A simulation study of unwhitened versus whitened EMG amplitude estimation

Amplitude estimates of simulated surface electromyograms (EMGs) were studied using both unwhitened and whitened EMG amplitude estimators. Constant-effort non-fatiguing EMGs were simulated as the superposition of simple synthetic motor unit action potential trains (MUAPTs). Each MUAPT was formed from random firings of randomly shaped motor unit action potentials. Two aspects of unwhitened vs. whitened amplitude estimators were studied: (1) the relationship between the mean value of the EMG amplitude estimate vs. the level of contraction and (2) the signal-to-noise-ratio (SNR) performance of the EMG amplitude estimate. It was found that the relationships between estimated EMG amplitude vs. MUAPT firing rate and the number of MUAPTs were not altered by whitening. However, the performance of whitened amplitude estimators was markedly better. These results suggest that whitening can provide a higher fidelity EMG amplitude estimate without distorting the relationship between EMG and the mechanical output of the muscle.