Differential activation of the biceps brachii heads in normal subjects

To facilitate the use of upper limb myoelectric prostheses, we investigated if and how muscle compartments, i.e intra-muscular subdivisions each innervated by a nerve branch, could be voluntarily contracted. Five pairs of electrodes were positioned across the short head of the biceps brachii and 5 others across its long head. Electromyographic signals from 4 able subjects were collected. They produced voluntary isometric and isotonic contractions with the arm kept in different positions while the hand was either fully supinated, neutral or fully pronated. Root mean square value of the signals, from the 5 electrode pairs across the long and short heads were averaged. Depending on the task, activity was found larger in one head or in the other. Being able to activate either head of the biceps, while not yet completely independently, suggests that the selective use of compartments could be a possible avenue for controlling myoelectric prostheses.