[Frequency analysis (FFT) of electromyography and development of the quiet period in the masticatory muscle discharge].
The purpose of this study was to analyze the control mechanism of quiet period (silent period, QP) in myoelectric signals of the masseter and the anterior part of temporalis by the measure of frequency analysis (FFT) and the power spectra, according to the bite force developement. Surface myoelectric signals of te masseter and the temporalis (both sides) of nine human subjects with normal occlusion were recorded during biting movements. Subjects were asked to increase their forces rapidly to their maximum bite force levels at the decided three rate (0.5sec, 1.0sec and 2.0sec) respectively. QPs (duration; 10 approximately 70ms) were observed (occurrence rate; 44%) almost simultaneously in four muscles at both experimental conditions of the high accelerative movements (0.5sec) and of low levels of bite force remarkably. Frequency analyses were carried out by means of Fast Fourier Transform about myoelectric signals for the period of each 50ms before and after QP occurrence. In the higher frequency bands (200 approximately 480Hz), power spectra "AFTER QP" were distributed with high energy density, whereas "BEFORE QP" were characterized in low frequency bands (20 approximately 180Hz) with low energy. By these analysis, following results were discussed such as that the recruitment of phasic motor units (high frequency bands of power spectra) appeared with fast rate coding in the EMG of QP occurrence, and it should be natural for the neural switching mechanism to be activated in QP occurrence in order to transfer from tonic units to phasic ones of EMG.
D000328:Adult; D003201:Computers; D004576:Electromyography; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D008409:Mastication; D008410:Masticatory Muscles / Q000502:physiology*; D010507:Periodicity; D011999:Recruitment, Neurophysiological; D013703:Temporal Muscle / Q000502:physiology*