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Updated: Apr 26, 2026

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation
Published on: September 13, 2015
Power spectral changes of the superimposed M wave during isometric voluntary contractions of increasing strength
Javier Rodriguez-Falces1, Nicolas Place
1Universidad Pública de Navarra D.I.E.E., Department of Electrical and Electronical Engineering, Campus de Arrosadía s/n., 31006, Pamplona, Spain.
Introduction:
We examined the power spectral changes of the compound muscle action potential (M wave) evoked during isometric contractions of increasing strength.
Methods:
Surface electromyography (sEMG) of the vastus lateralis and medialis was recorded from 20 volunteers who performed 4-s step-wise isometric contractions of different intensities. A maximal M wave was elicited by a single stimulus to the femoral nerve and superimposed on the voluntary contractions. The spectral characteristics (Fmean and Fmedian) of sEMG and M-wave signals were calculated.
Results:
M-wave spectral indicators increased systematically with contraction intensity up to 60% MVC and then leveled off at higher forces. Over the 10-60% MVC range, the increase in spectral indicators was 3 times higher for M waves (36%) than for sEMG (12%).
Conclusions:
The consistent increase in M-wave spectral characteristics with force is due to the fact that the number of motor units recruited by the superimposed supramaximal stimulus is approximately stable.
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