Electromyographic evidence of local muscle fatigue in a subgroup of patients with myogenous craniomandibular disorders

Abstract

Ten female patients with myogenous craniomandibular disorders who had complete dentitions and mainly unilateral muscle pain and tenderness to palpation, and 10 healthy female controls, participated in the study. The surface electromyographic signals of masseter and anterior temporal muscles were recorded during 30-s test contractions at 50% of the maximum voluntary clenching effort. A force transducer placed between the central incisors recorded the maximum voluntary bite force. The patients exerted a lower maximum voluntary bite force than the controls ( p < 0.05). In the patients the electromyographic signals of the painful muscles were weaker than those of the painless muscles ( p < 0.01). The signals of the control subjects were stronger than those of the painless muscles of the patients ( p < 0.01). The mean power frequency of the signals, recorded at the start of the 30-s contractions, showed no differences between the painful and painless muscles and between the muscles of the patients and of the controls. The rate of mean power frequency shift in the electromyographic signal, as a response to the 30-s test contraction, was normalized with respect to the amplitude of that signal to account for its amplitude dependency. The painful muscles showed a higher normalized rate of mean power frequency shift than the painless muscles and the muscles of the control subjects ( p < 0.01). These results confirm the presence of an impaired condition in the painful muscles of this group of patients with myogenous craniomandibular disorders.