Effects of electromyographic processing methods on computer-averaged surface electromyographic profiles for the gluteus medius muscle.

The objective of this study was to demonstrate how two different linear envelope detectors, as used in the quantification of surface electromyographic (EMG) signals, can lead to differences in the properties of observed computer-averaged EMG profiles. Eight healthy male subjects, aged 24 to 32 years, participated in the study. Computer-averaged EMG profiles for the gluteus medius muscle were recorded at a free-walking cadence and at stepping frequencies of 78 and 120 steps/min, using detectors with 3- and 25-Hz cutoff frequencies simultaneously. The 3-Hz filtered EMG profiles proved to be smoother, to exhibit a significantly lower cycle-to-cycle variability, and to have a greater time lag with respect to the original unprocessed EMG signal than the 25-Hz filtered EMG profiles. The observed intersubject variability also was lower for the 3-Hz filtered EMG profiles than for the 25-Hz filtered EMG profiles. The results indicate that comparison of EMG profiles recorded with different detectors is difficult. A standard detector may solve this difficulty.