The Role of the Muscle Brachioradialis in Elbow Flexion: An Electromyographic Study.

Background: In the classical conception, the brachioradialis is a forearm supinator. The hypothesis of this study was that, at least in certain positions of elbow flexion and forearm rotation, the brachioradialis is, along with the biceps and brachialis, one of the main elbow flexors.

Methods: Fifteen young healthy male volunteers participated in this research. The activities of the biceps, brachialis and brachioradialis muscles were studied using surface electromyography, while the subjects were performing elbow flexions/extensions with as much strength as possible, forearm in neutral position, then in full pronation, then in full supination. The elbow flexion torques were isokinetically measured at 60°/sec for an arc of 120°.

Results: The biceps, brachialis and brachioradialis muscles were electromyographically very active throughout resisted elbow flexion, in all three investigated positions of forearm rotation. At certain positions, the electromyographic activities were much higher than the maximal voluntary contraction signal. For what concerns specifically the brachioradialis, in all three forearm rotation investigated positions, the activity curve demonstrated a slow increase during the first part of elbow flexion, reaching in 73.3% of subjects its peak at the end of flexion; in the remaining 26.7%, the brachioradialis had a flat activity without significant peak. The activity was slightly higher in supination.

Conclusions: This study indirectly supports the idea that the brachioradialis is one of the main elbow flexors, especially when the elbow flexion is done with the forearm in supination. This observation could be important in clinical elbow and wrist surgical practice.