Leg and joint stiffness in human hopping

The present study investigated the regulation of leg and joint stiffness in hopping at different intensity levels. Eight male subjects performed bilateral hopping at various intensity levels that were determined by peak vertical ground reaction force (GRF). In addition to the GRF, the measurements included hopping kinematics and electromyography (EMG) of selected leg muscles. While the leg and ankle joint stiffness remained invariant, the knee joint stiffness increased significantly (P<0.01) with the hopping intensity. EMG analysis revealed a significant increase in averaged EMG for all the measured muscles before and during the early phase of ground contact (P<0.05-0.001) with increasing h…