The reliability of methods to estimate the number and size of human motor units and their use with large limb muscles: common mistake

Excerpt

I was interested to read the paper by Piasecki M and colleagues published in the April 2018 issue of the Eur J Appl Physiol. Current methods for estimating muscle motor unit (MU) number provide values which are similar for muscles of widely differing size. They evaluated reliability of an alternative means of estimating MU number that takes into account differences in muscle size. They reported that intramuscular motor unit potentials (MUPs) were recorded and muscle cross-sectional area (CSA) was measured using MRI to provide a motor unit number estimate (iMUNE). This was compared to the traditional MUNE method, using compound muscle action potentials (CMAP) and surface motor unit potentials (sMUPs) recorded using surface electrodes. Test–retest reliability was evaluated with VL, tibialis anterior and biceps brachii. They reported that all measurements showed strong correlations between test and retest with r values from 0.84 to 0.91 (p < 0.0005). As the authors mentioned MUPs, sMUPs and CMAPs were highly reliable (r = 0.84–0.91) (Piasecki et al. 2018). …