A BIOMECHANICAL STUDY OF THE DEVELOPMENTAL ASPECTS REGARDING THE DELIVERY MOTION AMONG VARIOUS LEVELS OF BASEBALL INFILEDER

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Kinematic and kinetic differences of the delivery motion among various level of the baseball infielders were compared. A total of 76 infielders from the elementary school (group E, n=22), junior high school (group J, n=18), high school (group H, n=20), and collegiate (group C, n=16) were participated in the present study. The delivery motions for each individual were analyzed by a three-dimensional DLT technique using two high-speed video cameras. Group E infielders had less upper trunk and pelvis backward tilt, greater upper trunk and pelvis forward tilt, greater shoulder external rotation and abduction, less shoulder horizontal abduction, and less joint kinetics productions. Group J infielders had greater upper trunk and pelvis leftward tilts, greater elbow extension, and less joint kinetics productions. Group H infielders had greater upper trunk and pelvis rightward tilts, shoulder horizontal adduction, elbow flexion, and pelvis backward orientation. Group C infielders stood more erect, and had less pelvis backward orientation, greater elbow flexion, greater ranges of motion for the shoulder external-internal rotation and elbow flexion-extension, and generated greater shoulder and elbow joint kinetics. These results suggest that a specific throwing technique used each level could be adopted to increase the efficiency of the delivery throw, which would allow a infielder to improve performance with decreased risk of overuse injury. These results provide a basis for understanding the possible improvement of throwing performance and prevention of overuse injury from one level to the next.