Changes in humeral torsion and shoulder rotation range of motion in high school baseball players over a 1-year period

BackgroundThe torsional stress on a baseball player's throwing limb has been theorized to affect humeral retrotosion during skeletal maturity. This study investigated 1) changes in humeral retrotorsion and shoulder rotation range of motion over a 1-year period in high school baseball players, and 2) relationship between a 1-year change in dominant limb retrotorsion and the number of seasons participants played on organized baseball teams.MethodsHumeral retrotorsion and shoulder range of motion were measured a year apart in a total of 138 high school baseball players. Baseball participation history over the year was captured using a questionnaire. Changes in bilateral humeral retrotorsion and range of motion over a year and effects of baseball participation on changes in humeral retrotorsion and range of motion were assessed using analysis of variance models.FindingsHumeral retrotorsion did not significantly change over the year regardless of the number of seasons participants played baseball (P > 0.05). The participants' dominant limb internal rotation range of motion decreased slightly over a year (2.0°, P = 0.015), while external rotation (7.8°, P < 0.01) and total rotation (11.9°, P < 0.01) range of motion decreased bilaterally among the participants who only played baseball in 1 season.InterpretationAdaptation in humeral retrotorsion seems to occur prior to high school age. Our observations suggest that change in shoulder range of motion in high school baseball players are attributed to soft tissue contracture. This provides a support that stretching exercises should be implemented when significant changes in range of motion are identified in high school baseball players.