An EMG analysis of the shoulder in throwing and pitching. A preliminary report.

Five male subjects' throwing and pitching motions were analyzed by dynamic electromyography and high speed photography. Electrodes inserted into the deltoid and rotator cuff muscles attempted to define muscle activation patterns during the throwing and pitching cycle. The wind-up or preparation (Stage I) had no consistent pattern. Cocking (Stage II) had a sequential muscle activation pattern of first deltoid activity, followed by the S.I.T. muscles and finally by the subscapularis muscle. Acceleration (Stage III) had a lack of muscle activity, even though the arm was accelerating forward in space. Follow-through (Stage IV) was the most active stage with all the muscles firing intensely. The muscle patterns observed during the cycle were largely characteristic of attempts to decelerate the arm.