The use of cross correlation function in onset detection of electromyographic signals

The use of electromyographic signals (EMG) to study muscle coordination requires robust methods to accurately detect EMG onset, especially when investigating anticipatory actions or the order of muscle recruitment during motion analysis. Some studies have used the normalized cross-correlation function (CCF) for estimating activation delays. This study aimed at evaluating the use of CCF to determine time delays between pairs of EMG, in comparison with a visual detection of EMG onset. 372 isotonic motion EMG from four different muscles from 31 subjects were analyzed during the movement of prone hip extension with knee extension. All comparisons including gluteus maximus muscle resulted with significant differences between methods. This found suggest that the use of CCF for evaluating delay in muscular activation onset requires caution, since this function takes into account the whole signal patterns and not only the EMG onsets.