Prior muscle activation affects the compound muscle action potential

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