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

Abstract

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.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).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).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.