Antagonist surface electromyogram decomposition and the case of the missing motor units

Reece and Herda (J Neurophysiol 125: 2094-2106, 2021) reported that an antagonist muscle exhibited an organized motor unit (MU) recruitment scheme during isometric elbow flexion contractions. This control scheme, however, differed from the typical MU control scheme in that MU firing rates did not change between force levels (40% and 70% maximal voluntary contractions) in the triceps brachii when it acted as an antagonist to isometric elbow flexion. Here, we suggest technological considerations with evidence that may have affected these findings. In addition, we highlight how this paper offers a promising starting point from which further insight into antagonist MU behavior can be gathered noninvasively and suggest future research directions to improve our understanding of MU activity of antagonist muscles in the upper limb.