Effects of repetitive baseball throwing on hip muscle strength and trunk and pelvic motions at the shoulder's maximum external rotation position during the late cocking phase and ball release.

[Purpose] This study aimed to investigate the changes in the trunk and pelvic lateral tilt angles at the shoulder's maximum external rotation during the late cocking phase (MER) and ball release (BR) and hip muscle strength during repetitive throwing. [Participants and Methods] In this study, 12 male baseball players participated. During the throwing, which was filmed using a high-speed video camera, the trunk and pelvic lateral tilt angles toward the nonthrowing side were measured at the MER and BR. Hip muscle strength during abduction, adduction, and external internal rotations were measured on the throwing and nonthrowing sides. Repetitive throwing was performed for nine innings, with 15 pitches per inning. Throwing motion was compared during innings 1, 7, 8, and 9. Hip muscle strength was measured before and after repetitive throwing. [Results] Compared with the trunk lateral tilt angle toward the nonthrowing side at BR in inning 1, the angle in innings 8 and 9 increased. The strength of hip abduction, adduction, and external and internal rotations on the throwing and nonthrowing sides decreased after repetitive throwing. [Conclusion] Hip muscle strength decreases after 135 pitches, and throwing >120 pitches changes the trunk lateral tilt angle at BR.