The purpose of this study was to determine if a distinctive characteristic exists in the pattern of movement (scapular elevation and upward rotation to reduce impingement) and associated muscular activities during arm elevation in subjects with shoulder impingement (SI) that is associated with the severity of the disease. Fourteen subjects (7 amateur athletes and 7 student athletes) with SI and 7 controls performed arm elevation in the scapular plane. Scapular kinematics (upward rotation, elevation, tipping, and scapulohumeral rhythm) and muscular activity [upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and deltoid] were measured by an electromagnetic motion tracking system and surface electromyography, respectively. Subjects with SI had greater elevation of the scapula (11.9 mm, p < 0.005) and less peak scapular posterior tipping (10.6°, p < 0.02) than controls. In more severe subjects (amateur athletes), the elevation and posterior tipping of the scapula were correlated with an increase in the UT (R = -0.818, p = 0.025) and a decrease in SA (R = 0.772, p = 0.040) activity, respectively. Our results identified a characteristic compensatory scapular elevation to reduce impingement during arm elevation in subjects with SI. Assessing scapular elevation during arm elevation may be a useful functional marker for evaluating impingement status and associated muscle function. Additionally, SA and LT muscle strengthening may improve SI.
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