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

比较了不同水平的棒球内野手出手动作的运动学和运动学差异。被试分别来自小学(E组，n=22)、初中(J组，n=18)、高中(H组，n=20)和大学生(C组，n=16)。通过使用两个高速摄像机的三维DLT技术分析每个人的投放动作。E组内野手上躯干和骨盆后倾较小，上躯干和骨盆前倾较大，肩关节外旋和外展较大，肩水平外展较少，关节动力学产生较少。J组内野手上躯干和骨盆向左倾斜较大，肘关节伸展较大，关节动力学产生较少。H组内野手上躯干和骨盆向右倾斜较大，肩关节水平内收，肘关节屈曲，骨盆后倾。C组内野手站立更直立，骨盆后倾角较小，肘关节屈曲较大，肩关节内外旋和肘关节屈伸活动范围较大，产生较大的肩关节和肘关节动力。这些结果表明，每个级别都可以采用特定的投掷技术来提高投掷的效率，这将使内野手在提高表现的同时减少过度使用受伤的风险。这些结果为理解投掷成绩的可能提高和预防过度使用伤害提供了一个从一个层次到下一个层次的基础。

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.