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.
Takuya Aso, Yoshinori Kagaya
PMID 38304150WHAT IT FOUND
After throwing 135 balls, hip muscle strength dropped on both sides.
Trunk tilt toward the non-throwing side increased significantly at ball release after 120 pitches, but not at the earlier maximum external rotation point. Pelvic tilt did not change.
Key findings
01Hip abduction, adduction, external rotation, and internal rotation strengths decreased significantly on both the throwing and non-throwing sides after repetitive throwing.
02The trunk lateral tilt angle at ball release increased significantly in the 8th and 9th innings compared to the 1st inning, while pelvic lateral tilt angles remained unchanged.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study included only 12 participants, all male and aged over 20, limiting generalizability to younger players or females. Throwing was performed barefoot from a set position at a short distance (3 m) in a lab, which differs from actual game conditions. Two-dimensional video analysis was used, which may lack the accuracy of 3D motion capture for complex trunk and pelvic movements. Shoulder motion was not analyzed, so the direct link between trunk changes and shoulder load could not be measured.
Declared interests
The study received no funding, and the authors reported no conflicts of interest.
The easy way to misread this
Do not assume that hip weakness directly caused the increased trunk tilt. The study shows both occurred after repetitive throwing, but it did not measure the mechanical link between them or confirm that hip fatigue was the sole driver of the trunk motion change.