Various shrug exercises can change scapular kinematics and scapular rotator muscle activities in subjects with scapular downward rotation syndrome

Abstract

Scapular dyskinesis, characterized by scapular downward rotation syndrome (SDRS) affects scapula-humeral rhythm and results in shoulder dysfunction. Previous study has led to the recommendation of standard shrug exercise to contend with SDRS and strengthen the upper trapezius (UT) muscle. However, few researchers have examined which shrug exercise is most effective. The aim of this research was to compare scapular kinematic changes and scapular rotator muscles activity across three different shrug exercises in SDRS. The amounts of scapular downward rotation were measured by a caliper and the scapular upward rotation angle was measured using two digital inclinometers. Surface electromyography was used to measure EMG amplitude from the UT, lower trapezius (LT), serratus anterior (SA), and levator scapula (LS). Seventeen subjects with SDRS were recruited for this study. The subjects performed three shrug exercises with 30° shoulder abduction (preferred shrug, frontal shrug, and stabilization shrug). The stabilization shrug showed a significantly greater scapular upward rotation angle compared with the preferred shrug (P=0.004) and frontal shrug (P=0.006). The UT activity was significantly greater in the frontal shrug than in the preferred shrug (P=0.002). The UT/LS muscle activity ratio was also significantly greater in the frontal shrug than in the preferred shrug (P=0.004). The stabilization shrug should be preferred to enhance the upward rotation angle. In addition, the frontal shrug can be used as an effective method to increase UT activity and to decrease LS activity in SDRS.

Keywords: Frontal plane; Spinal stabilization; Upper trapezius.