Scapular Displacement and Its relationship to Shoulder Internal and External Rotator Muscle Function

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Alterations in scapular position and movement often referred to scapular dyskinesis are hypothesized to bear a direct relationship to scapular stability and the generation of muscular force production. However, there is a lack of data regarding the influence of the scapular malposition to the shoulder muscle function. PURPOSE: To examine the scapular displacement during the sitting hand press up test and its relationship to shoulder internal and external rotator muscle function in Division III baseball players. METHODS: Total fifty-one Division III overhead athletes [12 female volleyball players (18.5±0.67 yrs, 70.79±9.29 kg, 173.25±6.65 cm) and 39 male baseball players (19.7±1.3 yrs, 83.45±12.83 kg, 180.47±7.42 cm)] participated in the study. Scapular dyskinesis during the rest position and the sitting hand press up test was measured using the Hong's tool. Concentric internal and external rotation peak torques and time to peak torques were measured on the dominant arm at 60 degree/sec. Subjects were tested in the seated position with the shoulder abducted to 90° and the elbow flexed to 90°. The cutoff point for those with scapular kinesis and those not exhibiting winging is 1cm. RESULTS: The athletes with scapular posterior displacement (SPD)> 1cm exhibited significantly delayed time to peak torques (msec) in both internal and external rotation of shoulder (893.18±386.61 and 623.63±393.67 msec) compared to the athletes with SPD< 1cm (482.75±257.12 and 339.65±231.55 msec) (p<0.05). There were no differences in internal and external rotation peak torques between groups. CONCLUSION: The results of the study indicated that overhead athletes with scapular dyskinesis show delayed time to peak torques in shoulder internal and external rotation. The findings support the theory that the presence of scapular dyskinesis may be related to the delayed shoulder muscular force production.