Electromyographic response of the elbow flexors to a changing, dislocating force

The electromyographic (EMG) outputs of the biceps brachii, brachialis, and brachioradialis muscles of 14 subjects were monitored during the application of an externally generated, dislocating force across the elbow joint. Subjects were seated in an apparatus designed to maintain the right upper extremity at 90 degrees shoulder flexion and 180 degrees elbow extension. The dislocating force was increased from 0-22 Newtons (N) at an average rate of 2N/sec to determine if a minimum load were necessary before muscles would be activated. Although no muscle was found to be significantly more active than any other over the entire load range, post hoc analysis showed that both the brachialis and brachioradialis were significantly more active at loads above 18N than below. The biceps brachii showed no significant increase in activity. The practice of strengthening muscles as a means of protecting joint integrity can be questioned by these results since the muscles under study did little to resist elbow joint dislocation at loads up to 18N.