Electromyographic study of masticatory muscle fatigue and recovery under voluntary contraction. 2. Comparison between normal subjects and craniomandibular disorder patients

Abstract

During fatiguing clenching, power spectrum in the surface electromyogram decrease to the lower frequency. The phenomenon has been expected to indicate the fatiguing condition. However, the underlying mechanism between the muscle fatigue and the power spectrum shift is still unclear. Therefore, it may be difficult to employ the spectrum shift for the diagnostic process. The aim of this paper was to clarify the mechanism in the power spectrum shift and to find a possible parameter for diagnostic process. The shift in the mean power frequency (MPF) was observed during fatiguing clenching and the successive recovery period from a normal group (n = 47) and a craniomandibular disorder patient group (n = 46). The results suggested that the power spectrum shift during the fatiguing clenching might be due to a reflex inhibition at the motoneuron level. From the comparison between the normal group and the dysfunctional group, there was larger difference in normalized absolute MPF values between the right and left muscles. Also the larger variance was seen during the fatiguing process and the recovery process in the dysfunctional group than in the normal group.