Wavelet frequency-temporal relative phase pattern analysis for intermuscular synchronization of dynamic surface EMG signals

Cross-correlation is often used as the primary technique to compare two biological signals. Cross-correlation is an effective means to measure the synchronization of two signals assuming the relative phases of all frequencies are distributed linearly, that is, a group delay. The group delay assumption imposes an unfavorable restriction on signals with varying relative phase correlation at different frequencies. The traditional Fourier technique provides phase information for each frequency component, but it is not suitable for biological signals with non-stationary statistics. The application of a wavelet based phase analysis technique is discussed in this study. The frequency decomposition and temporally localized nature of the wavelet transform provides localized phase-frequency information for two signals. The merits and weaknesses of using the wavelet relative phase pattern for determining the synchronization of surface electromyographic signals from two muscle sites is discussed.