Physically Variable Compliance in Running

This paper explores the role and utility of variable compliance in running behaviors. While it is well understood in the literature that leg compliance plays an important role in running locomotion, our conjecture is that mechanically adjustable leg compliance improves the efficiency and robustness of a running system. We claim that variable compliance can serve as an effective means for gait regulation, and can enable energy efficient locomotion over a wide range of terrains and speeds. We draw inspiration from a number of observations in biomechanics, and use qualitative arguments and a simulation of our variable compliance actuator to support the underlying ideas.