The purpose of this study was to elucidate the effects of “shoulder girdle training” that is used to correct scapular muscle imbalance. We investigated 100 shoulders in 50 healthy volunteers free of any complaints related to the shoulder joint. In the posture for performing the infraspinatus test, male volunteers held a 5-kg load and female volunteers held a 3-kg load for 3 s thrice, and the muscular activity of the trapezius muscle was simultaneously measured. Next, shoulder girdle training was performed for 5 s twice, followed by muscle activity measurement in the same manner described above. Muscle activity levels before and after this training and also between the dominant and non-dominant sides were compared. The shoulder girdle training significantly reduced the level of muscle activity of the upper fibers of the trapezius muscle and significantly increased the level of muscle activity of the middle and lower fibers of the trapezius muscle (both p<0.05). Moreover, the levels of muscle activity of the upper, middle, and lower fibers of the trapezius muscle were significantly higher on the dominant side than on the non-dominant side (p<0.05).

　　Rotator cuff repair provides favorable outcomes for range of motion of the shoulder joint and repair of the cuff. However, we often have patients for whom shoulder elevation is difficult due to failure to improve shoulder shrugging motion. This study investigated how the shoulder shrugging motion affects activity patterns of the muscles surrounding the shoulder joint. Subjects were 50 shoulders in 50 young healthy volunteers free from shoulder joint complaints (27 men, 23 women; mean age, 26.3±4.3 years). The subjects were placed in the lateral position with the dominant arm facing upwards and suspended with a sling. They performed two types of movements: forward elevation of the arm with no particular instructions (group N) and forward elevation combined with shoulder shrugging (group S). Simultaneously, the activity of the anterior, middle, and posterior fibers of the deltoid muscle and of the upper, middle, and lower fibers of the trapezius muscle of the dominant upper limb were measured by surface electromyography and compared between the two groups. In the trapezius muscle, upper fiber activity was more enhanced in group S than in group N, whereas lower fiber activity was more strongly suppressed in group S. However, the anterior and middle fiber activity of the deltoid muscle was more strongly suppressed in group S than in group N. Thus, it was observed that an elevation pattern with shoulder shrugging reduces the strength of forward flexion.