Effect of Neck Rotating Directions on the Muscle Activity of Upper and Lower Trapezius during Shoulder External Rotation

Abstract

Purpose: This study examined the effects of the directions of neck rotation on the muscle activity of the upper trapezius and lower tra pezius while rotating a shoulder externally. Methods: Twenty-five healthy males participated in this study. The subjects were asked to rotate their shoulder externally with 90° shoulder abduction and 90° elbow flexion in three different neck rotations (neutral, ipsilateral, and contralateral) in the prone position. The muscle activities of the upper and lower trapezius were measured using surface electromyography. One way repeated measures ANOVA was used to compare the muscle activity of the upper and lower trapezius depending on the different neck turning directions. Results: In the upper trapezius, turning the neck in the ipsilateral direction while turning a shoulder externally decreased the muscle ac tivity significantly, but the muscle activity was increased significantly by turning the neck in the contralateral direction. On the other hand, in the lower trapezius, turning the neck in the ipsilateral direction increased the muscle activity significantly, but the muscle activ ity was decreased significantly by turning the neck in the contralateral direction decreased it significantly. Conclusion: When someone has an imbalance of shoulder function, turning the neck in the ipsilateral direction while turning the shoul der externally in the prone position is effective in decreasing the activity of the upper trapezius and increasing the activity of the lower trapezius. Therefore, these results could be used as basic evidence for researching patients with shoulder problems.