A Preliminary Evaluation of Electromyographic Activities of Masseter Muscles during Speech in Myalgia Patients

Purpose: To evaluate the electromyographic activities (EMG) of masseter muscles during speech as a method for evaluating muscle fatigue in myalgia patients.Methods: The control group consisted of 6 subjects (3 males and 3 females, mean age 25.8 yrs), and the patient group consisted of 6 myalgia patients (6 females, mean age 29.5 yrs). The bilateral EMG of the masseter muscles were recorded using bipolar surface electrodes and a computer-based EMG analyzer (UAS-108, UNIQUE MEDICAL Co. Ltd.) during the following sessions: rest (30 seconds) / speech / rest (30 seconds) / maximum voluntary contraction (MVC, 5 seconds). Integrated electromyograms (IEMGs) and mean power frequency (MPF) were subjected to statistical comparisons between the two groups with t-test and Pearson’s product moment correlation coefficient.Results: No significant difference was found in the IEMG during speech between the two groups, while the myalgia patient group showed significantly lower IEMG than the control group during maximum voluntary contraction (MVC) (P=.004). MPF during speech was significantly higher in myalgia patients (P=.040). The same tendency was observed in MPF during MVC, although the difference was not significant. In the control group, strong correlations were found between MPFs during MVC and speech (r=.929, P=.007), and between IEMGs during MVC and speech (r=.822, P=.045). In myalgia patients, no such correlations were observed.Conclusion: The results from this study may suggest the possibility that MPF during speech can be a method for evaluating masticatory muscle fatigue.