Electromyography tension and frequency spectrum analysis at rest of some masticatory muscles, before and after TENS

On a population of 52 subjects surface electromyographic recordings were performed of 13.5 sec. of duration before and after ULF (Ultra Low Frequency)-TENS relaxing procedure, while they were holding their mandible at rest. For each recording the average of tension (IEMG) and the median of frequency was calculated. To compute the median of frequencies a Fast Fourier Transformer (FFT) was applied. In order to compare modifications induced by the 45' ULF-TENS relaxing procedure, so that the influence of ULF-TENS could be well isolated from any influence due simply to the time passing between one recording and another, three recordings were performed at different times: the first at time 0', the second at time 0' + 20', and only the third after TENS, time 0' + 20' + 45'. The results of the study permit us to draw the following conclusions: 1. it is confirmed that ULF-TENS can decrease muscle IEMG; 2. the study of the IEMG and frequency of the electromyographic signal at rest can be carried out starting from a window whose size and position in the 13.5 sec. of recording is arbitrary; 3. there is no connection between IEMG and frequency: in other words, at rest, there is no necessary correspondence between high or low IEMG and a high or low frequency values; 4. on application of the neurodiagnostic test of ULF-TENS, the IEMG of the electromyographic signal decreases, while the frequency of the signal remains unchanged. These last two observations permit us to hypothesize that the IEMG and the frequency of the electromyographic signal reflect some different and independent characteristics of the electrical activity of the muscle at rest.