SHOULDER AND ELBOW MUSCLE-ACTIVITY IN GOAL-DIRECTED ARM MOVEMENTS

This research examined the electromyographic (EMG) activity of shoulde r and elbow muscles during reaching movements of the upper limb. Subje cts performed goal-directed arm movements in the horizontal plane. Mov ements which varied in amplitude, speed, and direction were performed in different sections of the workspace. EMG activity was recorded from the pectoralis major, posterior deltoid, biceps brachii short head, b rachioradialis, triceps brachii long head, and triceps brachii lateral head; motion recordings were obtained with an optoelectric system. Th e analysis focused on the magnitude and timing of opposing muscle grou ps at the shoulder and elbow joints. For hand movements within any giv en direction of the workspace direction, kinematic manipulations chang ed agonist and antagonist EMG magnitude and intermuscle timing in a ma nner consistent with previous single-joint findings. To produce reachi ng movements in different directions and areas of the workspace, shoul der and elbow agonist EMG magnitude increased for those hand motions w hich required higher angular velocities, while the timing between oppo sing muscle groups at each joint was invariant.