Coordinated electromyographic activity of the human masseter and temporalis anterior muscles during mastication

The present report aimed at evaluating the within- and between-subject electromyographic coordination between the masseter (M) and temporalis anterior (T) muscles during the performance of a standardized chewing task. Electromyographic activity of M and T muscles was recorded in 60 young healthy adults (30 men, 30 women) during two 15-s unilateral mastications of gum. Left-right differential potentials (delta M = MR-ML, delta T = TR-TL) were computed and the square root of (delta M2 + delta T2) moduli were calculated. The maximum modulus relative to each masticatory cycle was located, and each modulus and differential potential were expressed as a % of the maximum modulus for each subject and chewing trial. For each subject and chewing side, the masticatory frequency was computed, and statistics of the moduli as %s of the maximum were determined by means of bivariate analysis. Within-subject repeatability of the unilateral chewing patterns was good. Mean population values for the modulus position (bivariate analysis), chewing frequency, and maximum modulus of the differential potentials (univariate statistics) were computed. A significant gender difference was found for the masticatory frequency, with larger values in men than in women. Conversely, no gender or side differences were found for the mean values of the maximum modulus or for the mean position of the percentage moduli. The chewing test applied allowed the evaluation of the neuromuscular coordination during the performance of a standardized physiologic activity. In particular, it quantified the within-subject and chewing side repeatability of the muscular pattern.