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Dynamic Acromiohumeral Interval Changes During Scapular Plane Arm Motions, Melissa Deen Thompson

LSU Doctoral Dissertations

This purpose of this dissertation is to explore changes in the acromiohumeral interval during dynamic motion in the scapular plane. All of the experiments were completed in the Football Operations Athletic Training Room at Louisiana State University. The first experiment which investigated dynamic acromiohumeral interval changes in baseball players during a loaded and unloaded scaption exercise from 0°-75°, has been accepted for publication by the Journal of Shoulder and Elbow Surgery (in press, 2010). The mean acromiohumeral interval (AHI) for unloaded and loaded scaption decreased significantly (p<.001) from the arm at the side until 45° and loaded scaption narrowed AHI at 60° (p=.005) and 75° (p=.003). The second experiment investigates AHI and scapular upward rotation (SUR) changes in baseball and softball players during scaption exercises from 0°-75°. Significant load related narrowing of the AHI at 45°(p=.005), 60°(p=.001), and 75°(p<.001) and a significant load-position interaction (p=.001) at 0° and 75°was observed for all subjects. No gender differences in SUR or AHI were found. AHI and SUR displayed moderate positive correlations at 30° for both the unloaded scaption (r=.648, p=.001) and the loaded scaption (r=.445, p=.038) however, no significant relationships were present at 0°, 45°, 60° or 75°. The third experiment compared dynamic acromiohumeral interval and scapulohumeral rhythm changes in trained and untrained females during scaption exercises from 0°-90°. In general, AHI was maximal with the arm at the side and declined significantly (p<.001) during arm elevation until 60°, but increased significantly (p<.001) between 60° and 90°. Significant load related narrowing of the AHI at all positions (p<.05), a more negative SUR at 0° (p<.001) and a more positive SUR at 90° (p=.009) was observed for all subjects. Female athletes had significantly stronger external rotators (p<.001), larger overall AHI (p=.003) and more SUR (p=.008) than untrained females. Significant positive correlations (p<.05) between AHI and SUR were observed at 0°, 30°, and 60° during both loaded and unloaded scaption.