Motor unit diversity during elbow flexion

Understanding how multiple muscles are recruited across a joint has typically been approached from relating muscle activity to resultant forces. New tools are now available to look deeper into a muscle's recruitment by observing groups of single motor units. Identifying changes in the motor unit activity both within a muscle and between muscles the redundancies in motor control can be better understood. Motor units from biceps brachii and brachioradialis were decomposed from surface electromyography to determine firing rate and timing behaviors. Biceps peak firing rates, recruitment time and time to reach peak firing rate had positive correlation with increases in resultant force, while brachioradialis data had no such correlation. In addition the brachioradialis firing rate distribution was significantly different from the biceps. The stark differences in firing behavior show differences in function for both muscles, with the biceps acting more as a primary force producer, and the brachioradialis acting as a force modulator.