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.