Title: Digital photogrammetry versus ISAK anthropometry in determining body segment

lengths of powerlifters.

Running title: Digital photogrammetric method for body segment lengths of powerlifters.

Authors: Peter Mellow, Patria A. Hume, Justin Keogh, Simon Pearson

Institutional affiliations:

Sport Performance Research Centre, Division of Sport and Recreation, Faculty of Health,

Auckland University of Technology, New Zealand

Acknowledgments: AUT funded this study. Thanks are given to the New Zealand

Powerlifting Association and the Australian Powerlifting Association for their support of the

project, the organisers of the Oceania Powerlifting and New Zealand Bench Press

competitions for access to the powerlifters and performance scores, to the powerlifters

who participated in the study, and to the ten anthropometrists who helped with data

collection.

Category: Sport Anthropometry: Original research.

Date of submission to Journal of Sport Biomechanics: 19th May 2003

ABSTRACT

The validity and reliability of digital photogrammetry and International Society for the

Advancement of Kinanthropometry (ISAK) anthropometry in determining body segment

lengths were determined. Sixty-eight Australasian and Pacific powerlifters (54 males and

14 females) were measured for 42 anthropometric dimensions (using ISAK protocols) and

had six digital photos taken in the front and back, left sagittal, right medial leg, right sagittal

arm and right sagittal leg planes.

The mean intra-tester reliability for the seven sites, as assessed by the technical error of

measurement (TEM) was 0.31% for digital photogrammetry and 0.90% for the ISAK

method. Both of these mean TEM were within acceptable ISAK limits (1.0%). However,

the inter-tester TEM for digital photogrammetry (1.64%) was greater than the ISAK

acceptable error level of 1.5%. A mean difference of 3.8% existed between the limb

segments lengths measured with digital photogrammetry compared to the ISAK values.

Greater error was found in the upper limb compared to the lower limb segments.

Therefore, digital photogrammetry does not yet appear as valid as ISAK anthropometry in

determining body segment lengths. Several potential sources of error have been identified

and with future development may reduce the error to acceptable levels.

Key words: Anthropometry, digital photogrammetry, ISAK anthropometry, body segment

lengths.

INTRODUCTION

An athlete’s anthropometric dimensions, reflecting body shape, proportionality and

composition, are variables that play a role in determining the potential for success in a

chosen sport (Norton et al., 1996). Athlete’s anthropometric characteristics are usually

physically measured according to the guidelines of The International Society for the

Advancement of Kinanthropometry (ISAK), a society that implements worldwide standards

in anthropometry via an accreditation system. The visual photoscopic somatotype rating of

an athlete (see Figure 1) is often used in conjunction with anthropometry. Technical errors

of measurement (TEM)1 are established for each anthropometrist with the limits for

acceptable error reducing with the increasing accreditation level of the anthropometrist

(Level 1 being a newly accredited anthropometrist, with level 4 being a criterion or expert

anthropometrist). “This is an objective method of maintaining quality control of all persons

who are accredited” (Norton et al., 1996 p. 397).

1 Technical Error of Measurement (TEM) is the square root of the sum of the differences squared divided by

the number of pairs of scores doubled.

Figure 1: Traditional somatotype photos. The athlete is 77.5 kg and 158 cm with an

anthropometric somatotype of 3.1 - 9.5 - 0.1.

Knowing the expected normal variation between repeated anthropometric measures is

essential for monitoring performance and/or studying the effect of an intervention. To

conclude that an intervention has had a real effect on performance, the change due to the

intervention must be greater than what would normally be expected with repeated

measurements under the same conditions. Examination of repeated trials under the same

conditions provides the reliability or repeatability of the measurements. A reliable test is

one that has small changes in the mean, small within-individual variation (coefficient of

variation) and a high test-retest correlation between the repeated tests (Hopkins, 2000;

Hopkins et al., 2001).

Digital photogrammetry is a relatively new method for measuring limb segments that holds

some advantages when measuring athletes (Blade, 1993; Crawford, 1990). Taking photos

of the athlete with the bony landmarks marked with a pen, allows the anthropometrist to

measure specific body segment lengths using their computer. This method is less invasive

for the athlete and allows a greater number of athletes to be tested in a given time

compared to manually measuring the athletes.

With the recent advancement in digital imaging technology we now have access to photo

images that are as high quality as film. Thus, the present study aimed to determine the

validity and reliability of using digital photogrammetry to determine body segment lengths

compared to the traditional ISAK anthropometric method for 53 powerlifters.

METHODS

Sixty-eight Australasian and Pacific powerlifters (54 males and 14 females) were

measured for 42 anthropometric dimensions (using ISAK protocols). Fifty-three of the

powerlifters agreed to have digital photos taken of them in six planes during the Oceania

Powerlifting Championships and the New Zealand Bench Press Championships.

The Auckland University of Technology Ethics Committee approved this study. All athletes

received verbal and written information about the study and gave written informed consent

prior to anthropometric measurement and being photographed.

Double measures for each of the 42 anthropometric dimensions (triple measures for

skinfolds) were obtained on the right side of the body using the ISAK protocols (Norton et

al., 1996). Measures included eight skinfolds (using a Slimguide calliper with 10 g.mm-2

constant pressure; Creative Health Products, Michigan), 13 limb/body girths (Lufkin

606PM, Cooper Tools, Ohio), 11 limb/body lengths (Rosscraft Segmometer, British

Colombia), four breadths and widths (Rosscraft Anthropometer, British Colombia), height

(Mentone Stadiometer, Victoria) and body mass (Secca scales). All anthropometrists were

ISAK level 2 or 3 accredited.

Digital photos (see Figure 2) were taken in the front and back, left sagittal, right medial leg,

right sagittal arm and right sagittal leg planes using a turntable (Rosscraft, British

Colombia) to rotate the powerlifter. Three of the photos (frontal, back and left sagittal) are

the traditional photoscopic somatotype photos, using the standard somatotype pose. The

other three (right medial leg, right sagittal arm and right sagittal leg) were chosen as they

displayed pen marks on the bony landmarks that were used for the anthropometry.

Figure 2: Digital photogrammetric poses. A) Right sagittal arm; B) Right sagittal leg; C)

Right medial leg. Bony landmarks are marked and visible.

A Fuji FinePix4700 digital camera (Fuji Photo Film, Tokyo), with a resolution of 2400 by

1800 pixels, was mounted on a tripod to record the digital photos of the powerlifters. The

lens to subject distance was 4.5 metres, following guidelines for film somatotype

photographs (Carter & Heath, 1990). Photos were managed by digital asset management

(DAM) software (iPhoto, Apple Computer) and measured using Photoshop 6.0 (Adobe

Systems). The “measure tool” within the Photoshop application was used to measure the

250 mm calibration line drawn on the support box (see Figure 3) to indicate the calibration

correction factor. Using the zoom function in Photoshop, the images on the computer

screen were magnified to 200% of their usual size.

Figure 3: A screenshot of the digital measurement of the Tibale laterale to floor body

segment length using the measure tool in Photoshop. The 250 mm calibration scale is

seen on the support box.

The digital method used the seven standard ISAK body segment lengths (1: Acromiale-

radiale; 2: Radiale-stylion; 3: Midstylion-dactylion; 4: Trochanterion-tibiale laterale; 5:

Tibale laterale-floor; 6: Foot length and 7: Tibiale mediale-sphyrion tibiale) measured

according to the ISAK method. Digital limb segment length was determined by multiplying

the apparent size (number of pixels) of each segment by the calibration correction factor.

The digital measure for each segment length was then compared to the length obtained by

the ISAK method. Results are expressed as mean and standard deviation.

Reliability of the digital photogrammetry measures was determined by re-digitising the

segment lengths. Inter- and intra-tester reliability was established by three

anthropometrists, trained in digital anthropometry, after three repeated measures on 10

athletes chosen randomly from the full database of athletes. The TEM was calculated for

the digital photogrammetry and the ISAK measures. Paired two tailed t-tests were used to

determine if significant differences existed between the segment lengths obtained with

digital photogrammetry measures compared to the ISAK measures. The a-priori level of

statistical significance was set at p < 0.05.

RESULTS

Of the 53 athletes who had their photos taken, not all body segment landmarks were easily

identified from the digital photo. Where a landmark was not easily identifiable, the

researchers did not measure the segment limb with the digital photogrammetric method.

Thus, across the group of 53 powerlifters, 19-53 measures were taken of each segment

length.

As indicated by the TEM scores in Table 1, the digital photogrammetry method (0.31%)

had greater intra-tester reliability than the ISAK method (0.90%). While inter-tester

reliability was determined for digital photogrammetry (1.64%), the inter-tester reliability for

the ISAK method was not established with the same population due to time constraints

when measuring the powerlifters during competition. However, the accredited

anthropometrists have all recently been assessed and have an inter-tester TEM of less

than 1.5%, as required by the ISAK guidelines. Thus, the inter-tester reliability of digital

photogrammetry was above that of the accepted ISAK limit of 1.5%.

Table 1: Body segment lengths for 10 Australasian and Pacific powerlifters using the

digital and ISAK methods.

DISCUSSION

A level three certified anthropometrist would typically take 10 minutes to mark and

measure the seven sites. Measurement time for the athlete may be reduced by half using

the digital photogrammetry method. Thus, digital photogrammetry may be a useful

anthropometric measurement technique as it allows a greater number of athletes to be

tested in a given time compared to manually measuring the athletes. However, while

minimising the inconvenience to the athlete is important, it is also crucial that the data

obtained is reliable and valid.

The intra-TEM was less for the digital photogrammetry than the ISAK measurements,

indicating greater reliability for the digital method. However, the inter-TEM for the digital

method was greater than the maximum error of 1.5% accepted by ISAK. This may be due

to a number of factors including the novelty of the digital technique and the

anthropometrists limited experience in digital photogrammetry.

The significant mean percentage differences between the ISAK and digital measurements

indicate that the validity of the digital method needs to be improved. Parallax error may

have contributed to less accuracy in some of the digital measurements, especially in the

upper arm where some athletes may have abducted their arm slightly while holding the

pose. To reduce this error, it is recommended that the athlete maintain a standardised

pose, in which the arm is held in a vertical position. This pose would be a modification of

the traditional somatotype pose.

The calibration scale used for this study was 250 mm in length. In retrospect, a metre rule

should have been utilised to allow greater precision of measurement. This would reduce

the relative error in the initial measurement of the calibration rule, and hence all

subsequent measures of body segment lengths. In addition, it is imperative that the

calibration scale is placed in the plane of the segments so that perspective error can be

reduced.

Horizontal pen marks (lines) on the skin above the bony landmarks were used as the

reference points for both the digital photogrammetric and ISAK methods. However, it was

difficult to clearly identify all the marked bony landmarks from some photos, even when

using the zoom function in Photoshop. Part of this problem may be due to the contrast of

the pen on the skin. This may be solved by the use of different pen colours for different

skin tones. In addition, some modifications to the ISAK protocol for marking the athlete

need to be considered. Extrapolation of some landmarks, such as distal styloid to the

plantar aspect of the hand would assist the identification of the limb segment, potentially

leading to greater reliability and validity of the digital photogrammetry method. The

horizontal landmark applied in the ISAK landmarking procedure should also have a vertical

mark placed at the centre, so this cross mark can assist the digital anthropometrist locate

these points. Using such a cross mark in contrast to a line, digital anthropometrists should

be able to increase their reliability and validity of measurement.

The quality of the digital image may also contribute to the error. In the present study, the

camera used JPEG (Joint Photographic Export Group) compression algorithms when

storing the photo. JPEG uses a ‘lossy’ compression routine and some of the original

information in the photo was lost. In future exploration of this method, it is recommend that

a camera with more pixels (6 million) be used as these cameras have the option to use a

‘lossless’ format such as TIFF (Tagged-Image File Format) files for their digital images

(Ames, 2002). The TIFF file format in conjunction with the greater number of pixels may

produce an image of greater quality, thus allowing more accurate determination of limb

segment lengths using digital photogrammetry.

CONCLUSION

Digital photogrammetric anthropometry is not yet as accurate as the ISAK anthropometric

method, but it exhibits high intra-tester reliability. The potential for considerable time-

savings when measuring an athlete and the non-invasive nature of the digital method

make it an attractive alternative if validity could be established. We have identified some

areas of potential improvement in the method and believe that incorporation of these

recommendations will increase the validity and inter-tester reliability of digital

photogrammetric anthropometry. Further investigation of the use of digital

photogrammetric anthropometry is recommended.

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Crawford, S. (1990). Morphometric Models for the Assessment of Developmental Status of

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