Department of Human Evolutionary Biology, Harvard University
Friday 8:45-9:00, Grand Ballroom II
The assumption that biacetabular breadth (BAB) relative to leg length affects the cost of bipedal locomotion has led to the inference that Australopithecus and Homo differed in how efficiently they walked. Although previous work has examined the relationship between pelvic width and mechanical advantage of the lesser gluteal muscles using static mechanical models, few studies have experimentally tested the effects of BAB and muscle mechanical advantage on metabolic cost of different gaits. We collected data on oxygen consumption during bipedal walking and running in a mixed-sex sample of fit human subjects. Kinematic data were also collected using reflective markers placed on relevant pelvic and femoral landmarks and a three-dimensional infrared motion capture system. BAB was estimated from the known relationship among pelvic bony landmarks, and scaled by hindlimb length. Lesser gluteal mechanical advantage was calculated from interlandmark distances. Multiple regressions indicated no significant relationship between muscle mechanical advantage and cost of transport during both walking and running. Furthermore, at both slow and fast walking speeds, the relationship between relative BAB and metabolic cost was weak (R2 ≤ 0.16). However, during running, there was a strong positive linear relationship between relative BAB and metabolic cost of transport (R2 = 0.69). These results suggest that relatively widely spaced acetabulae was not a major cost for Australopithecus and that decreased biacetabular breadth in the genus Homo improved running economy. BAB, however, is only one of many measures of pelvic width, and we discuss its relationship to other aspects of hip and pelvic width.
This work was supported by funding from the American School of Prehistoric Research and the Hintze Family Charitable Foundation.