Biomechanical adaptations of the shoulder in collegiate swimmers

Shonk, Kelsey E.
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University of Delaware
Context: Several studies have found alterations in range of motion, posterior shoulder tightness, posterior capsular thickness, and humeral retrotorsion among overhead throwing athletes. However, despite its popularity and high incidence of shoulder pain, few studies have been conducted on swimmers to determine whether similar adaptations occur. Objective: The purpose of this study was to determine if biomechanical adaptations develop in swimmers' shoulders and how those changes are related to injury history and distance specialty. Methods: 26 swimmers volunteered (8 males, 18 females; 5 distance, 21 sprint swimmers; 6 injured, 20 uninjured swimmers) to take part in this study. A post-test only study design was used to analyze glenohumeral internal and external rotation, scapular upward rotation, and posterior shoulder tightness (humeral horizontal adduction) by an inclinometer. Posterior capsular thickness and humeral retrotorsion (HR) were examined through diagnostic ultrasound. All measurements were performed on both the dominant and non-dominant arms. Prior to testing all subjects completed a questionnaire to asses injury and swimming history. Results: A 3 way ANOVA was run for each dependent variable. The dominant arm was found to have greater external rotation (p=0.002), but less internal rotation (p=0.001), upward rotation at 90° (p=0.039), and upward rotation at 120° (p=0.046) than the non-dominant arm. Uninjured swimmers and sprinters had significantly greater HR than their injured (p=0.008) and distance (p=0.017) counterparts. There was a significant correlation between HR and IR on both the dominant (r=-.461, p=0.014) and non-dominant (r=-.428, p=0.023) sides. All other variables were not significant. Conclusions: The dominant arms of swimmers display some anatomical and biomechanical adaptations, but less than other overhead athletes. The development of humeral retrotorsion in swimmers is reflected in both distance specialty and injury susceptibility. Soft tissue characteristics, such as posterior capsule thickness, offer less insight of shoulder injury and specialty in a swimming population.