FORCE MEASUREMENT OF BRACHIORADIALIS BY ELECTROMYOGRAPHY

Abstract

Aim: To develop a database of the force generated by brachioradialis muscle (BR) using IEMG.

Methods: The 32 BR muscles of 12 young male and four young female adults were studied using the MedTronic functional diagnostics key point EMG machine. Two self adhesive surface electrodes were placed 3mm apart over the BR belly and a third earth electrode over the radial styloid process. The subject’s arm was at the side of the trunk, the elbow flexed to 90 degrees and the forearm strapped in neutral rotation. Recordings were taken over a five-second voluntary maximum isometric elbow flexion and the force of the contraction measured from the rectified and integrated tracing (mv.ms). Four recordings were taken for each arm; wrist in neutral and at maximum passive flexion, with a two-minute rest between recordings. Recordings were repeated after minimum of 24 hours later.

Results: There was large inter-subject variability with a range of values recorded between 14 685 and 278 533 mv.ms with an average of 99 472 for the wrist in neutral and 93 038 with the wrist flexed in males and 53 292 and 57 224 respectively for females. However, intra-subject variability was low (co-efficient of variation, CV 8 to 11%) and good repeatability (CV 6 to13%). There was no significant statistical difference with the wrist either in neutral or fully flexed.

Conclusions: BR is the key muscle for hand reconstruction in tetraplegia but it has not been possible until now to test its force objectively in isolation from other elbow flexors. Although the results from the study demonstrated a wide range of values for the BR muscle the consistent repeatability probably reflected different involvement of the BR muscle in elbow flexion. If verified, it would indicate that tetraplegics who have low IEMG values should benefit from specific strengthening exercises prior to transfer surgery.