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Updated: Jan 28, 2026

Electrophysiological Motor Unit Number Estimation MUNE Measuring Compound Muscle Action Potential CMAP in Mouse Hindlimb Muscles
Published on: September 25, 2015
Prior muscle activation affects the compound muscle action potential
Gordon W Peterson1, Bryan E Tsao1, Laura D Nist1
1Department of Neurology, Loma Linda University School of Medicine, Loma Linda, CA.
Introduction:
This study was performed to evaluate the effect of prior voluntary activation of a muscle on the subsequently-recorded compound muscle action potential (CMAP).
Methods:
The CMAPs from the hypothenar, thenar, and extensor digitorum brevis muscles were recorded in 6 healthy volunteers at rest and for up to 30 min following 5 separate epochs of up to 20 s of voluntary muscle activation.
Results:
There was consistent, significant (P < 0.02) enhancement of the negative area, amplitude, and duration of the CMAP after activation. The enhancement was maximal, up to 144% of baseline, within about 1 min post-activation; thereafter, the CMAP gradually returned to baseline over about 15 min.
Discussion:
Activation of a muscle within several minutes prior to testing enhances the subsequently-recorded CMAP. This observation highlights prior muscle activation as a physiological variable that influences the size of the CMAP during motor nerve conduction studies. Muscle Nerve, 2019.
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