Analysis of Range of Motion and Isokinetic Strength of Internal and External Rotation According to Humeral Retroversion of the Dominant Shoulder in Youth Baseball Players: A Pilot Study

BACKGROUND: We aimed to analyze the range of motion (ROM) and internal rotation (IR) and external rotation (ER) isokinetic strength according to humeral retroversion of the dominant shoulder. METHODS: We included 40 elite baseball players in Korea (OBP group: n=20 players with careers spanning >10 years, age: 19.37±2.21 years, height: 181.00±5.41 cm, weight: 84.58±7.85 kg; BBP group: n=20 players with careers spanning <10 years, age: 16.55±1.36 years, height: 177.27±7.57 cm, weight: 77.27±8.14 kg). Radiography was performed to examine humeral retroversion, a goniometer was used to measure IROM and EROM, and a dynamometer was used to measure IR and ER isokinetic strength (speed set at 180°/s or 300°/s). RESULTS: The BBP and OBP groups had significantly different IR and ER isokinetic strength (180°/s and 300°/s) (P<0.001) and dominant shoulder retroversion (P=0.009). In the BBP group, retroversion had no correlation with ROM and with IR or ER isokinetic strength (180°/s and 300°/s). In the OBP group, retroversion had no correlation with ROM and with ER isokinetic strength at 180°/s, but had significant correlation with IR isokinetic strength at both 180°/s (r=0.483, P=0.007) and 300°/s (r=0.373, P=0.043) and ER isokinetic strength at 300°/s (r=0.366, P=0.046). CONCLUSION: Thus, youth players with careers spanning >10 years had significantly higher humeral retroversion, IROM, EROM, and IR and ER isokinetic strength of the dominant shoulder than youth players with careers spanning <10 years. Furthermore, humeral retroversion and ROM were not significantly related, but IR and ER isokinetic strength were significantly positively related with retroversion in both groups.