The shoulder is injured alone more often with the serve than with other strokes. Unlike pitching which involves throwing down, serving requires the ball to go up and arc over the net. During windup, the arm is positioned by the body with little shoulder muscle activity required. In the cocking phase, glenohumeral stability is provided by a sharp increase in rotator cuff and biceps activity supported by the scapular positioning function of the serratus anterior, which by far demonstrates the highest level of activity. The acceleration phase is characterized by a peak in internal rotator muscle activity from the subscapularis, pectoralis major, and latissimus dorsi, while the serratus anterior continues to maintain proper scapular positioning.
Muscular activity is highest in the acceleration phase.
With the forehand the highest activity is found with the subscapularis, biceps, pectoralis major, and the serratus anterior. With the backhand, the peak contributors were the middle deltoid, supraspinatus, and the infraspinatus. Some activity is also noted for the biceps, latissimus dorsi, and serratus anterior. The follow-through for the forehand is characterized by high activity of the serratus anterior, subscapularis, infraspinatus, and biceps. For the backhand, follow-through is characterized by moderate activity of the biceps, middle deltoid, supraspinatus, and infraspinatus.