Repeatability of measurements of surface electromyographic variables during maximum voluntary contraction of temporalis and masseter muscles in normal adults.

This study evaluated the intraexaminer repeatability of measurements of surface electromyography (EMG) variables and functional indices of the myoelectric signals from the masseter and temporalis muscles bilaterally in 15 healthy men. The test was repeated on two different days without templates. The resting muscle activity was recorded once, and two kinds of maximum voluntary contraction (MVC) tasks were performed and recorded three times. The two MVC tasks involved clenching the teeth and biting down on two cotton rolls bilaterally with the posterior teeth. The intraclass correlation coefficient (ICC) of amplitude was >88% and that of frequency was >95% during the two MVC tasks but not under resting conditions. The ICC of the asymmetry and activity indices during the two MVC tasks was >76%. A Bland-Altman analysis revealed no significant difference in amplitude or frequency or in the two indices between the two days during the MVC tasks. In conclusion, the measurements of surface EMG variables and the indices obtained according to the study protocol were highly repeatable in healthy men. Additional studies using templates and intraexaminer measurement errors are warranted in both men and women for complete validation of these findings.