Post on 28-Apr-2023
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.
REFERENCES
Ames, K. (2002). Digital asset management, Part 1. Photoshop User, 5, 44-45.
Blade, L. (1993). Growth of adipose tissue volume and maturity in children. Unpublished
Doctoral dissertation, Simon Fraser University, Burnaby, BC.
Carter, J. E. L., & Heath, B. H. (1990). Somatotyping – development and applications.
Cambridge: Cambridge University Press.
Crawford, S. (1990). Morphometric Models for the Assessment of Developmental Status of
Boys age 7 to 16. Unpublished Doctoral dissertation, Simon Fraser University,
Burnaby, BC.
Hopkins, W. G. (2000). Reliability from consecutive pairs of trials (Excel spreadsheet).
Retrieved March 3rd, 2003, from sportsci.org/resource/stats/xrely.xls
Hopkins, W. G., Schabort, E. J., & Hawley, J. A. (2001). Reliability of power in physical
performance tests. Sports Medicine, 31(3), 211-234.
Norton, K., Olds, T., Olive, S., & Craig, N. (1996). Anthropometrica. Marrackville: UNSW
Press.