Rectification of the EMG signal impairs the identification of 4 oscillatory input to the muscle 5 6

26 Rectification of EMG signals is a common processing step used when performing EEG-EMG 27 coherence and EMG-EMG coherence. It is well known, however, that EMG rectification alters 28 the power spectrum of the recorded EMG signal (interference EMG). The purpose of this study 29 was to determine whether rectification of the EMG signal influences the capability to capture the 30 oscillatory input to a single EMG signal and the common oscillations between two EMG signals. 31 Several EMG signals were reconstructed from experimentally recorded EMG signals from the 32 surface of the first dorsal interosseus muscle and were manipulated to have an oscillatory input 33 or common input (for pairs of reconstructed EMG signals) at various frequency bands absolute integral and normalized integral of power, peak power, and peak coherence (for pairs of 36 EMG signals) was quantified from each frequency band. The power spectrum of the interference 37 EMG accurately detected the changes to the oscillatory input to the reconstructed EMG signal, 38 whereas the power spectrum of the rectified EMG did not. Similarly, the EMG-EMG coherence 39 between two interference EMG signals accurately detected the common input to the pairs of 40 reconstructed EMG signals, whereas the EMG-EMG coherence between two rectified EMG 41 signals did not. The frequency band from 12-30 Hz in the power spectrum of the rectified EMG 42 and the EMG-EMG coherence between two rectified signals was influenced by the input from 43 100-150 Hz but not from the input from 12-30 Hz. The study concludes that the power spectrum 44 of the EMG and EMG-EMG coherence should be performed on interference EMG signals and 45 not on rectified EMG signals because rectification impairs the identification of the oscillatory 46 input to a single EMG signal and the common oscillatory input between two EMG signals.