Biomechanics of baseball pitching

Fifteen professional major league pitchers were filmed with high speed cinematography. One hundred forty-seven pitches were analyzed using an electromagnetic digitizer and a microcomputer. Three phases of throwing were studied: cocking, acceleration, and follow-through. The cocking phase is the period of time between the initiation of the windup and the moment at which the shoulder is in maximum external rotation. This phase occurs in approximately 1500 ms, and the shoulder is brought into an extreme position of external rotation. The acceleration phase and the initial stages of the follow-through phase produce extraordinary demands on the shoulder and elbow. The acceleration phase begins with the throwing shoulder in the position of maximum external rotation and terminates with ball release. This phase occurs in approximately 50 ms, and peak angular velocities averaging 6,180 deg/sec for shoulder internal rotation and 4,595 deg/sec for elbow extension were measured. The follow-through phase begins at ball release and continues until the motion of throwing has ceased. This phase occurs in approximately 350 ms.