Differences in Tongue Muscle Activity During Chewing of Rice With Various Textures

Background The tongue performs finely coordinated movements during mastication in response to bolus properties; however, few studies have quantitatively evaluated tongue muscle activity during this process. Objective This study aimed to quantify tongue muscle activity during chewing of rice with different physical properties. Methods Ten healthy young adults chewed three types of rice‐based foods with different textures (regular, soft and extra soft) unilaterally on either the left or right side in random order. Electromyographic (EMG) activity of the tongue was recorded using suction surface electrodes, while activity of the masseter and suprahyoid muscles was recorded using conventional surface electrodes. The chewing sequence was divided into early, middle and late stages. Muscle activity per chewing cycle was analysed separately for the chewing and balancing sides. Bolus hardness, cohesiveness, adhesiveness and moisture content were also measured at different chewing stages. Results Bilateral masseter muscle activity was significantly greater for regular rice than for extra soft rice during the early and middle stages of chewing. In contrast, tongue muscle activity progressively increased towards the late stage during soft and extra soft rice intake and bilateral tongue muscle activity was significantly greater for extra soft rice than for regular rice in the late stage. Chewing cycle duration did not differ among food types, indicating that these differences reflected increased EMG amplitude per unit time. At the late stage of chewing, the extra soft bolus showed the lowest hardness but the highest cohesiveness and moisture content. Conclusion Tongue muscle activity varied according to both the chewing stage and bolus properties. In particular, tongue muscle activity increased during the late stage of chewing when softer, wetter and more cohesive boluses were processed, suggesting a role of tongue muscles in bolus gathering, shaping and transport towards the pharynx.