JOINT-DEPENDENT MECHANISMS TO ADAPT TO AN IMBALANCE BETWEEN FLEXION AND EXTENSION FORCES IN HUMAN GAIT

In human gait, alternating leg flexion/extension movements essentially require the production of extension muscle forces due to the large co ntribution of passive forces to leg flexion. In this experiment, we st udied the adaptive capabilities of walking subjects constrained with e lastic cords which further facilitated leg flexion and impeded leg ext ension. In order to walk, the subjects let the moments created by the elastic cords increase the ankle flexion during the whole cycle, which allowed them to reduce part of these moments. By contrast, at the kne e level, they increased their extension muscle activity to compensate for the remaining constraint moments during the swing phase, which res ulted in unchanged kinematics. Although neuromuscular locomotor synerg y is often considered to control the lower limb as a unit, we showed h ere that different adaptive mechanisms can act at different joints of the same leg.