Impact of Shoulder Shrugging Motion on Muscles Surrounding the Shoulder Joint during Forward Elevation of the Upper Limb

SHIZUKUDA Kensuke, HATA Yukihiko, ISHIGAKI Norio, TAKAHASHI Tomoaki, TAJIMA Yasuhiro, MIMURA Ryouko, MAEDA Shouko

doi:10.2185/jjrm.65.940

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.

Impact of Shoulder Shrugging Motion on Muscles Surrounding the Shoulder Joint during Forward Elevation of the Upper Limb

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