| Summary: | 碩士 === 國立陽明大學 === 物理治療研究所 === 93 === Background and purpose: Rotator cuff and scapular stability play important roles in the overarm throwing motions, especially from the late-cocking to the deceleration phases. Recent studies suggested a functional ratio of high eccentric torque for external rotation relative to concentric torque for internal rotation for optimal dynamic stability of the glenohumeral joint during overarm throwing. Additionally, the scapula needs to become a stable base for the shoulder to maintain in abduction of 90~110�a throughout the throwing motion. A proper functional ratio for the rotator cuff and sufficient scapular stability have been indicated as crucial in preventing shoulder injuries during overarm throwing motions. But few studies have examined the associations between shoulder symptoms and functional ratios or scapular stability in baseball players. The aim of this study was to investigate the functional ratio of the rotator cuff and scapular stability in Taiwanese baseball players with and without shoulder symptoms. Methods: Eighty-one amateur baseball players (45 without and 36 with shoulder symptoms) were recruited to perform isokinetic tests for functional ratios of the rotator cuff and clinical tests for scapular stability that included scapular positioning (protraction and LSST), neuromuscular control (setting phase in the scapulohumeral motion, position sense of the scapular retraction, and strength of the scapular muscles). To comply with the general rules of clinical scapular assessments, we used side-to-side difference for the observed scapular measures (scapular protraction, setting phase and position sense of scapular retraction). The test was deemed positive when the dominant side showed a difference of over 1 cm in scapular protraction or over 10% in the setting phase or the position sense of scapular retraction as compared to the non-dominant data. Analyses of covariance (ANCOVAs) were used for comparing the continuous variables and the Chi Squares tests for categorical variables between the baseball players with and without shoulder symptoms (α<0.05). Results: The strength of lower trapezius muscle was significantly weaker in the players with shoulder symptoms. The other clinical or isokinetic tests showed no differences between players with or without shoulder symptoms. Conclusions: The lower trapezius was weaker in the symptomatic baseball players, and this might affect their scapular stabilization and overarm performance. Clinical Relevance: Training the strength of the scapular muscles, especially the lower trapezius muscle is important in the training and rehabilitation programs of the players with shoulder symptoms.
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