Elbow and shoulder kinetics for 26 highly skilled, healthy adult pitchers were calculated using high-speed motion analysis. Two critical instants were 1) shortly before the arm reached maximum external rotation, when 67 N-m of shoulder internal rotation torque and 64 N-m of elbow varus torque were generated, and 2) shortly after ball release, when 1090 N of shoulder compressive force was produced. Inability to generate sufficient elbow varus torque may result in medial tension, lateral compression, or posteromedial impingement injury. At the glenohumeral joint, compressive force, joint laxity, and 380 N of anterior force during arm cocking can lead to anterior glenoid labral tear. Rapid internal rotation in combination with these forces can produce a grinding injury factor on the labrum. After ball release, 400 N of posterior force, 1090 N of compressive force, and 97 N-m of horizontal abduction torque are generated at the shoulder; contribution of rotator cuff muscles in generating these loads may result in cuff tensile failure. Horizontal adduction, internal rotation, and superior translation of the abducted humerus may cause subacromial impingement. Tension in the biceps tendon, due to muscle contraction for both elbow flexion torque and shoulder compressive force, may tear the anterosuperior labrum.

The American Sports Medicine Insfitute conducts research to increase understanding of mechanisms involved in upper extremity injuries to throwing athletes. This paper presents a qualitative overview of pitching and a detailed quantitative description of arm motion about the shoulder during this highly dynamic activity. Data on kinematics of arm motions about the shoulder are presented for 29 elite throwers. The major motion about the shoulder is externallinternal rotation. Scapulothoracic and glenohumeral flexibility permit the arm to reach an externally rotated position of 175". Approximately 30 msec before release, the arm internally rotates 8O0, reaching peak angular velocities near 7,00O0/sec. In rehabilitation of injured throwers, there is a need to appreciate the Charles J. Dillman Glenn S. Fleisig highly dynamic nature of this skill and to attempt to simulate these dynamic motions and loads as part of the final phase of treatment before the athlete returns to competition.

A r m motion in throwing is extremelv violent. Perhaps n o throw is m o r e dvnamic than baseball pitching, and, as ;i result. there is a high incidence o f elbow in.juries in pitchers (3,7,(10)(11)(12). If better preventive a n d rehabilitative programs a r e t o b e developed, it is important t o understand t h e biomechanics of t h e pitching motion. T h e purpose o f this studv is t o quantify t h e joint kinematics (ie.. ranges o f motion a n d joint velocities), joint kinetics (ie.. joint forces a n d torques), a n d muscle activitv about t h e elbow a n d explain t h e relevance o f these results for injury prevention a n d rehabilitation. Previous studies have reported either joint kinetics (4. 6) or muscle activitv (3, 8 , 10). but this study represents t h e first effort t o simultaneously quantifv a n d correlate both. METHODS Testing ProcedureSeven healthy college a n d minor league pitchers were tested in a n ind o o r biomechanics laboratory. T h e pitchers had a n average height o f 1.8 m a n d a n average mass of 89.7 kg. F~c h athlete pitched from a n in-

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