The influence of velocity and force on motor unit firing behaviour during dynamic contractions of the biceps brachii

We investigated the effect of movement speed and load on motor unit firing behaviour during repeated flexion/extension contractions of the Biceps Brachii. At all speeds and loads, greater motor unit firing rates were observed during the concentric vs. eccentric phases of the movement. However, different speeds and loads of the contraction were associated with changes in firing rates, rate of increase of firing rates, and recruitment angles, shedding light on the control mechanisms used by the nervous system to regulate dynamic activities.