The function of brachioradialis.

PURPOSE The function of the brachioradialis muscle is controversial. The objective of this study was to determine primary and secondary functions of the brachioradialis under various loading tasks as measured by EMG. METHODS Ten healthy individuals (9 men, 1 woman; average age, 34 years +/- 10; average height, 175 cm +/- 7; average weight, 76 kg +/- 13) performed elbow flexion with the forearm in 1 of 3 positions (neutral, pronation, and supination) with 4 different loads (0, 22, 45, and 67 N). The elbow was flexed to 90 degrees as the volunteers performed 2 separate movements: (1) from full supination to neutral and (2) from full pronation to neutral using 4 different loads (0, 9, 18, and 27 N). Each movement started and ended in supination and pronation, respectively. Fine-wire EMG electrodes were placed in the brachioradialis, and kinematic data were collected using an electromagnetic motion analysis system. The EMG data were reported as a percentage of maximal voluntary isometric contraction and were ensemble averaged from 5 trials of each exercise condition for statistical analysis. RESULTS No difference in muscular activation was found during elbow flexion tasks in the 3 forearm positions. Significantly greater activation was found during concentric (23% maximal voluntary isometric contractions +/- 5% maximal voluntary isometric contractions) than during eccentric (11% maximal voluntary isometric contractions +/- 5% maximal voluntary isometric contractions) phases during elbow flexion. Brachioradialis mean activity during concentric pronation and eccentric supination with the heaviest loads 18 and 27 N was significantly greater than activity during concentric supination and eccentric pronation. CONCLUSIONS The greatest EMG activity recorded from the brachioradialis occurs during elbow flexion tasks regardless of forearm position indicating that the primary function of the brachioradialis is as a consistent elbow stabilizer during flexion tasks. During rotational tasks, more EMG activity was recorded during pronation compared with that during supination tasks indicating a secondary function of the brachioradialis as a pronator.