A comparative electromyographic analysis of the shoulder during pitching

Dynamic, fine-wire, intramuscular electromyography (EMG) was performed on 12 different shoulder muscles in 13 normal male subjects as they pitched a baseball. Seven were major league baseball pitchers and six were amateur pitchers. The act of pitching a fast ball was filmed at 450 frames per second with the EMG signals recorded synchronously. The subscapularis, supraspinatus, and infraspinatus muscles were tested in 13 subjects, the biceps brachii muscle was tested in 12, and other shoulder muscles were tested variously among the subjects. Two groups of muscles were identified. Group I muscles, the supraspinatus, infraspinatus, teres minor, deltoid, trapezius, and biceps brachii, served primarily to position the shoulder and elbow for the delivery of the pitch. These muscles were found to have greater activity during the early and late cooking stages, with less activity during acceleration. Group II muscles accelerated the arm and baseball forward in space. These muscles, the pectoralis major, serratus anterior, subscapularis, and latissimus dorsi, had stronger activity during the propulsive phase of the pitch. The professional pitchers were able to use the muscles about the shoulder in an efficient manner to achieve greater pitching velocities. The subscapularis and latissimus dorsi muscles of Group II had stronger activity among the professionals, whereas the supraspinatus, teres minor, and biceps brachii muscles of Group I had only minimal activity. The amateurs, on the other hand, continued to use all of the rotator cuff muscles and the biceps brachii muscle of Group I through the acceleration stage of the pitch.(ABSTRACT TRUNCATED AT 250 WORDS)