Meeting Abstract
Functional differences among joints may help to coordinate overall leg function during locomotion. Legs have been hypothesized to exhibit a proximal-distal gradient in joint mechanical function: from power production at the hip to spring-like behavior at the ankle. However, potentially distinct joint functions must sum together to result in the overall spring-like function of legs during running and strut-like function of legs during walking. We tested the hypothesis that individual leg joints exhibit functional differences during both walking and running. We developed quantitative indices that characterize joint energy management based on mechanical analogs: strut, motor, spring, and damper. The strut index is the dimensionless ratio between the power and moment. The motor, spring and damper indices characterize the nature of mechanical joint work: energy production, absorption followed by production, and absorption, respectively. Consistent with our hypothesis, in humans the hip acts as a motor, the knee as a damper, and the ankle as a spring during running. During walking, knee function becomes more complex, but the hip remains motor-like and the ankle remains spring-like. Leg joint function was consistent with a proximal-distal gradient. Understanding the contribution of differential joint function to overall leg and body mechanics is an important neuromechanical question with potential implications for understanding morphology, scaling, and evolution. Moreover, the indices we developed could be useful for quantitatively understanding function in many contexts, including for muscles and other tissues.
