POWER SPECTRAL CHANGES OF THE SUPERIMPOSED M WAVE DURING ISOMETRIC VOLUNTARY CONTRACTIONS OF INCREASING STRENGTH

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Abstract

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. Muscle Nerve 51: 580–591, 2015

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