INTRODUCTION Shoulder pain is the most common complaint in swimming. Muscle stiffness in the posterior shoulder is associated with shoulder pain in overhead sports(Myers et al., 2006). However, this relationship is unclear in swimmers. This muscle stiffness can be measured as the shear elastic modulus using ultrasonic shear wave elastography (SWE). The purpose of this study was to investigate and identify risk factors for shoulder pain in swimmers based on elastic muscle coefficient by SWE, joint range of motion, and isometric muscle strength. METHODS Forty-eight competitive swimmers (18-28 years; 29 males) were followed up for 6 months. Baseline measurements of the elastic modulus of the pectoralis minor, supraspinatus, infraspinatus, posterior deltoid, and pectoralis minor muscles were obtained using shear wave elastography. Range of motion and isometric strength were measured using a goniometer and a handheld dynamometer, respectively. The questionnaire was administered weekly to determine shoulder pain occurrence over 6 months. Additionally, differences between shoulders with and without pain were investigated using the Mann-Whitney U test. Logistic regression analysis and recipient operating characteristic curves identified the risk factors. RESULTS Forty-six swimmers (96%) were followed up for 6 months, and 20 reported shoulder pain. Predictors in the final model included muscle stiffness of the posterior deltoid. The predictor, muscle stiffness of the pectoralis minor, was extracted only for females. DISCUSSION High posterior deltoid stiffness was associated with and predictive of shoulder pain development in swimmers. Pectoralis minor muscle stiffness was a risk factor for shoulder pain in female swimmers. Maintaining the posterior deltoid and pectoralis minor muscle flexibility in conditioning was suggested.
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