A Modified Approach to Define Walking Center of Mass Mechanical Energy Recovery: Human Walking Involves Energy Loss Throughout Stance

An exchange between potential and kinetic energy over the step has long been considered a key feature in the energetic effectiveness of human walking. However, it is difficult to identify mechanisms responsible for limiting such an exchange in human walking. This study proposes a modified definition of center-of-mass (COM) energy recovery (Rc) that quantifies the proportion of mechanical energy transferred from one step to the next while accounting for total step dissipation. Simulations show that Rc decreases nearly linearly with walking speed on level ground, indicating no preferred speed. This behavior arises from analytical formulations that neglect active work during single support (pendular motion). In contrast, empirical data reveal consistently lower Rc, likely due to elevated collision losses or negative net single-support work not captured by the analytical model. When both single- and double-support phases are considered analytically, Rc exhibits a maximum of 59.4% at 1.21 m.s-1, coinciding with minimal active muscle work over the step. We further show that the Rc trajectory is asymmetric, contrary to prior assumptions, and is governed by total step dissipation. Accordingly, challenging walking conditions associated with higher metabolic cost, such as restricted visual lookahead, are predicted to reduce Rc (maximum 58.5%).