore, they

were excluded implying a smaller sample size. Nevertheless, this study provides

extensive statistical analyses to firstly explore the feasibility and reliability of

the measurements and secondly to investigate the correlation between the

measurements, for persons with SIVD. A follow-up study should objective at

providing further evidence concerning the feasibility and reliability of the results in

a larger more heterogeneous group. Therefore, further research of the feasibility

and reliability in persons with less severe and more severe intellectual disabilities,

and both with and without additional visual impairment is recommended to be

able to better generalize the results for a broader target group.

In conclusion, the MSST, the LET, and the 30sCST are feasible methods with an

acceptable learning period and a sufficient test re-test reliability for persons with

SIVD.


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14. Jones, C. J., Rikli, R. E., & Beam, W. C. (1999). A 30-s chair stand test as a measure of lower body strength in community-residing older adults. Research Quarterly for Exercise and Sport, 70(2), 113-9. doi: 10.1080/02701367.1999.10608028

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23. Waninge, A., Evenhuis, I. J., van Wijck, R., & van der Schans, C. P. (2011c). Feasibility and Reliability of Two Different Walking Tests in People with Severe Intellectual and Sensory Disabilities. Journal of Applied Research in Intellectual Disabilities, 24(6), 518-527 10. https://doi.org/10.1111/j.1468-3148.2011.00632.x

24. Horvat, M., Croce, R., Pitetti, K. H., & Fernhall, B. (1999). Comparison of isokinetic peak force and work parameters in youth with and without mental retardation. Medicine and Science in Sports and Exercise, 31(8), 1190-5. doi: 10.1097/00005768-199908000-00017

25. Angelopoulou, N., Tsimaras, V., Christoulas, K., Kokaridas, D., & Mandroukas, K. (1999). Isokinetic knee muscle strength of individuals with mental retardation, a comparative study. Perceptual and Motor Skills, 88(3), 849-55. doi: 10.2466/pms.1999.88.3.849

26. Borji, R., Sahli, S., Zarrouk, N., Zghal, F., & Rebai, H. (2013). Neuromuscular fatigue during high-intensity intermittent exercise in individuals with intellectual disability. Research in Developmental Disabilities, 34(12), 4477-84. doi: 10.1016/j.ridd.2013.09.025

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29. Gorter, J. W. (2001). Gross Motor Function Classification System (Dutch translation), Utrecht: Revalidatiecentrum De Hoogstraat

30. Hale, L., Bray, A., & Littmann, A. (2007). Assessing the balance capacities of people with profound intellectual disabilities who have experienced a fall. Journal of Intellectual Disability Research, 51(4), 260-8. doi: 10.1111/j.1365-2788.2006.00873.x

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35 . Enkelaar, L., Smulders, E., van Schrojenstein Lantman-de Valk, H., Weerdesteyn, V., & Geurts, A. C. H. (2013). Clinical measures are feasible and sensitive to assess balance and gait capacities in older persons with mild to moderate Intellectual Disabilities. Research in developmental disabilities, 34 (1), 276–285. doi: 10.1016/j.ridd.2012.08.014

36. Waninge, A., van Wijck, R., Steenbergen, B., & van der Schans, C. P. (2011). Feasibility and reliability of the modified Berg Balance Scale in persons with severe intellectual and visual disabilities. Journal of Intellectual Disability Research, 55(3), 292-301. doi: 10.1111/j.1365-2788.2010.01358.x

37. Waninge, A., Rook, R. A., Dijkhuizen, A., Gielen, E., & van der Schans, C. P. (2011b). Feasibility, test-retest reliability, and interrater reliability of the Modified Ashworth Scale and Modified Tardieu Scale in persons with profound intellectual and multiple disabilities. Research in Developmental Disabilities, 32(2), 613-20. doi: 10.1016/j.ridd.2010.12.013

38. Bland, J. M., & Altman, D. G. (1986). Statistical methods for assessing agreement between two methods of clinical measurement. The Lancet, 8, 307-310

39. Lee, J., Koh, D., & Ong, C. N. (1989). Statistical evaluation of agreement between two methods for measuring a quantitative variable. Computers in Biology and Medicine, 19(1), 61-70. doi: 10.1016/0010-4825(89)90036-x

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Chapter 7

General Discussion

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General DiscussionReference valuesGenerally, muscle strength values are compared with reference values without

taking ethnic, geographic, or cultural backgrounds into consideration. Reference

values used in the Netherlands for adults are based on populations in the USA

obtained 20 years ago. Reference values for children based on a Dutch population

are also 20 years old. In Chapter 2 and Chapter 3, reference values for muscle

strength for the Dutch adult population between 20 and 60 years of age and

for children between 8 and 18 years of age were generated using a hand-held

dynamometer. The obtained values of were stratified by age and gender and were

compared with those of the earlier Dutch and USA values.

AdultsMuscle strength was influenced by several participant characteristics. Regression

analyses indicated that weight, height, and male gender had a positive effect on

strength while increasing age and female gender had a negative effect; these

effects have also been found in other studies (1,2). The predictive value of the

characteristics was moderate to low. The comparison of muscle strength values

found in this thesis and those of the USA (2) revealed significant differences

between the two populations. The USA values were generally higher for the lower

extremity compared to the Dutch values for males and females. For males, values

for the upper extremity were similar between both groups, however, for Dutch

females, they were higher except for shoulder abduction. While reliability of the

measurements was excellent, the limits of agreements (LOA) were substantial and

intensified with increasing strength.

ChildrenSimilar to adults, muscle strength in children was also influenced by weight,

height, age, and gender as was found previously (1,2,3,4,5,6). Boys become stronger

than girls from 15 years of age, similar to what was found in other studies (5,6).

Particularly height had a strong effect on elbow flexion strength whereas weight

had a strong effect on knee flexion and extension strength. The predictive value

of the characteristics was moderate. In an earlier study in Dutch children, (6) higher

General Discussion

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values were determined for 29 of the 72 outcomes while, in an earlier study in

Chilean children, (5) lower values were found for all ages. Similar to the results of

adults, measurements were reliable but LOA were quite substantial. The results of

Chapters 2 and 3 showed that reference values for muscle strength for adults and

children are region and time specific and should therefore be updated regularly

within specific geographical areas. Differences between the prior Dutch study (6) and the current study may be explained by less active lifestyles in the last 20

years (7,8). Differences between the Chilean and current study can be explained by

a substantially higher weight in the Dutch children.

The Q ForceIn Chapter 4, a new mobile instrument for measurement of the isometric

Quadriceps muscle was introduced, i.e., the Q Force. It was developed as an

alternative for non-mobile instrument-held, dynamometers and mobile hand-held

dynamometers. The objective was to develop a mobile instrument with improved

precision compared to existing instruments. It was designed to measure isometric

Quadriceps muscle strength in various degrees of extension and provides

numeral and graphic information about the generated strength and course of

the contraction. Measurements were reliable, however, the LOA were relatively

large. Measurements on the second day resulted in higher values than those on

the first day. Such an increase was also found in measurements performed with

instrument held dynamometers, suggesting a learning effect of the participants (9,10,11). The reliability of the Q Force was comparable with that of other instruments;

however, the weight and size of the Q Force limit its mobile applicability.

Repeated Quadriceps muscle strength measurements in older adultsIn Chapter 5, the effects of repeated muscle strength measurements were studied

in older adults. No significant effect for repetitions within days or between days

was found except for Quadriceps muscle strength (right side) between day

1 and day 3. Learning effects that were determined in Chapter 5 could not be

confirmed statistically. However, for the right leg, small, insignificant increases

in strength were ascertained between repetitions and between days. Hence, a

small learning effect might be present that could probably not be detected due

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to measurement variation. The outcomes of the left leg were fairly constant.

This left/right difference cannot be explained satisfactorily. Since the majority

of the people is right dominant, this learning effect can possibly be attributed to

improved coordination. A future study in a larger sample of older persons might

demonstrate a learning effect more clearly. The current findings, however, indicate

that a single measurement is sufficient for quantifying muscle strength groups for

older adults.

Quadriceps muscle strength measurements in adults with moderate or severe intellectual and visual disabilitiesIn Chapter 6, the feasibility, learning period, and reliability of three tests, the

Minimum Sit to Stand Test (MSST), Leg Extension Test (LET) and 30 Seconds Sit

to Stand Test (30sCST), was studied in subjects with severe intellectual and visual

disabilities (SIVD). All tests were feasible, the learning period was 0 to 5 weeks, and

reliability was excellent. Correlations between the tests were moderate indicating

that each test measured a different construct. Additionally, in this study, a learning

effect was present. The learning period up to 5 weeks and was considerably longer

than the 1 to 2 weeks found in the study of Chapters 4 and 5 but can possibly

be explained by the intellectual and motoric capacities of the tested population.

The results indicate that simple strength measurements are possible and reliable

in adults with severe intellectual and visual disabilities. The LOA were moderate

and varied between 6.7% of the measured value for the MSST and 17.0% for the

30sCST.

Reliability of strength measurementsOverall, the previous chapters showed that muscle strength can be measured

reliably on a group level. The explained variance of the regression analyses ranged

from 25-66% indicating that additional factors other than age, gender, weight,

and height play a role in statistically predicting muscle strength, for example, the

degree of physical activity during the day and the type of sport and/or hobby.

These factors might cause measurement variation since substantial LOA’s were

found in all studies. A variation in measurement results may be attributed to

variation in coordination or fatigue of the tested subject, fear of maximal effort,

learning effects, or variation of the tester in conducting the tests (12,13,14). The results

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of Chapters 4 and 6 and, to a much lesser extent, Chapter 5, suggest a learning

effect. Taking the above into account, for a precise estimate of muscle strength

measurements on an individual level, they should be performed 3 times.

Strength and activities of daily lifeReference values allow clinicians to make informed decisions based on the

comparison. When an individual strength falls within the range of normal strength,

it might be assumed that this strength is sufficient for executing normal functions

at an acceptable level. To quickly determine if an individual’s strength falls within

the normal range and based on our studies, the app “MuscleNorm” has been

developed.

Figure1, MuscleNorm

In the app, the independent variables can be can be entered in the home screen,

the measured muscle can be selected, and the acquired values can be entered.

The app provides a graphic representation of the acquired value compared to

the mean predicted values and the 95% CI of the Dutch and/or USA reference

values. The app is available in the Google Play and Apple App store. It is possible,

however, that an individual with normal muscle strength perceives limitations in

activities of daily life. Bodyweight, coordination, endurance, or the desired level of

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activities may limit the performance of these activities in daily life. Hence, solely

taking muscle strength measurements does not provide sufficient information to

translate these simply into performance of activities of daily life. Functional tests

closely resembling movements executed during activities of daily living, such

as the 1-minute sit to stand test, may provide additional insight into functional

capacity. Additionally, a Functional Capacity Evaluation which that a battery of

tests, observations, and practical activities to evaluate an individual’s physical

ability to function in different areas may provide insight into the performance of

activities in daily life. Additionally, questionnaires can be used to gain insight into

perceived functional limitations. It is therefore recommended that physiotherapists

combine tests with functional tests and questionnaires in their assessment of

muscle strength.

Strength, weight, and functionMuscle strength, as already mentioned, cannot be translated directly into the

daily functioning of individuals since daily functioning is at least partly dependent

on body weight. Body weight is particularly important since it has increased

considerably in the Western world in the last decades. (8,9,10,11) Individuals with

the same Quadriceps muscle strength but with a different bodyweight may have

dissimilar functional capacity and may not even be able to perform the same

tasks. Maximum oxygen uptake (VO2 max) does take bodyweight into account as

it is expressed in milliliters per minute per kilogram uptake. This method provides

a more accurate representation of the capacity to perform activities in daily life

or sports as it relates to the uptake capacity to the bodyweight of the individual.

An indicator that takes strength and bodyweight into account seems a step forward

in determining the functionality of the available strength. A simple strength to

weight ratio relating Quadriceps muscle strength in Newton to bodyweight in kg

may provide such a type of information and is expressed as (15,16,17) in

terms of Newton strength per Kilogram bodyweight. Further research may focus

on this ratio to determine its usefulness in clinical decision making.

Strength and endurance This thesis focused on measuring maximal isometric strength. The majority of

activities of daily life require only a limited percentage of maximum available

General Discussion

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7

strength, however, that amount must be repeatedly available. For example, for a

half hour of brisk walking, an individual takes about 3500 steps which means that

the muscles involved have to contract 3500 times, i.e., approximately two times

per second. This number of contractions requires muscular endurance. It might

be assumed that, if muscle strength is sufficient, then muscle endurance might

also be sufficient and, when muscle strength is reduced, then endurance will also

be reduced. However, muscle strength and muscle endurance do not decrease to

the same extent (18). Thus, muscle endurance may decrease unnoticed, resulting in

unexpected limited activities of daily life. It is therefore recommended to measure

both muscle strength and muscle endurance in frail people or subjects that have

limitations in activities of daily life.

Monitoring muscle strength In this thesis, muscle strength measurements were performed at a specific point

in time. Muscle strength is generally measured at the beginning and end of a

rehabilitation program to evaluate changes over time. With advancing age or in the

presence of a chronic disease monitoring, muscle strength is also important since

it may decline over time. Decreased muscle strength and endurance are directly

and strongly related to a reduction in activities of daily life and an increase in

falls (19,20,21). Several other health related factors are monitored regularly over time

such as blood pressure or bodyweight which are both predictors of cardiovascular

diseases, diabetes, and mortality. Considering this, muscle strength and endurance

should be monitored regularly over time also in older persons or the chronically ill.

Implications Clinically, muscle strength measurements begin with an assumed muscle

weakness in a patient based on patient history, questioning of the patient, clinical

intuition, and experience. Based on the previous, a hypothesis is subsequently

formulated. Physical testing confirms or rejects this hypothesis. The advantage

of an instrumental muscle strength measurement is that it provides objective

evidence and quantification of strength. Muscle strength measurements involve

two persons: the tester and the tested. Performing a clinical measurement involves

mastering the practical skill. The skills of muscle strength measurements using a

hand-held dynamometer is practiced sufficiently during the physiotherapy study.

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Starting professionals are therefore technically able to measure muscle strength

using a hand-held dynamometer. However, attention should also be paid to the

quality of the measurement and factors influencing the measurement outcome.

Was the contraction maximal? Was the measurement break or make performed

correctly without compensation of the participant? Additionally, it should be

evaluated whether the observed range of outcomes of repeated measurements

is in accordance with the expectation. If the range of outcomes in repeated

measurements is too wide, the measurement should be repeated with sufficient

recovery time between repetitions or at another measurement day in order to

prevent fatigue. Further, measurement results should be put into perspective, not

merely an evaluation relative to reference values but also with regard to perceived

limitations in activities of daily life. Taking these factors into account will help to

interpret outcomes of muscle strength measurements.

Living databasesReference values, as generated in this thesis, are utilized in databases for

comparison of outcomes of individual muscle strength measurements. These

reference values are often used for years. The values found in Chapters 2 and 3

differed from those that were previously determined suggesting that reference

values are valid for a certain period of time in a certain region. These values should

therefore be regularly adjusted on the basis of new measurements, so called

“living databases”. These databases should be updated with anthropometric data

and values obtained from measurements at work, in health monitoring projects

in adults, in movement programs for older persons, and in school health projects

for children. Statistical programs can continuously process the newly added

values in the database. In this way, reference values become a valid reflection of a

population in a certain time period.

Methodological considerationsIn this thesis, convenience sampling was applied, and samples were small relative

to the populations for which they were intended, possibly inducing some selection

bias. Therefore, the outcomes of the studies may not be representative for the

intended populations. However, the populations contributing to the references

values were drawn from different socio-economic backgrounds in the Netherlands,

General Discussion

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7

both urban and rural. Reliability coefficients of the studies were similar to those

of other studies. We therefore assume no systematic deviations in the measured

values are present, and the reference values found in this thesis can be used

clinically (1,2,3,4). A comparison of strength values of this thesis with other studies is

difficult since strength, as shown, is time and region specific. Additionally, lifestyle,

activity levels, and body mass index change over time and differ per region (8).

The distribution of strength across age groups and the effects of age, gender,

height, and weight on strength are similar to other studies (1,2,3,4). Hence, strength

is time and region specific but characteristics of participants to predict strength

are similar.

Another factor that might have influenced the outcomes in Chapters 2 and 3

is the substantial number of physiotherapy students that acted as observers.

Several studies indicated that strength and weight of the observer and experience

of participant influence the outcomes of measurements (45,47). The large

number of observers and variation in strength and weight may have led to an

increase in measurement variation. Despite this variation, it is possible that an

underestimation of one observer might be compensated by an overestimation

of another observer and lead to a correct estimate of a group mean. Based on

the outcomes of this thesis, in particular the distribution of strength over the age

groups and similar influence of factors associated with strength, it is most likely

that the reference values presented are a valid reflection of the population for

which they are intended. The results of the studies can be used in clinical practice

because of the above.

In Chapter 4 and Chapter 5, a small convenience sample of healthy older adults

participated. Although a clear learning effect was found in Chapter 4 and not

in Chapter 5, it is unclear to what extent those results can be generalized to

populations other than the tested participants, e.g. older adults with a chronic

disease. It is plausible that learning effects differ between such sub-populations.

In Chapter 6, the feasibility, learning period, and reliability of three tests was

studied in a small sample of adults with severe intellectual and visual disabilities.

All tests proved to be feasible with an acceptable learning period and a sufficient

test retest reliability. However, results can be generalized to a limited extent

considering the small sample and the selection of participants. Confirming the

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results by comparing these with similar studies is not possible since this is the

first study to explore the feasibility and reliability of strength measurements for

persons with SIVD. Future studies with a larger sample should confirm the findings

of Chapter 6.

ConclusionsMuscle strength differs between regions and changes over time within the

same region when these are based on physical activity level, type of physical

activity, and food intake. Muscle strength can be measured reliably in different

populations, however, the LOA are substantial. Consequently, strength should

change considerably in order to be determined which causes decision making on

an individual level to become uncertain with respect to smaller differences.

Recommendations for further researchFuture research should focus on improving measurement precision by improving

protocols and/or observer quality, for example, by determining the influence of

skill or strength training of the observer on measurement variation; developing

a strength-to-bodyweight index for frail people and subjects with limitations in

activities of daily life; and developing early detection methods such as population

studies and screening programs to early detect decreased muscle strength.

General Discussion

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7

References1. Bohannon, R. W. (1997) Reference values for extremity muscle strength obtained by

hand-held dynamometry from adults aged 20 to 79 years. Archives of Physical Medicine and Rehabilitation, 78(1), 26–32. https://doi.org/10.1016/s0003-9993(97)90005-8.


3. Eek, M. N., Kroksmark, A.K., & Beckung, E. (2006). Isometric Muscle Torque in Children 5 to 15 Years of Age: Normative Data. Archives of Physical Medicine and Rehabilitation, 87(8), 1091–1099. https://doi.org/10.1016/j.apmr.2006.05.012.


5. Escobar, R. G., Munoz, K. T., Dominguez, A., Banados, P., & Bravo, M. J. (2016). Maximal isometric muscle strength values obtained By hand‎held dynamometry in children between 6 and 15 years of age. Muscle & Nerve, 55(1), 16–22. https://doi.org/10.1002/mus.25180.

6. Beenhakker, E. A. C., van der Hoeven, J. H., Fock, J. M., & Maurits, N. M. (2001). Reference values of maximum isometric muscle force obtained in 270 children aged 4–16 years by hand-held dynamometry. Neuromuscular Disorders, 11(5), 441–446. https://doi.org/10.1016/s0960-8966(01)00193-6.

7. Al Hazzaa, H.M. (‎2004)‎. Prevalence of physical inactivity in Saudi Arabia: a brief review. EMHJ - Eastern Mediterranean Health Journal, 10 (‎4-5)‎, 663-670. https://apps.who.int/iris/handle/10665/119465

8. Schönbeck, Y., Talma, H., van Dommelen, P., Bakker, B., Buitendijk, S. E., HiraSing, R. A., & van Buuren, S. (2011). Increase in Prevalence of Overweight in Dutch Children and Adolescents: A Comparison of Nationwide Growth Studies in 1980, 1997 and 2009. PLoS ONE, 6(11), e27608. https://doi.org/10.1371/journal.pone.0027608.

9. World Health Organisation. (2020) Obesity and overweight. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight

10. World Health Organization. (2021). Data and statistics. https://www.euro.who.int/en/health-topics/noncommunicable-diseases/obesity/data-and-statistics

11. Ogden, C. L., Carroll, M. D., Kit, B. K., & Flegal, K. M. (2012). Prevalence of Obesity and Trends in Body Mass Index Among US Children and Adolescents, 1999–2010. JAMA, 307(5), 483. https://doi.org/10.1001/jama.2012.40

12 . Kienbacher, T., Kollmitzer, J., Anders, P., Habenicht, R., Starek, C., Wolf, M., Paul, B., Mair, P., & Ebenbichler, G. (2016). Age-related test-retest reliability of isometric trunk torque measurements in patiens with chronic low back pain. Journal of Rehabilitation Medicine, 48(10), 893–902. https://doi.org/10.2340/16501977-2164

13. Ritti-Dias, R. M., Basyches, M., Câmara, L., Puech-Leao, P., Battistella, L., & Wolosker, N. (2010). Test-retest reliability of isokinetic strength and endurance tests in patients with intermittent claudication. Vascular Medicine, 15(4), 275–278. https://doi.org/10.1177/1358863x10371415

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14. Scott, D. A., Bond, E. Q., Sisto, S. A., & Nadler, S. F. (2004). The intra- and interrater reliability of hip muscle strength assessments using a handheld versus a portable dynamometer anchoring station. Archives of Physical Medicine and Rehabilitation, 85(4), 598–603. https://doi.org/10.1016/j.apmr.2003.07.013.



17. Jenkins, N. D. M., & Cramer, J. T. (2017). Reliability and Minimum Detectable Change for Common Clinical Physical Function Tests in Sarcopenic Men and Women. Journal of the American Geriatrics Society, 65(4), 839–846. https://doi.org/10.1111/jgs.14769.

18. Barbat-Artigas, S., Rolland, Y., Cesari, M., Abellan van Kan, G., Vellas, B., & Aubertin-Leheudre, M. (2012). Clinical Relevance of Different Muscle Strength Indexes and Functional Impairment in Women Aged 75 Years and Older. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 68(7), 811–819. https://doi.org/10.1093/gerona/gls254

19. Ryder, J. W., Buxton, R. E., Goetchius, E., Scott-Pandorf, M., Hackney, K. J., Fiedler, J., Ploutz-Snyder, R. J., Bloomberg, J. J., & Ploutz-Snyder, L. L. (2012). Influence of muscle strength to weight ratio on functional task performance. European Journal of Applied Physiology, 113(4), 911–921. https://doi.org/10.1007/s00421-012-2500-z

20. Newman, A. B., Kupelian, V., Visser, M., Simonsick, E. M., Goodpaster, B. H., Kritchevsky, S. B., Tylavsky, F. A., Rubin, S. M., & Harris, T. B. (2006). Strength, But Not Muscle Mass, Is Associated With Mortality in the Health, Aging and Body Composition Study Cohort. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 61(1), 72–77. https://doi.org/10.1093/gerona/61.1.72

21. Hasan, N. A. K. A. K., Kamal, H. M., & Hussein, Z. A. (2016). Relation between body mass index percentile and muscle strength and endurance. Egyptian Journal of Medical Human Genetics, 17(4), 367–372. https://doi.org/10.1016/j.ejmhg.2016.01.002

22. Scott, D., Stuart, A. L., Kay, D., Ebeling, P. R., Nicholson, G., & Sanders, K. M. (2014). Investigating the predictive ability of gait speed and quadriceps strength for incident falls in community-dwelling older women at high risk of fracture. Archives of Gerontology and Geriatrics, 58(3), 308–313. https://doi.org/10.1016/j.archger.2013.11.004

23. Muehlbauer, T., Besemer, C., Wehrle, A., Gollhofer, A., & Granacher, U. (2012). Relationship between Strength, Power and Balance Performance in Seniors. Gerontology, 58(6), 504–512. https://doi.org/10.1159/000341614

24. Daubney, M. E., & Culham, E. G. (1999). Lower-Extremity Muscle Force and Balance Performance in Adults Aged 65 Years and Older. Physical Therapy, 79(12), 1177–1185. https://doi.org/10.1093/ptj/79.12.1177

General Discussion

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7

Summary

Summary

138

SummaryMuscle strength is an important determinant for physical performance in activities

of daily living, work, or sports. To determine if strength of an individual is normal or

has decreased, obtained values can be compared to reference values. Reference

values used in the Netherlands, however, were either obtained 20 years ago or

were from the USA. It is not clear if these values can be used in clinical practice or

can be generalized to other populations. In general, the current protocols used

to determine strength apply 1 to 3 measurements on a single day. It is not clear

how precise these protocols estimate maximum muscle strength. For example,

protocols using more repetitions could lead to higher outcomes due to learning

effects or to lower values due to fatigue. Muscle strength can be reliably and

precisely measured using hand-held dynamometry but variations in measurement

results within a person are substantial. Mobile instruments reducing that variation

are needed. Strength can be reliably measured in different populations and

settings, however, it is unclear if strength measurements are feasible and reliable

in individuals with severe intellectual and visual disabilities. In Chapter 1, the

topics of research of this thesis are introduced and the objectives are described.

As already described above, reference values for adults used in the Netherlands

were obtained 20 years ago in the USA. It is not clear if these values can still be

utilized in clinical practice or generalized to the Dutch population. The objectives as

described in Chapter 2 were to first determine reference values for a population of

Dutch workers; second, to compare these values with those of a USA population;

and, third, to analyze and confirm the reliability of hand-held dynamometers for

isometric strength measurements. In total, 462 healthy working subjects (259 male,

203 female) were included. Their age ranged from 20 to 60 years with a mean (SD)

of 41 (11) years. Muscle strength values from elbow flexion and extension, knee

flexion and extension, and shoulder abduction were obtained using a MicroFet

2 hand-held dynamometer. The break method was applied and measurements

were repeated three times in a single occasion. Muscle strength expressed in

Newton, means (SD), and confidence intervals were determined for males and

females in age groups ranging from twenty to sixty years old. Regression equations

and explained variances were calculated from weight, height, gender, and age.

The mean values and 95% CI were compared to the results from other studies.

Reliability was analyzed by calculating the intraclass correlation coefficients (ICC)

Summary

139

and limits of agreement (LOA).

The explained variance of the regression analyses ranged from 0.25 to 0.51.

The comparison of muscle strength data of the Dutch population with that of

the USA revealed important differences. Males in the USA studies possess more

strength than those of the current study except for elbow flexion, dominant

and non-dominant, in which only the age group 50–59 years exhibited greater

values. Females in the USA studies exhibit less strength in elbow flexion and

extension than those in the current study with the exception of elbow extension,

non-dominant for age group 30 to 39 and 50 to 59 years. However, strength of

shoulder abduction, knee flexion and extension indicated greater values in the

USA studies, except for shoulder abduction of the non-dominant side in age group

20 to 29 years.

Reliability was excellent, and the ICCs ranged between 0.83 to 0.94. The LOA

were substantial and ranged from 37.3 to 117.8 Newton. Based on this study,

reference values and regressions equations were made available. It is concluded

that reference values differ between the Netherlands and the USA. Additionally,

regression equations can only partly predict muscle strength.

Reference values for children used in the Netherlands were also obtained 20 years

ago. It is not clear if these reference values can still be used in clinical practice. It is

also not clear whether reference values drawn from the Dutch population can be

generalized to other populations. The objectives as described in Chapter 3 were to

first determine reference values for a population of children and compare those

with previously Dutch reported values and recently reported Chilean values; and,

second, to statistically predict muscle strength from weight, height, gender, and

age. In total 1,252 subjects, 594 and 658 boys, mean (SD) age 13.0 (2.4) years,

were included. Muscle strength values from elbow flexion and extension, knee

flexion and extension, and shoulder abduction were obtained using a MicroFet 2

hand-held dynamometer. The break method was applied and each measurement

was repeated three times. Muscle strength was expressed in Newton, means (SD)

and 95% confidence intervals were calculated for boys and girls ranging from 8

to 17 years stratified by age. Regression equations and explained variances were

calculated from weight, height, gender, and age. The mean values and 95% CI

were compared to the results from previous studies. Reliability was analyzed by

Summary

140

calculating the ICCs and LOA.

The explained variance (R2 adjusted) of the regression analyses ranged from 0.46

to 0.66. Muscle strength in the current Dutch study was lower in 29 of the 72

comparisons in relation to the results of the prior Dutch study published in 2001.

Differences ranged from 1 Newton in elbow extension for females of 9 years of

age of age to 187 Newton for knee flexion in boys 16 years of age. Compared to

a Chilean study published in 2016, Dutch children were systematically stronger

in all age and muscle groups ranging from 15 Newtons in boys 11 years of age to

217 Newtons for knee extension in boys 15 years of age. Reliability was excellent,

and the ICC coefficients ranged from 0.80 and 0.95. The LOA were substantial and

ranged from 44 Newton for right elbow extension to 101 Newton for right knee

extension which corresponded with 21% and 36% of the mean measured values,

respectively. Based on this study, reference values and regressions equations

were made available. It is concluded that reference values differ in time and

between countries. Additionally, regression equations can only partly predict

muscle strength.

Strength can be measured reliably using mobile instruments. However, instruments

which are more precise are required to reduce the LOA. The Q Force is a new

and innovative mobile instrument for measurement of the isometric muscle. The

objective as described in Chapter 4 was to determine the test-retest reliability of

isometric Quadriceps muscle strength measurements using the Q Force in older

adults. In total, 41 healthy older adults, 13 males and 28 females with a mean (SD)

age 81.9 (4.89) years, were included. The isometric strength of the Quadriceps

muscle was assessed using the Q Force at 110 degrees knee extension utilizing 4

repetitions on two occasions with a three to eight day interval between occasions.

Muscle strength was expressed in Newton meters (Nm) means (SD). T-tests were

performed to determine differences between measurement days. Reliability was

analyzed by calculating the ICCs and LOA.

Reliability was excellent since ICC coefficients were higher than 0.75. The LOA for

the peak torque for the left side were -18.6 Nm to 33.8 Nm and for the right side

-9.2 Nm to 26.4 Nm. Small systematic and significant differences in means were

ascertained between measurement occasions. It is concluded that the Q Force has

an excellent test-retest reliability, however, the LOA are substantial. Since the Q

Summary

141

Force is relatively inexpensive and mobile, it is suitable for application in various

clinical settings, however, its capability to detect changes in muscle force over time

is limited but similar to existing instruments.

Current protocols used to determine strength generally apply 1 to 3 measurements

on a single measurement day. It is not clear how precise these protocols estimate

maximum muscle strength. The objectives as described in Chapter 5 were to analyze

the outcomes for older adults of repeated Quadriceps strength measurements by

using a handheld dynamometer. In total, 44 older adults, 14 male and 30 female,

participated. Mean (SD) age was 76.8 (7.4) years, mean (SD) bodyweight was 79.5

(12.8) kg, and body height was 167.3 (6.1) cm. Measurements were performed

using a MicroFet 2 hand-held dynamometer on four separate days with a 2-day

interval. The break method was used employing three consecutive repetitions

of the left and right Quadriceps muscles with a 1-minute break in between each

repetition. Muscle strength expressed in Newton, means (SD). A linear mixed-

effects model regression analysis was performed.

Analysis of the results revealed no significant effects for repetitions within days

or between days. The standard errors were similar between the left and right

sides, ranging from 3 to 13 Newton. It is concluded that a single measurement is

sufficient to quantify muscle strength groups for older adults.

It has been demonstrated that strength can be reliably measured for adults

and children in various settings. However, a feasible and reliable instrument

to measure strength in persons with severe intellectual and visual disabilities

(SIVD) is lacking. The objectives as described in Chapter 6 were to first determine

feasibility of strength measurements; second, to analyze the learning period;

thirdly, to determine reliability of three methods of muscle strength testing; and,

fourthly, to analyze concurrent validity. In total, 29 participants with SIVD were

included and performed the Minimum Sit-to-Stand Height Test (MSST), the Leg

Extension Test (LET), and the 30 seconds Chair-Stand Test (30sCST) once per

week for 5 weeks. Feasibility was determined by the percentage of successful

measurements; the learning period was analyzed using a paired T test between

two consecutive measurements; test-retest reliability was analyzed using the ICCs

and LOA; and concurrent validity was analyzed using Pearson correlations. Results

showed sufficient feasibility for all test methods. The learning period ranged from

Summary

142

no learning period for the LET to 4 weeks for the MSST. Test-retest reliability was

sufficient. Correlations between test methods was moderate to sufficient. It was

concluded that the MSST, the LET, and the 30sCST are feasible tests for measuring

muscle strength in persons with SIVD and have sufficient test retest reliability.

The main findings of this thesis, the relevance of strength measurements, and

the relevance for clinical practice are discussed in the general discussion (Chapter

7). The strengths and weaknesses of the studies are examined, and directions

for further research are provided. The primary conclusions of this thesis are that

muscle strength appears to be time and region specific and should be regularly

and regionally updated; the Q Force possesses comparable reliability and LOA

compared to existing instruments; repeated measurements do not lead to a more

precise estimate of muscle strength in older adults; and strength measurements

are feasible and reliable in individuals with severe intellectual and visual

impairment within an acceptable learning period.

Summary

143

Samenvatting

144

Samenvatting Spierkracht is belangrijk voor alle menselijke fysieke activiteiten, in het dagelijkse

leven, sport en hobby. Om vast te stellen of spierkracht van iemand normaal of

verlaagd is dient de gemeten kracht worden vergeleken met referentiewaarden.

Voor een juiste vergelijking behoren deze referentiewaarden te zijn verkregen uit

een groep mensen met vergelijkbare eigenschappen als de onderzochte persoon.

Het is niet zeker of de referentiewaarden die momenteel in Nederland gebruikt

worden wel bruikbaar zijn voor de klinische praktijk. Ook is het niet duidelijk of

referentiewaarden van 20 jaar geleden nog actueel en bruikbaar zijn voor de

klinische praktijk in Nederland.

Een veel gebruikte methode om spierkracht te meten is hand-dynamometrie.

Met een hand-dynamometer, een klein en daardoor mobiel apparaatje met een

krachtsensor er in, wordt de geleverde spierkracht geregistreerd.

Figuur 1, Een handdynamometer

Hand-dynamometrie is een betrouwbare methode om spierkracht binnen een

groep mensen te bepalen. Dat wil zeggen dat de uitkomsten van herhaalde

metingen dicht bij elkaar liggen. De mate van betrouwbaarheid op groepsniveau

wordt uitgedrukt in een intraclass correlatiecoëfficiënt (ICC), waarbij 0 betekent dat

er geen betrouwbaarheid is en 1 betekent een maximale betrouwbaarheid (geen

variatie in resultaten bij herhaalde metingen). Hand-dynamometrie toegepast

om spierkracht te meten binnen 1 persoon is minder betrouwbaar omdat de

variatie in meetresultaten aanzienlijk is. Meetvariatie wordt uitgedrukt in de “

limits of agreement” (LOA). Voor spierkracht bepalingen op individueel niveau is

Samenvatting

145

er een behoefte aan meetinstrumenten die mobiel zijn en tevens een kleine intra

individuele variatie met zich mee brengen. Wanneer spierkracht worden gemeten,

door bijvoorbeeld een fysiotherapeut, dan bestaat het gebruikte protocol in de

meeste gevallen uit drie herhalingen die achtereen worden uitgevoerd, met 1

minuut pauze tussen de herhalingen. Het is echter niet duidelijk of dit protocol tot

een betrouwbare schatting leidt.

Over het algemeen kan spierkracht op groepsniveau betrouwbaar worden gemeten

bij gezonde individuen en bij individuen met aandoeningen in verschillende

settingen. Het is echter niet bekend of spierkracht betrouwbaar gemeten kan

worden bij personen die minder goed instrueerbaar zijn bijvoorbeeld met ernstige

intellectuele en visuele beperkingen.

In hoofdstuk 1 worden de onderzoeksthema’s van dit proefschrift geïntroduceerd

en worden de doelstellingen beschreven.

Zoals hierboven al beschreven zijn de referentiewaarden die in Nederland worden

gebruikt, enerzijds 20 jaar oud of gebaseerd op een populatie uit de VS. Het is

niet duidelijk of deze waarden nog steeds kunnen worden gebruikt in de klinische

praktijk of dat het mogelijk is de referentie waarden uit de VS te bruikbaar zijn

voor de Nederlandse populatie. De doelstellingen van de studie zoals beschreven

in hoofdstuk 2 waren, ten eerste; referentiewaarden voor werkende volwassenen

in Nederland bepalen, ten tweede; onderzoeken of de referentiewaarden uit

de VS overeenkomen met de huidige Nederlandse populatie, ten derde; de

betrouwbaarheid van krachtmetingen met behulp van hand-dynamometrie in de

onderzoekspopulatie te herbevestigen.

In totaal werden 462 gezonde werkende volwassenen onderzocht (259 mannen,

203 vrouwen). De spierkracht van de grote arm en beenspieren werd onderzocht

met een handdynamometer. De spierkracht werd uitgedrukt in Newton (N) met

3 herhalingen op 1 dag. De uitkomsten van de metingen van onze studie werden

vergeleken met die uit studies uit de VS. Daarnaast werd met behulp van ICC en

LOA geanalyseerd wat de betrouwbaarheid van en de variatie in meetresultaten

was

Op basis van de verrichte metingen zijn de referentiewaarden voor Nederlands

vastgesteld. Vergelijking van spierkrachtgegevens van onze studie met die van

Samenvatting

146

de VS bracht belangrijke verschillen aan het licht. Mannen in de studie uit de VS

waren over het algemeen sterker dan de mannen uit Nederland terwijl vrouwen

uit die studie VS over het algemeen minder sterk waren dan de vrouwen uit onze

studie. De betrouwbaarheid van de metingen was met ICC’s tussen 0,83 en 0,95

uitstekend. De intra-individuele variatie van de meetresultaten van varieerde

tussen 32 N (schouder abductie) en 117 N (knie extensie), hetgeen overeen komt

met 18 tot 31% van de gemeten kracht. Geconcludeerd werd dat spierkracht

regionaal/ nationaal bepaald is, referentiewaarden uit verschillende landen niet

onderling uitwisselbaar zijn en dat betrouwbaarheid van spierkrachtmetingen

goed is, maar de variatie binnen een persoon aanzienlijk is.

De referentiewaarden die in Nederland gebruikt worden om spierkracht van

kinderen mee te vergelijken zijn nu 20 jaar oud. Het is niet bekend of deze waarden

nu nog gebruikt kunnen worden in de klinische praktijk ook is niet bekend of de

nationale verschillen, gevonden bij volwassenen, ook aanwezig zijn bij kinderen.

De doelstellingen van de studie zoals beschreven hoofdstuk 3 waren ten eerste;

referentiewaarden voor spierkracht voor kinderen in Nederland bepalen,

ten tweede; de gevonden waarden vergelijken met eerder gerapporteerde

Nederlandse - en recent gerapporteerd Chileense referentiereferentiewaarden,

ten derde; de spierkracht statistisch te voorspellen op basis van leeftijd, lengte,

gewicht en geslacht.

In totaal werd de spierkracht van de grote arm en beenspieren van 1.252 kinderen,

594 meisjes en 658 jongens, variërend van 8 tot 18 jaar met behulp van de hand-

dynamometer onderzocht. De spierkracht werd gemeten met drie herhalingen op

1 dag en de spierkracht werd uitgedrukt in Newton.

Uit de analyses bleek dat de spierkracht van kinderen uit de huidige studie in 29

van 72 vergelijkingen statistisch significant lager was dan die uit de studie van 20

jaar geleden. Dit verschil op tot 187 N voor knie extensie voor jongens van 16 jaar.

In vergelijking met een Chileense studie uit 2016 bleken de Nederlandse kinderen

systematisch sterker in alle leeftijdsgroepen voor alle gemeten spiergroepen. De

verschillen liepen op tot meer dan 30% van de gemeten waarde bij jongens van

15 jaar. De betrouwbaarheid van de metingen was met ICC’s tussen 0,80 en 0,95

ook hier uitstekend, maar ook hier bleek de intra individuele variatie aanzienlijk,

variërend 44 N (elleboog extensie rechts) tot 101 N (knie extensie rechts) wat

Samenvatting

147

overeen komt met 21 tot 36% van de gemeten waarden (LOA). De variantie van de

metingen kon voor 46 tot 66 % verklaard worden door leeftijd, lengte, gewicht en

geslacht. Door deze studie kwamen referentiewaarden en regressievergelijkingen

beschikbaar voor Nederlandse kinderen. Spierkracht bleek niet alleen verschillend

tussen landen, maar ook binnen landen in de tijd aan verandering onderhevig

en dat spierkracht slechts te dele is te voorspellen op basis van leeftijd, lengte,

gewicht en geslacht.

In de zoektocht naar mobiele en betrouwbare meet instrumenten om spierkracht

te bepalen werd de Q Force ontwikkeld.

Figuur 2, De Q force

De doelstelling van de studie zoals beschreven in hoofdstuk 4 was het bepalen

van de test-hertest betrouwbaarheid van isometrische Quadriceps spierkracht

metingen met de Q Force bij ouderen. In totaal werd de spierkracht van 41 gezonde

ouderen, 13 mannen en 28, vrouwen gemeten, met een leeftijd van gemiddeld 81,9

± 4,9 jaar. Het meetprotocol was 4 herhalingen op 2 verschillende meetdagen met

3 tot 8 dagen tussen de meetdagen. Spierkracht werd gemeten in Newtonmeters

en eventuele verschillen tussen uitkomsten op de meetdagen werden statistisch

getoetst. De betrouwbaarheid was goed bij gevonden ICC’s groter dan 0,75. De

intra-individuele betrouwbaarheid was ook hier groot en varieerde van 25 tot 40%

van de gemeten spierkracht. Er werden tevens kleine, systematische verschillen

(in de orde van grootte van 10%) gevonden tussen de meetdagen. Er werd

geconcludeerd dat de Q Force een goede test-hertest betrouwbaarheid heeft,

Samenvatting

148

maar dat ook hier weer de intra-individuele variatie aanzienlijk was. Omdat de

Q Force relatief goedkoop is lijkt deze geschikt voor toepassing in verschillende

klinische omgevingen. Het vermogen om veranderingen in spierkracht binnen een

individu in de loop van de tijd te detecteren is beperkt, maar dit is vergelijkbaar

met andere bestaande meetinstrumenten.

Zoals reeds beschreven bestaan protocollen die in de klinische praktijk gebruikt

worden om spierkracht te meten meestal uit 3 herhalingen op 1 meetdag. Het

is echter niet duidelijk hoe nauwkeurig deze protocollen zijn om de maximale

spierkracht te bepalen. Meetprotocollen met meer herhalingen zouden tot hogere

meetresultaten kunnen leiden door leereffecten, maar ook tot lagere resultaten

door vermoeidheid. De doelstelling zoals beschreven in hoofdstuk 5 was het

analyseren van de resultaten van herhaalde Quadriceps krachtmetingen bij

ouderen met behulp van een handheld dynamometer.

In totaal werden 44 ouderen, 14 mannen en 30 vrouwen onderzocht met

eengemiddelde (sd)leeftijd van 76,8 (7,4) jaar. De Quadricepskracht werd

onderzocht met 3 opeenvolgende herhalingen, op 4 afzonderlijke dagen met

een interval van 2 dagen. In de statistisch analyse werd een regressieanalyse

verricht. Daarnaast werd geanalyseerd of er een binnen meetdag effecten en of

een tussen meetdag effecten waren. Er bleken geen significante verschillen te zijn

binnen of tussen meetdagen. De standaard meetfouten waren links en rechts

vergelijkbaar en varieerden van 3 tot 13 N. Er werd geconcludeerd dat een enkele

meting voldoende is om spierkracht van de Quadriceps van oudere volwassenen

te bepalen op groepsniveau.

Kracht kan, zoals uit het bovenstaande al blijkt, betrouwbaar worden gemeten

bij volwassenen en kinderen in verschillende settingen. Spierkracht is ook

betrouwbaar te meten bij patiëntengroepen met diverse (chronische) pathologiën.

Het is echter niet duidelijk of spierkracht metingen haalbaar zijn en of deze

betrouwbaar zijn bij mensen met een ernstige intellectuele of visuele beperking

(EIVB). De doelstellingen zoals beschreven in hoofdstuk 6 waren, ten eerste; om

de haalbaarheid van krachtmetingen te bepalen bij mensen met EIVB, ten tweede;

de leerperiode hiervan te analyseren, ten derde; de betrouwbaarheid van drie

methoden voor spierkrachttesten te bepalen en ten vierde; te vergelijken in

hoeverre de testen dezelfde theoretische eigenschap meten.

Samenvatting

149

In totaal werden 29 mensen met EIVB onderzocht. De volgende testen werden

uitgevoerd; de Minimale Zit-tot-Sta Hoogte test (MSST), de Leg Extension test

(LET) en de 30 seconden Chair-Stand Test (30sCST). De testen werden 1 keer per

week gedurende 5 weken uitgevoerd. De haalbaarheid werd bepaald door het

percentage succesvolle metingen te registreren. De leerperiode werd geanalyseerd

door de uitkomsten van twee opeenvolgende weken met elkaar te vergelijken. De

test-hertest betrouwbaarheid werd geanalyseerd met behulp van ICC en LOA. De

associaties tussen de testen werd geanalyseerd met behulp van Pearson correlaties

(aantoonbare verbanden). De leerbaarheid periode van de testen varieerde van

geen (LET) tot 4 weken (MSST). De test-hertest betrouwbaarheid, was goed: ICC’s

varieerden van 0,96 tot 0,99. De intra individuele variatie (LOA) was met 17% van

de gemeten waardes aanzienlijk. De associaties tussen de testmethoden waren

laag. Geconcludeerd werd, dat de MSST, de LET en de 30sCST haalbare tests zijn

voor het meten van spierkracht bij personen met de EIVB, met voldoende test-

hertest betrouwbaarheid, maar de testen meten ieder wat anders.

De belangrijkste bevindingen van dit proefschrift, de relevantie van

krachtmetingen voor de klinische praktijk, worden besproken in de algemene

discussie (Hoofdstuk7). Daarnaast worden de sterke en zwakke punten van

de studies besproken en suggesties voor verder onderzoek worden gegeven.

De belangrijkste conclusies van dit proefschrift zijn: spierkracht is tijden land

specifiek en moet regelmatig, regionaal worden bijgewerkt; de betrouwbaarheid

van de Q Force is vergelijkbaar aan die van andere instrumenten; herhaalde

metingen leiden niet tot een nauwkeurigere meting van spierkracht bij oudere

volwassenen; en krachtmetingen zijn haalbaar en betrouwbaar bij personen met

ernstige intellectuele en visuele beperking binnen een aanvaardbare leerperiode

Dankwoord

Dankwoord

152

DankwoordHet laatste woord.. Graag wil ik iedereen bedanken, die op wat voor manier dan

ook, betrokken is geweest bij het tot stand komen van dit proefschrift, alsmede

iedereen die me heeft bijgestaan in het voltooien van dit proefschrift. Zonder

iemand tekort te willen doen, zou ik graag een aantal mensen in het bijzonder

willen bedanken.

Allereerst wil ik mijn begeleiders bedanken, mijn 1e promotor Prof. dr. C.P. van der

Schans, mijn 2e promotor Prof. Dr. P.U Dijkstra en copromotor Dr. W.P. Krijnen;

Kees, Prof. Dr. C.P. van der Schans, mijn 1e promotor. Ik ben erg blij dat je bij mijn

promotie aanwezig kunt zijn, na een wel even moeilijke als bijzondere periode.

We gaan al lang terug: het AZG, UMCG, de ALA en ERS congressen, jouw zeilboot

Serendipity, de “moedige mannentocht” op de Noordzee met motorpech, terwijl de

wind wegviel en natuurlijk de mannenweekenden. Dank voor je professionaliteit

om de afgelopen jaren werk en privé te scheiden. Het heeft al met al wel wat

langer geduurd dan we aanvankelijk dachten. Ik herinner me nog op de dijk op

Schiermonnikoog ,ergens in 2012, dat je zei: ”Rob, misschien moet jij ook maar

gaan promoveren.” Je hebt je in de afgelopen jaren vast nog wel eens achter je oren

gekrabd vanwege die woorden. Dank voor je ideeën en inzichten met betrekking

tot de relevantie van het onderwerp van mijn proefschrift, je accurate feedback,

heldere inzichten, humor en ook geduld, ook in tijden dat ik privé het één en ander

te verwerken had. Zonder jou als mijn promotor en initiator was mijn promotie

niet mogelijk geweest. Het bleek uiteindelijk een grote uitdaging voor me. Een

metafoor voor mijn promotietraject wat ik samen met je heb afgelegd doet me

denken aan het liedje van the Beatles: a long and winding road.

Wim, Dr. W.P Krijnen, mijn copromotor, zonder jou was mijn promotie niet

mogelijk geweest. Vanaf het eerste begin was je bij hierbij betrokken. Jou

inzichten, feedback en strenge statistische blik zijn bijzonder waardevol geweest.

Je hebt me in- en rondgeleid in de wereld van de statistiek. Regelmatig heb je me

op het goede spoor gezet als ik van het pad was geraakt. Je commentaar in de

manuscripten was fantastisch prikkelend, zoet en impliciet en waar nodig expliciet

en ongezouten. Het zette me altijd aan het denken. Ik ben je dankbaar voor de

creatieve en accurate statistische oplossingen, alsmede de wijze waarop je mij de

afgelopen jaren begeleid hebt.

Dankwoord

153

Pieter, Prof. Dr. P.U. Dijkstra, mijn tweede promotor. Het is toch wel bijzonder,

twee promotores te hebben die ik al zo lang ken uit de AZG, UMCG tijd. Ook

wij delen passie voor zeilen en hebben hier menig gesprek over gehad. Onze

samenwerking en daarmee jou bijdrage had een zorgelijke oorzaak. Je hebt in

het laatste deel van dit traject weer wind in mijn zeilen geblazen waardoor de

boot weer vaart gegeven werd. Vanwege onverwachte, ontwikkelingen heb ik nu 2

promotores. Dank je wel, dat je de begeleiding over wilde nemen, toen dat nodig

was en dank voor de manier waarop je dit gedaan hebt.

Naast de begeleiders wil ik ook mijn mede auteurs bedanken. Annemarie

Dijkhuizen, je bent mijn maatje: persoonlijk, als docent en als auteur. Ik ben

er trots op dat ik in een artikel van jou als tweede auteur sta. Wat hebben we

nagedacht, geworsteld, gelachen en veel van elkaar geleerd. Ook de pijn in mijn

rug herinner ik me nog bij aanvang van de eerste studie in jou promotie periode.

Dank voor alles.

Geranda Slager, wat een organisatorisch talent heb je. Wat jij heb geregeld voor het

meten van spierkracht bij schoolkinderen, scholen en het meten van spierkracht

bij ouderen, is heel bijzonder. Ook jouw inbreng is van bijzonder belang geweest

in 3 van de manuscripten van mijn promotie traject.

Remko Soer: dank voor alle metingen die je hebt verricht en voor je feedback

ten behoeve van de referentiewaarden voor spierkracht bij volwassen. Zonder jou

was dit manuscript niet tot stand gekomen.

Michiel Reneman: ook jij bedankt voor je waardevolle bijdrage en het spiegelen in

het manuscript met betrekking tot het ontwikkelen voor referentiewaarden voor

spierkracht bij volwassenen.

Wybren Zijlstra en Ruben Regterschot: dank voor het feit dat ik kon aanschuiven

in een deel van een ZonMw project: de Q Force, bij Bewegingswetenschappen van

de Rijksuniversiteit Groningen. Dank voor jullie waardevolle feedback en bijdrage

aan het manuscript van de Q Force.

Geen enkel manuscript was mogelijk zonder bijdrage van alle mensen die zich

hebben willen laten meten. Zonder jullie zou er geen letter op papier staan en zou

er niets van de grond zijn gekomen. Leerlingen van basisschool het Karrepad, de

Borgmanschool, de Haydnschool, van het Winklerprins College en het Maartens

Dankwoord

154

College. Ook de moedige ouderen van de verzorgingstehuizen als de Ebbingepoort

en de Heymanstichting: hartelijk dank voor jullie moeite, moed en inspanningen.

Dank ook aan leidinggevenden van de scholen en instituten die ons de gelegenheid

hebben gegeven om de metingen te verrichten.

Hartelijk dank studenten, en ook collegae Fysiotherapie van de Hanzehogeschool

Groningen: Zonder jullie zou er geen Newton op de hand-dynamometer staan.

Met hele meutes zijn we naar de verschillende scholen gegaan. Met soms wel 30

of 40 mensen tegelijk. Wat een organisatie was het en wat een avontuur. Dank

voor alle inspanningen. Samen waren jullie goed voor bijna 50.000 spierkracht

metingen. Een vlotte rekensom leert dat jullie ongeveer 12.500.00 Newton aan

spierkracht hebben tegengehouden tijdens alle metingen.

Hartelijk dank ook Jan Peter Landsman, teamleider Fysiotherapie, voor je steeds

positieve inbreng tijdens het hele project. En ja, de rust komt. Dank iedereen van

de app groep “E……”; Ron, Paul, Marie, Egbert, Harrie, Tim, Roland. Dank voor

ruggensteun, feedback, relativering, flauwe grappen, klappen, inhoudelijk- en

zinloze discussies.

Hartelijk dank, Willem de Kok, voor het rotsvaste vertrouwen en de altijd positieve

feedback.

Hartelijk dank Bernarda Mulder voor je juiste woorden op het juiste moment.

Beatrijs……… terugkijkend op het vele werk, plezier, ontwikkeling en de lange

adem: het allerbelangrijkste is de liefde binnen ons gezin en met jou, met een

glas wijn, zitten aan het eind van de steiger. Rob-Jan, door er te zijn, heb je alles

voor mij deze jaren in perspectief gezet; wat een kerel ben je. Lizelot en Lucija;

ook jullie hebben bijgedragen aan het besef dat liefde binnen het gezin het

allerbelangrijkste is.

Dankwoord

155

Research Institute SHARE


158

Research Institute SHAREThis thesis is published within the Research Institute SHARE (Science in Healthy

Ageing and healthcaRE) of the University Medical Center Groningen / University

of Groningen.

Further information regarding the institute and its research can be obtained from

our internet site: http://www.share.umcg.nl/

More recent theses can be found in the list below.(supervisors are between brackets)

2021

Akbari F Chronic pain in the context of the lives of dyads; cognitions, behaviors, and well-

being

(prof M Hagedoorn, prof R Sanderman, dr M Dehghani)

Hepping AMGrip on recovery after paediatric forearm fractures

(prof SK Bulstra, prof JHB Geertzen, dr M Stevens)

Beijers LParsing the heterogeneity of major depression

(prof RA Schoevers, dr KJ Wardenaar, dr HM van Loo)

Köhler TC Providing color to the pharmacy technician; a new profession within the pharmacy

team

(prof ADC Jaarsma, dr M Westerman)


159

Bunk SFFrontal brain functioning and pain; possible underlying mechanisms of increased

pain responses in age- and dementia-related cognitive impairment

(prof SU Zuidema, dr M Kunz)

Bosáková LBreaking the cycle of poverty; routes to counteract intergenerational transmission

of socioeconomic health differences

(prof SA Reijneveld, prof A Madarasová-Gecková)

Vendeloo SN vanOptimizing learning environments and resident well-being in postgraduate

medical education

(prof PLP Brand, prof SK Bulstra, dr CCPM Verheyen)

Sampurna MTAImproving the management of hyperbilirubinemia in a limited-resource area

(prof AF Bos, dr CV Hulzebos, dr PH Dijk, dr R Etika)

Siswanto JERetinopathy of prematurity; how to prevent retinopathy of prematurity in preterm

infants in Indonesia?

(prof AF Bos, prof A Adisasmita, dr PH Dijk)

Kaper MSImproving communication in healthcare for patients with low health literacy;

building competencies of health professionals and shifting towards health literacy

friendly organizations

(prof SA Reijneveld, prof AF de Winter)


160

Schuurmans JPopulation-based expanded carrier screening reporting couple results only: a

mixed methods approach

(prof IM van Langen, prof AM Lucassen, prof AV Ranchor, dr M Plantinga)

Vrijsen JTowards dementia risk reduction among individuals with a parental family history

of dementia

(dr N Smidt, prof SEJA de Rooij)

Dams ACAchilles tendon rupture; current clinical practice, imaging and outcome

(prof RL Diercks, prof J Zwerver, dr I van den Akker-Scheek, dr I Reininga)

Buitenhuis AHIt takes two: the role of a non-smoking partner in a quit attempt; a look at dyadic

planning and daily interactions

(prof M Hagedoorn, dr MA Tuinman)

Minh AMental health, education and work in Canada, the Netherlands, and the United

States; a comparative, life course investigation

(prof U Bültmann, dr CB McLeod, prof SA Reijneveld, dr M Guhn)

Marcus-Varwijk AEPerspectives on health and health promotion in community-dwelling older people;

a mixed-methods study

(prof JPJ Slaets, prof AV Ranchor, dr CHM Smits, dr TLS Visscher)


161

Bochane MIUniform screening for atypical language development in Dutch child health care

(prof CP van der Schans, prof SA Reijneveld, dr MR Luinge)

For earlier theses visit our website

Clinical Muscle Strength Measurements: Reference Values And Reliability

Rob Douma - Hanze

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