An electromyographic study of weight-bearing at the elbow joint.

The purpose of this study was to investigate the roles of specific muscles in supporting the elbow joint in full extension during a static weighted situation. Various forearm positions from pronation through supination were used to determine carrying efficiency by monitoring muscle activity. Fine-wire electrodes were inserted into the biceps brachii, brachialis, brachioradialis, and medial head of the triceps in order to record the action potentials of these muscles. The forearm was studied in four different positions: (1) prone, (2) relaxed or natural, (3) semiprone, and (4) supine. These positions were monitored by an elgon potentiometer. The loads for the subjects were from 2-20 kilograms. Reliability coefficients of repeated trials were significantly positive. It was concluded that the muscles played an important role in supporting the elbow in full extension during a detracting force and that there was no significant difference between the muscular activity of males and females. Of the four positions studied, the supine position required the most activity suggesting an inefficient carrying position. The triceps was significantly more active when the arm was in the prone position. The roles of muscle groups in supporting the fully extended elbow joint during a detracting force changed as the forearm moved between supination and pronation. The elbow flexors were most active in the supine position, while the elbow extensor muscle was most active in the prone position.