Effects of different movement directions on electromyography recorded from the shoulder muscles while passing the target positions

Purpose: We compared electromyography (EMG) recorded from the shoulder joint muscles in the same position for different movement directions.

Methods: Fifteen healthy subjects participated. They performed shoulder elevation from 0° to 120°, shoulder depression from 120° to 0°, shoulder horizontal adduction from -15° to 105°, and shoulder horizontal abduction from 105° to -15°. The target positions were 90° shoulder elevation in the 0°, 30°, 60°, and 90° planes (0°, 30°, 60°, and 90° positions). EMG signals were recorded from the supraspinatus (SSP) muscle by fine-wire electrodes. EMG signals from the infraspinatus (ISP), anterior deltoid, middle deltoid, and posterior deltoid muscles were recorded using active surface electrodes.

Results: During elevation and horizontal abduction, the SSP showed significantly higher activity than that shown during depression and during horizontal adduction in the 0°, 30°, and 60° positions. During elevation, the ISP showed significantly higher activity than during depression and during horizontal adduction in the 90° position. During horizontal abduction, the ISP showed significantly higher activity than during depression in the 90° position.

Conclusions: When the movement tasks were performed in different movement directions at the same speed, each muscle showed characteristic activity.