Reassessing the role of foot power in human gait

The foot acts as the primary interface to the ground during bipedal locomotion. It absorbs and returns energy over stance as the longitudinal arch deforms and recoils. The term arch recoil evokes the concept that the foots returned energy directly propels the centre of mass forward by lifting the talus. However, recent work has shown that arch recoil does not directly drive the body forward; instead, it lowers and posteriorly tilts the talus, putting it into a more favourable position for upright gait. Here, we aim to supply a kinetic explanation for this mechanism. We applied the unified deformable power approach to highly accurate talus kinematics from biplanar videoradiography and force plate measurements to measure the power absorbed/produced by the foot. We coupled these measurements with a simple mathematical model that allowed us to restrict rotation and linear actuation of the talus caused by the recoil of the arch to demonstrate that positive foot power primarily contributes to posteriorly tilting the talus. This suggests the role of positive foot power during propulsion is to keep the talocrural surface in a more favourable position for upright gait rather than directly propelling the centre of mass forwards. These findings highlight that arch mobility during push-off is critical for allowing the ankle to directly propel the body forward and upward during the propulsive phase of gait.