Relationships between SMES PSD and ACF main lobe width in localized muscle fatigue evaluation

Theoretical and experimental work carried out to investigate the relationships between the mean frequency (f_mean) of thesurface myoelectric signal (SMES) power spectrum, and the first zero crossing delay of its autocorrelation function (τ₀) are discussed. An inverse relationship exists between these two parameters if the active motor unit pool does not change during a contraction and the main effect responsible for the power spectrum variation is the decrease of the muscle fiber average conduction velocity. In such a case, it is possible to demonstrate that the slope of the regression line between f_mean and 1/τ₀ does not change during the contraction and is related to the shape of the SMES power spectrum. The percent variations of f_mean and τ₀ are equal and opposite. Experimental data supporting the theoretical results are presented, as well as some applications to the analysis of the SMES