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

Unlabelled: 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.