Sensitivity of the surrogate analysis method to synchronization and conduction velocity of muscular fibers

Abstract This paper shows that conduction velocity (CV) and motor unit action potential (MUAPs) synchronization affects the results of Surrogate Analysis (SA) of the surface electromyography (sEMG) signal. It will be verified if the SA can extract information from the sEMG signal. Also, it is the first time that the SA is interpreted from a physiological point-of-view. To illustrate the relationships between the CV, the synchronization and the SA, a simple dipole-based model for (sEMG) signal simulation is used. It is composed of multiple fibers superposed at the same location, leaving aside any complex geometrical considerations, but putting the emphasis on the timing of the MUAPs firing. Single-pulse synchronization as well as impulse train synchronization are studied. To highlight the difference between spectral (linear) features, nonlinear features and SA relation with the model parameters, the Median Frequency (MDF), the Kurtosis, the Higuchi’s Fractal Dimension (FD) and the FD based SA are compared. The simulation results show that the SA is jointly influenced by CV and the MUAPs synchronization, almost in a multiplicative way. These relations are also more pronounced for an impulse train than for a single pulse. Overall, the SA is shown to be a good feature to consider for CV and MUAPs synchronization estimation. It is moreover uncorrelated with spectral features and moderately with nonlinear features. These findings can be used to 1) help evaluate the CV and MUAPs synchronization and 2) interpret the result of the surrogate analysis.