Body size, body shape, and long bone strength in modern humans

To identify behaviorally significant differences in bone structure it is fi rst necessary to control for the effects of body size and body shape. Here the scaling of cross-sectional geometric properties of long bone diaphyses with different "size" measures (bone length, body mass, and the product of bone length and body mass) are compared in two modern human populations wit h very different body proportions: Pecos Pueblo Amerindians and East Africa ns. All five major long bones (excluding the fibula) were examined. Mechani cal predictions are that cortical area (axial strength) should scale with b ody mass, while section modulus (bending/torsional strength) should scale w ith the product of body mass and moment arm length. These predictions are b orne out for section moduli, when moment arm length is taken to be proporti onal to bone length, except in the proximal femoral diaphysis, where moment arm length is proportional to mediolateral body breadth (as would be expec ted given the predominance of M-L bending loads in this region). Mechanical scaling of long bone bending/torsional strength is similar in the upper an d lower limbs despite the fact that the upper limb is not weight-bearing. R esults for cortical area are more variable, possibly due to a less direct d ependence on mechanical factors. Use of unadjusted bone length alone as a " size" measure produces misleading results when body shape varies significan tly, as is the case between many modern and fossil hominid samples. In such cases a correction factor for body shape should be incorporated into any " size" standardization. (C) 2000 Academic Press.