The relationship between shoulder external rotation strength, horizontal abduction, and glenohumeral distance ratios...

[Purpose] This study aimed to examine the association among zero-position external rotation muscle strength, shoulder horizontal abduction angle, and humeral head alignment. We hypothesized that individuals who cannot exert zero-position external rotation strength may adopt a horizontal abduction position and have difficulty maintaining a centripetal position for humeral head alignment. [Participants and Methods] Eighteen professional baseball players were included in the study. A handheld dynamometer was used to measure zero-position external rotation muscle strength. The isometric shoulder zero-position external rotation muscle strength was measured, and the weight ratio of the average value of the three trials was calculated. The shoulder horizontal abduction angle and anterior and posterior glenohumeral distances were measured using magnetic resonance imaging in the abduction external rotation position. The glenohumeral distance ratios were also calculated. We investigated the relationship between zero-position external rotation strength and shoulder horizontal abduction angle, anterior and, posterior glenohumeral distances, and glenohumeral distance ratios. [Results] Zero-position external rotation strength, shoulder horizontal abduction angle, and glenohumeral distance ratio were significantly negatively correlated. [Conclusion] Athletes who cannot exert zero-position external rotation strength may have a large horizontal shoulder abduction and glenohumeral distance ratio on magnetic resonance imaging.