Effect of sustained contraction on motor unit action potentials and EMG power spectrum of human masticatory muscles.
The sequelae of a sustained clench are incompletely understood. Our experimental questions were to compare the responses of men and women, to compare masseter and anterior temporalis muscles, and to test hypotheses for the reduction of the median frequency of power spectra. We recorded duration, amplitude, number of phases, and area of the motor unit action potential before and after a sustained clench and the median frequency of the electromyographic power spectrum in 41 subjects. After the clench, the median frequency was lower, the action potential duration longer, the number of phases increased, and the area larger, but the amplitude was not different. Males and females failed to differ. Compared with the temporalis, the masseter had a lower median frequency, longer duration, larger number of phases, and increased area. Our results are consistent with a decrease in the conduction velocity of the muscle action potential as an explanation of the spectral shift.
Department of Oral Medicine and Diagnosis, College of Dentistry, Kangnung National University, Korea.
J W
JW
Chung
C
C
Kim
W D
WD
McCall
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D004576:Electromyography / Q000295:instrumentation / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D012737:Sex Factors; D012815:Signal Processing, Computer-Assisted; D013703:Temporal Muscle / Q000502:physiology*; D013997:Time Factors