EMG biofeedback as a tool for simulating the effects of specific leg muscle weakness on a lifting task

This study investigated the we of EMG biofeedback to simulate weakened rect us femorii and gastrocnemii muscles during the performance of a lifting tas k. Eight healthy women performed 15 kg free-style lifts from floor level. T hree conditions were tested: unconstrained lifting, lifting with rectus fem orii activity volitionally limited bilaterally through EMG biofeedback to l ess than 45% of maximal EMG activity, and lifting with the gastrocnemii lim ited to a similar level. Limiting leg muscle activity through biofeedback l ed to an alteration of lifting strategy, with resulting performance variabl es (joint angles and torques, angular velocities, center of pressure excurs ion, and segment coordination) comparing favorably with those from lifting trials performed by six women with moderate leg muscle weaknesses. The data indicate that EMG biofeedback can be used to simulate the effects of leg m uscle weakness during these lifts, providing a new tool to study the biomec hanics of muscle weakness.