The amplitude distribution of electromyographic activity of masticatory muscles during unilateral chewing.

The amplitude probability distribution function (APDF) of electromyographic activity was used to describe the variation in relative masticatory force in the superficial masseter muscle and the anterior temporal muscle during unilateral chewing. The masticatory force, predicted from an isometric reference contraction, increased significantly in both muscles when chewing an almond compared to chewing half a stick of gum. Analysis of the distribution levels of contraction showed that the significant differences in relative masticatory forces were found for high levels of contraction. The individual variations were large when masticatory force between the muscles was compared. Maximal loading of the masseter muscle and the anterior temporal muscle exceeded 100% of the reference voluntary contraction in six females out of nine, mainly during chewing of an almond. The results indicated that APDF can be useful for analysing chewing when estimations of relative masticatory force and a measure of the distribution of different levels of contractions are desirable.