Motor unit mechanisms of balance in the quadriceps muscle

We investigated changes in quadriceps motor unit firing behaviour during 2-leg vs. 1-leg squat exercises. In both tasks, motor unit firing rates of the Vastus Lateralis (VL) muscle were significantly lower during eccentric vs. concentric phases of the squat. However, as the subjects moved from 2-leg to 1- leg squats, motor units manifested relatively greater increases in firing rates during eccentric movement resulting in no significant difference in firing rates between eccentric and concentric phases. These findings may indicate that greater activation is needed during 1-leg squats to accommodate increased demand of load, balance and stability.