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Updated: Jul 5, 2026
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Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation
Published on: September 13, 2015
Pulse charge and not waveform affects M-wave properties during progressive motor unit activation.
A Botter1, R Merletti, M A Minetto
1Laboratory for Engineering of the Neuromuscular System (LISiN), Department of Electronics, Polytechnic of Turin, Turin, Italy.
Summary
This study found that the charge of electrical stimulation, not the waveform, determines motor unit activation. A triangular waveform reduced discomfort during neuromuscular electrical stimulation (NMES).
Area of Science:
- Neuromuscular Physiology
- Biomedical Engineering
Background:
- Neuromuscular electrical stimulation (NMES) is used to activate motor units (MU).
- Optimizing NMES protocols requires understanding factors influencing MU recruitment and subject comfort.
Purpose of the Study:
- To investigate how different electrical stimulation pulse waveforms affect M-wave responses and motor unit activation.
- To determine the impact of stimulation charge and waveform on subject discomfort during NMES.
Main Methods:
- Surface electromyography (sEMG) was used to record M-waves from the biceps brachii in 10 subjects.
- Three monophasic waveforms (triangular, square, sinusoidal) were applied with increasing current intensities.
- Stimulation parameters included a 304-microsecond pulse duration and 20 Hz frequency.
Main Results:
- Motor unit activation, measured by M-wave average rectified value, correlated with injected charge, independent of waveform.
- Motor units were recruited in order of increasing conduction velocity as stimulation charge increased.
- Subjects reported less discomfort with the triangular waveform compared to square and sinusoidal waveforms.
Conclusions:
- Injected charge is the primary determinant of motor unit activation during NMES.
- Waveform shape influences subject comfort, with triangular waveforms being less uncomfortable.
- Optimizing NMES protocols should consider both stimulation charge and waveform for effective motor unit recruitment and subject tolerance.
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