Meeting Abstract

87.5  Wednesday, Jan. 7  Plantigrade foot posture increases locomotor economy in walking but not in running humans. CUNNINGHAM, C; SCHILLING, N; ANDERS, C; CARRIER, D*; Univ. of Utah, Salt Lake City; Friedrich-Schiller-Univ. Jena; Univ. Hospital Jena; Univ. of Utah, Salt Lake City carrier@biology.utah.edu

Plantigrade foot posture, in which the heel (calcaneus) contacts the substrate during a step, is a derived character of great apes (Hominidae). We used human subjects (N=11) to test the hypothesis that the energetic cost of transport (COT, oxygen consumed to travel a given distance) is lower during walking and running with plantigrade than with digitigrade foot posture. When the subjects walked with their heels slightly elevated, COT increased by 63 + 8% (mean + SEM) above that of plantigrade walking. In contrast, at each of the four speeds we tested, there was no difference in COT when subjects ran with digitigrade versus plantigrade foot posture. Subsequent observations and experiments suggest that the greater economy of plantigrade walking results from a suite of factors. First, stride length decreased when the subjects walked with digitigrade posture, resulting in higher stride frequencies (9.0 + 1.0%) and accounting for a 15% increase in metabolism in a control experiment. Second, electromyography indicates that recruitment of the main extensor muscles of the ankle, knee, hip, and back is higher during walking with digitigrade foot posture. Third, preliminary analysis of the mechanical work done on the center of mass suggests (1) that the positive external work is approximately 11% greater during digitigrade walking, and (2) the potential to save energy via a transfer of gravitational potential and forward kinetic energy is reduced during digitigrade walking. Relative to other species, humans are exceptionally economical walkers, but not economical runners. The structure and posture of the human foot may help explain how humans are able to walk economically.