Three-Dimensional Interactions in a Two-Segment Kinetic Chain. Part II: Application to the Throwing Arm in Baseball Pitching

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Abstract
Fastball pitches of eight collegiate baseball pitchers were filmed using the Direct Linear Transformation (DLT) method of three-dimensional (3D) cinematography. Coordinate data were obtained, and the model developed by Feltner and Dapena (1989) was used to fractionate the 3D angular acceleration of the upper arm and distal segment (the forearm, the hand, and prior to release, the baseball) of the throwing arm into terms associated with the joint torques exerted on the segments and the kinematic variables used to define the motions of the segments. The findings indicated that the extreme external rotation of the upper arm during the pitch was due mainly to the sequential actions of the horizontal adduction and abduction muscles at the shoulder. The study also found that the rapid elbow extension prior to ball release was due primarily to the counterclockwise angular velocity of the upper arm and trunk (viewed from above) that occurred during the pitch, and not to the elbow extensor muscles.

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