Can the subject reliably reproduce maximum voluntary contraction of temporalis and masseter muscles in surface EMG?

OBJECTIVE: To evaluate the repeatability of the surface EMG variables of myoelectric signals from the masseter and temporalis muscles according to three methods to induce maximum voluntary contraction (MVC) in healthy adults. METHODS: Thirty healthy young subjects performed the following three MVC tasks three times each in three sessions on the same day without replacing surface electrodes: clenching the teeth (MVCIC) and biting down on two cotton rolls bilaterally with the posterior teeth (MVCBP) or first molars (MVCB6). RESULTS: The intra-class correlation coefficient (ICC) of the amplitudes during the three MVC tasks ranged from 65 to 79%. The ICCs of the spectral variables ranged from 78 to 86%. The ICCs of the asymmetry index of the masseter ranged from 77 to 86%, and those of the activity index ranged from 68 to 90%. CONCLUSION: The surface EMG measurements according to the three MVC methods exhibited good to excellent reproducibility.