FOOD PROPERTIES THAT INFLUENCE NEUROMUSCULAR ACTIVITY DURING HUMAN MASTICATION

The rate of breakdown of food in mastication depends on the ratio of t wo mechanical properties of the food-the toughness and modulus of elas ticity (Agrawal et al., 1997)-a result which can be predicted by an an alysis of the energetics of fracture. The work input to produce food f ragmentation is provided by the masticatory muscles, the activity leve ls of which depend on sensory feedback from the mouth. Here, we test t he hypothesis that the activity of a representative of this musculatur e is modulated by the above combination of food properties. The surfac e electrical activity (EMG) of the anterior temporalis muscles of ten human subjects was recorded while subjects chewed standardized volumes of 15 food types. The integrated EMG in these muscles was highly sign ificantly related to the square root of the ratio of the above two foo d properties. Significant correlations were found between this food pr operty index and integrated EMG, both when data for all chews and all subjects were lumped together (r = -0.86; p < 0.0001) and when correla tion coefficients between the index and EMG were plotted for each chew made by each subject. Except for two subjects in the first chew, thes e coefficients reached and maintained highly significant levels throug hout the masticatory sequence. Thus, a clear relationship between the electrical activity of a jaw-closing muscle and the mechanical propert ies of food has been found for the first time.