ELECTROMYOGRAPHY OF SHOULDER MUSCLES IN RELATION TO FORCE DIRECTION

In a static Force task the electromyographic level of 74 shoulder musc les including 3 rotator cuff muscles was related to force direction. S urface and wire electrodes were used. The force direction of maximal e lectromyography (principal action) was identified for every muscle. Th e principal action expresses the function of a muscle in a specific si tuation. The deltoid was active in a Force direction that could be und erstood from its anatomy. The trapezius and serratus were mainly invol ved in stabilizing the scapula in upward and outward force directions. Large multiarticular muscles such as the pectoralis and the latissimu s were active in downward and forward forces. The rotator cuff seems t o have a specific role in stabilizing the glenohumeral joint. These da ta can be compared with data of patients with shoulder disorders and w ith kinematic data of a shoulder model.