2020 Volume 9 Issue 4 Pages 187-193
[Purpose] The purpose of this study was to investigate the thicknesses of the rotator cuff muscles in baseball players using ultrasound images. [Subjects] Thirty male (60 arms) with at least 3 years of hardball baseball club experience in high school and at least 5 years of baseball club experience were recruited. [Method] Participants responded to a questionnaire and underwent rotator cuff muscle thickness (throwing side and non-throwing side) measures using ultrasound images. [Results] Comparison of rotator cuff muscle thicknesses on the throwing and non-throwing sides revealed that the infraspinatus muscle was significantly thinner on the throwing side and the subscapularis muscle was significantly thicker on the throwing side. Comparisons of patients with and without medical histories related to the throwing shoulder revealed that, in the no throwing shoulder-related medical history group, there were no significant differences in position history or muscle thickness. However, these individuals were significantly more likely to have played as fielders. In contrast, the group with throwing shoulder-related medical histories included significantly pitchers and catchers. Multiple regression analysis of muscle thickness as the dependent variable and height, weight, years of experience, position history, and throwing shoulder-related medical history as independent variables revealed that infraspinatus and teres minor muscle thicknesses were negatively correlated with years of experience. [Conclusion] In baseball players with 5 years of baseball club experience, the infraspinatus muscle was thinner, and the subscapularis muscle was thicker, on the throwing side. Participants with no throwing shoulder-related medical histories were significantly more likely to play as fielders, whereas those with throwing shoulder-related medical histories were more likely to play as pitchers or catchers. Our results suggested that years of experience affect infraspinatus and teres minor muscle thicknesses.