KINETICS OF BASEBALL PITCHING WITH IMPLICATIONS ABOUT INJURY MECHANISMS

Elbow and shoulder kinetics for 26 highly skilled, healthy adult pitch ers were calculated using high-speed motion analysis. Two critical ins tants 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 genera te 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 d uring arm cocking can lead to anterior glenoid labral tear. Rapid inte rnal rotation in combination with these forces can produce a grinding injury factor on the labrum. After ball release, 400 N of posterior fo rce, 1090 N of compressive force, and 97 N-m of horizontal abduction t orque are generated at the shoulder; contribution of rotator cuff musc les in generating these loads may result in cuff tensile failure. Hori zontal adduction, internal rotation, and superior translation of the a bducted humerus may cause subacromial impingement. Tension in the bice ps tendon, due to muscle contraction for both elbow flexion torque and shoulder compressive force, may tear the antero-superior labrum.