COORDINATION OF MONOARTICULAR AND BIARTICULAR MUSCLES IN MULTI-DEGREE-OF-FREEDOM ELBOW MOVEMENTS

We investigated the coordination of mono- and bi-articular muscles dur ing movements involving one or more degrees of freedom at the elbow. S ubjects performed elbow flexion (or extension) alone, forearm pronatio n (or supination) alone, and combinations of the two. In bi-articular muscles such as biceps brachii and pronator teres, the amplitude of ag onist electromyographic (EMG) activity was dependent on motion in the two degrees of freedom. Agonist burst amplitudes for combined movement s were approximately the sum of the agonist burst amplitudes for movem ents in the individual degrees of freedom. Activity levels in individu al degrees of freedom were, in turn, greater than activity levels obse rved when a muscle acted as agonist in one degree of freedom and antag onist in the other. Other muscles such as triceps, brachialis, and pro nator quadratus acted primarily during motion in a single degree of fr eedom. The relative magnitude and the timing of activity between sets of muscles also changed with motion in a second degree of freedom. The se patterns are comparable with those reported previously in isometric studies.