The purpose of this study was to investigate the characteristics of baseball pitching motion in young pitchers. Sixty-five asymptomatic pitchers were analyzed with a motion capture system. The subjects were classified into two groups according to their age: A: 34cases (10-15 years old), B: 3lcases (19-34 years old). Kinematic and kinetic parameters were used to compare the differences between the two groups. Abduction and horizontal adduction angles of the upper arm were smaller in group A at ball release. The trunk was less flexed and twisted, but was bent much more toward the non-throwing side in the group A. There were no significant differences between the two groups with regard to the elbow angles, the wrist angles and the interval from arm-cocking phase to ball release. Our results showed that the young pitchers tend to put their pitch arm behind their trunk at ball release. That position is not close to “Zero Position”. It causes stretching the anterior structure of the shoulder. Furthermore, the shoulder is overloaded by the rotational stress from the end of armcocking phase to ball release. Repetition of this stress might cause epiphyseal damage for young pitchers. The young pitchers should be taught proper pitching mechanics. Limitation on pitches might be able to reduce the risk of epiphyseal damage in young pitchers.
