Meeting Abstract

43.2  Saturday, Jan. 5  Functional significance of plantigrade foot posture in humans: implications to the evolution of foot posture in great apes CUNNINGHAM, CB*; CARRIER, DR; University of Utah; University of Utah c.cunningham@utah.edu

Plantigrade foot posture, in which the heel contacts the substrate during a step, is a derived character of great apes. We used human subjects to test two hypothesizes: 1) greater torques can be applied to the ground with plantigrade than with digitigrade foot posture, and 2) the cost of transport (COT) is lower during walking and running with plantigrade than with digitigrade foot posture. Ten subjects performed maximum effort lateral pushes and 90 degree cutting turns on a Kistler force plate while maintaining either foot posture. The average maximum torque generated during lateral pushes from a plantigrade stance was approximately 2-fold greater than digitigrade posture. The difference during cutting turns was more dramatic; plantigrade maximum torques were approximately 5-fold greater. Hence, plantigrade foot posture does appear to provide a performance advantage in the production of ground torques. We also measured the COT during walking and running at slow and moderate speeds with plantigrade versus digitigrade foot posture. The COT during running did not differ when the subjects used plantigrade versus digitigrade foot posture. Walking with digitigrade foot posture, however, does appear to be significantly more expensive than walking with plantigrade posture. Because the application of ground torques is essential to sharp turning performance and physical aggression, we suggest that plantigrade foot posture may have evolved in apes to enhance fighting performance associated with male-male competition. The retention of this posture in the terrestrial Hominina (e.g., Australopithecus and Homo) may also be associated with male-male competition, but also likely confers an energetic advantage during walking.