Effect of overhead lifting on neck and shoulder muscle activity and upper extremity joint angles

The purpose of this study was to determine the effects of varying amount of lifted weight on upper extremity joint angles and muscle activity of the neck and shoulder. Two-dimensional elbow and shoulder kinematics of overhead lifting were determined, and simultaneously surface electromyographic (EMG) data from the upper trapezius and sternocleidomastoid muscles were collected. Results show that as lifted weight increased, the EMG activity of both muscles increased accordingly. Increasing the weight also resulted in increased maximum elbow joint angle and decreased maximum shoulder joint angle, but the effects were not significant. Shoulder angle and muscle activity were highly correlated. The correlation coefficients ranged from 0.39 to 0.75 for the trapezius muscle and from 0.38 to 0.42 for the sternocleidomastoid muscle. The elbow joint angle had low to no influence on shoulder and neck muscle activity.