MORPHOLOGICAL AND STRENGTH CHARACTERISTICS OF THE ROTATOR CUFF AND DELTOID MUSCLES IN COLLEGIATE BASEBALL PLAYERS / 体力科学

ABSTRACT

The purpose of this study was to investigate the influence of a shoulder injury on rotator cuff muscle thickness and shoulder muscle strength in baseball players. Based on orthopedic medical checks performed by a doctor for 57 male collegiate baseball players, two groups, the pain-free normal group (NOR group, n=19) and the impingement test positive group (IMP group, n=17) volunteered to participate in the study. Muscle thickness of the supraspinatus, infraspinatus and posterior deltoid muscles was measured bilaterally using a B-mode ultrasound apparatus (SSD-500, Aloka) with a 5-MHz transducer. Isometric shoulder abduction strength was measured bilaterally with a hand-held dynamometer in the sitting position with the arm at 45 degrees abduction, and shoulder external and internal rotation strength were measured bilaterally with an isokinetic dynamometer in the sitting position with the upper arm at 90 degrees abduction.<BR>When the two groups were compared, the NOR group showed significantly greater values on the dominant side than on the non-dominant side for muscle thickness of the posterior deltoid. However, the IMP group showed significantly greater values on the non-dominant side than on the dominant side of muscle thickness of the supraspinatus, the muscle strength with the abduction and external rotation (300 deg/sec) and external internal rotation strength ratio (180 deg/sec) .<BR>Also, the IMP group had a significantly weaker dominant/non-dominant ratio of supraspinatus muscle thickness (p<0.05) and abduction strength than the NOR group (p<0.01) .<BR>These results suggest that baseball players with positive impingement show both a morphological and functional decline in the supraspinatus muscle. The dominant side supraspinatus weakness observed in the IMP group of this study may reflect muscle atrophy and chronic fatigue.