The aim of this study was to investigate the differences of range of motion of the shoulder between elementary school and high school baseball players. We studied 35 elementary school baseball players(group ES) and 46high school baseball players(group HS). Internal rotation and external rotation of the shoulder with the arm abducted 90°(2nd IR and ER), internal rotation with the arm flexed 90°(3rdIR), horizontal flexion(HF), gleno humeral abduction (Abd) were measured bilaterally. The measurements were compared between the dominant and nondominant shoulders. The differences between the dominant and nondominant shoulders were compared between group ES and group HS. In group ES,2nd IR,2nd total rotation,3rd IR, and HF were statistically less and 2nd ER was statistically greater in the dominant shoulders than in the nondominant shoulders. There was no statistical difference in Abd. In group HS,2nd IR,2nd total rotation,3rd IR, HF, and Abd were statistically less and 2nd ER was statistically greater in the dominant shoulders than in group ES. The differences between the dominant and nondominant shoulders in the 2nd IR,2nd total rotation,3rd IR, and HF were statistically greater in group HS than in group ES. It seems that the 2nd IR decrease in the dominant shoulders in group HS was caused by not only retroversion of the humeral head, but also severer posterior shoulder tightness than in group ES. A change in the 2nd IR& ER range of motion of the nondominant shoulder from elementary school to high school baseball players may reflect the decrease of retroversion of the humeral head with growth.
