ORIGINAL PAPER/SPECIAL ISSUE Relationship between humeral torsion angle and shoulder range of motion among juvenile baseball players

Summary Background The humeral torsion angle (HTA) of throwing athletes is known to be greater on the throwing side than on the non-throwing side. However, little information is available regarding detailed changes in HTA and actual shoulder range of motion during the growth period. Materials and Methods Subjects comprised 357 male baseball players from elementary school to senior high school (age range, 9-17 years). Age, height, weight, and years of experience playing baseball were elicited as background factors. External rotation in abduction (ABER) and internal rotation in abduction (ABIR) were measured, and HTA was assessed with the support of ultrasonography. Results HTA decreased with age on the non-throwing side, but remained unchanged on the throwing side. The difference between sides thus increased with age. A lateral difference in ABER was found in players >11 years old, and a lateral difference in ABIR was found in all players. The lateral difference in HTA was correlated with increased age, greater height and weight, and longer experience playing baseball. Conclusions The repetitive load of throwing motions restricts the normal processes acting to decrease HTA and affects shoulder range of motion during the growth period.