The effect of epoch length on the electromyographic mean power frequency and amplitude versus time relationships

Abstract

The electromyographic (EMG) mean power frequency (MPF) and amplitude versus time relationships are commonly used to characterize localized muscle fatigue.

Purpose: The purpose of this study was to compare the effect of epoch length on the individual and mean slope coefficients and y-intercepts resulting from the EMG MPF and amplitude versus time relationships of the vastus medialis (VM) muscle during fatiguing isometric muscle actions at 30 and 75% of maximum voluntary isometric contraction (MVC).

Methods: Eight adults performed two continuous, isometric muscle actions of the leg extensors at 30 and 75% MVC to exhaustion. Six, 5.0 s epochs of the surface EMG signals were recorded from the VM during each minute. Epoch lengths of 0.5, 1.0, and 2.0 s were selected from the middle of each 5.0 s epoch. Linear regression was used to estimate the slope coefficient and y-intercept values for the EMG MPF and amplitude versus time relationships for each epoch length (0.5, 1.0, 2.0, and 5.0 s) and subject.

Results: There were no significant differences between epoch lengths for the individual or mean slope coefficients or y-intercepts (EMG MPF and amplitude versus time relationships).

Conclusion: This study indicated that epochs of 0.5 - 5.0 s resulted in the same characterization of EMG (MPF and amplitude) versus time relationships during isometric muscle actions.