Objective: To study excitability of single motor units (MUs) using high-density surface-EMG.
Methods: Motor unit action potentials (MUAPs) were evoked by submaximal stimulation of the median nerve at the wrist and recorded with a 9 × 14 electrode grid on the skin overlying the thenar muscles. For excitability tests of single MUs, the most optimal specific single-channel surface-EMG signal was selected based on the spatiotemporal profile of single MUs.
Results: Axonal excitability measures were successfully obtained from 14 single MUs derived from ten healthy subjects. Selecting the optimal single-channel surface-EMG signals minimized interference from other single MUs and improved signal-to-noise ratio. The muscle fiber conduction velocity (MFCV) could also be derived from the unique spatiotemporal profile of single MUs.
Conclusion: High-density surface-EMG helps to isolate single MUAP responses, making it a suitable technique for assessing excitability in multiple single motor axons per nerve.
Significance: Our method enables the reliable study of ion-channel dysfunction in single motor axons of nerves without any requirement for specific conditions, such as prominent MU loss or enlarged MUAPs due to collateral sprouting.

Excitability testing, High-density surface-EMG, Single human motor axons, Single motor unit action potentials
dx.doi.org/10.1016/j.clinph.2018.04.754, hdl.handle.net/1765/108847
Clinical Neurophysiology
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Erasmus MC: University Medical Center Rotterdam

Sleutjes, B.T.H.M, Drenthen, J, Boskovic, E. (Ernest), van Schelven, L.J. (Leonard J.), Kovalchuk, M.O. (Maria O.), Lumens, P.G.E. (Paul G.E.), … Franssen, H. (2018). Excitability tests using high-density surface-EMG. Clinical Neurophysiology, 129(8), 1634–1641. doi:10.1016/j.clinph.2018.04.754