[Motor unit potentials of the biceps muscle in comparing right and left parameters in right-handed subjects]

Motor unit potentials recorded by a concentric needle electrode in the right and left m. biceps brachii were statistically compared with regards to mean potential duration and amplitude. With the Wilcoxon-test the mean duration showed no statistically significant right/left difference, whereas the mean potential amplitude turned out to be significantly higher in the left m. biceps (Fig. 1, 2, table 1). The fibre density measured by a single fibre EMG electrode was found to be higher in the left m. biceps as well (1.23 as compared to 1.18 in the right). Therefore it is assumed that muscle fibre hypertrophy in muscles of the right arm in right-handed subjects leads to a decrease in fibre density within the motor units. The mean distance between active muscle fibres and electrode seems to be a more important factor with regards to the unit potential's amplitude than the muscle fibre diameter itself.