Are Adult Physiques Geometrically Similar? The Dangers of Allometric Scaling Using Body Mass Power Laws Alan M. Nevill, 1 Arthur D. Stewart, 2 * Tim Olds, 3 and Roger Holder 4 1 School of Sport, Performing Arts and Leisure, University of Wolverhampton, Walsall, WS1 3BD UK 2 Department of Biomedical Sciences, University of Aberdeen, Aberdeen, Scotland, AB25 22D UK 3 School of Physical Education, Exercise and Sports Studies, University of South Australia, Underdale, South Australia, 5032 Australia 4 School of Mathematics and Statistics, University of Birmingham, Birmingham, B15 2TT UK KEY WORDS corrected girth; anthropometry; allometric scaling; athlete ABSTRACT Human physique classification by soma- totype assumes that adult humans are geometric similar to each other. However, this assumption has yet to be adequately tested in athletic and nonexercising human populations. In this study, we assessed this assumption by comparing the mass exponents associated with girth mea- surements taken at 13 different sites throughout the body in 478 subjects (279 athletic subjects, and 199 nonexercis- ing controls). Corrected girths which account for subcuta- neous adipose tissue at the upper arm, thigh, and calf sites, and which simulate muscle circumference, were also calculated. If subjects are geometrically similar to each other, girth exponents should be approximately propor- tional to M 1/3 , where M is the subjects’ body mass. This study confirms that human adult physiques are not geo- metrically similar to each other. In both athletic subjects and nonexercising controls, body circumferences/limb girths develop at a greater rate than that anticipated by geometric similarity in fleshy sites containing both muscle and fat (upper arms and legs), and less than anticipated in bony sites (head, wrists, and ankles). Interestingly, head girths appear to remain almost constant, irrespective of subjects’ body size/mass. The results also suggest that thigh muscle girths of athletes and controls increase at a greater rate than that predicted by geometric similarity, proportional to body mass (M 0.439 and M 0.377 , respectively). These systematic deviations from geometric similarity have serious implications for the allometric scaling of vari- ables such as energy expenditure, oxygen uptake, anaer- obic power, and thermodynamic or anthropometric studies involving individuals of differing size. Am J Phys An- thropol 124:177–182, 2004. © 2004 Wiley-Liss, Inc. In 1921, the first systematic anthropometric as- sessment of humans was proposed as a rationale for testing human efficiency by quantifying body tissues in a sample of barbers, butchers, blacksmiths, and gymnastics instructors (Matiegka, 1921). The au- thor recognized that “above average stature is not always an indication of physical superiority.” In the decades which followed, other physique descriptions referred to as “somatotyping” were proposed (Shel- don et al., 1940; Parnell, 1954), and these were later revised by Heath and Carter (1967). The latter com- prised the primary physique assessment tool still in use today, based on 10 anthropometric measure- ments. These generate the coordinates for a tripolar schema involving fatness, musculoskeletal robust- ness, and mass in relation to stature. The authors stated that the resulting somatotype “is a measure of shape, not size,” with the inherent assumption that adults of differing size are geometrically simi- lar. Subsequent decades were witness to a rapid increase in the prevalence and severity of obesity, and to unprecedented muscle gains due to more sophisticated training or pharmacological interven- tion. As such, humanity exhibits an “expanding uni- verse” of possible physiques, in which the bound- aries are being continually pushed back. This has enabled an increased variance in physique which, with sufficient data, can test the hypothesis of whether geometric similarity is observed in humans. A useful insight into the issue is provided by com- parison of different animal species. Larger mam- mals expend more energy than smaller mammals due to their larger energy cost of metabolism and locomotion. However, if energy expenditure is ex- pressed as a simple ratio standard, per unit body mass, smaller mammals consume more energy per unit body mass than larger mammals. A theoretical *Correspondence to: Arthur D. Stewart, Ph.D., Department of Bio- medical Sciences, University of Aberdeen, Aberdeen, AB25 22D UK. E-mail: a.d.stewart@abdn.ac.uk Received 21 February 2003; accepted 22 April 2003. DOI 10.1002/ajpa.10351 Published online 19 September 2003 in Wiley InterScience (www. interscience.wiley.com). AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 124:177–182 (2004) © 2004 WILEY-LISS, INC.