The Motor Unit Innervation Process Correlation and Its Effects on EMG Applications

It has often been assumed in EMG modeling and signal processing applications, that the motor unit action potential trains (MUAPT) of concurrently active motor units during voluntary contractions are not correlated. However, motor unit synchrony, or motor unit innervation process (MUIP) correlation, which implies MUAPT correlation, has been accepted as a common phenomenon in voluntary contractions. The impact of this MUIP correlation in applications which assume its absence has not been thoroughly studied. In this paper, simulated data with different degrees of MUIP correlation are applied to investigate this issue. Simulation results show that MUIP correlation may compromise the assumption of uncorrelated MUAPTs (depending on recruitment level), and MUIP correlation has a downwards spectrum compression effect on the power spectrum of EMG