Background: Retraction of the posterior tongue facilitates bolus formation, food transfer and Stage II transport in chewing and swallowing. Surface electromyography of the neck region (N-EMG) enabled the evaluation of muscle function at the posterior tongue. Although previous studies showed that food hardness increased masticatory muscles EMG activity and volitional chewing altered swallowing, the effect of food properties and chewing condition on N-EMG activity has not yet been elucidated. Objective: To investigate the effect of food properties and chewing conditions on N-EMG. Methods: Twelve healthy adults (six men and six women, mean age 28.1 ± 2.7) participated in this study. Three test foods were used: a cookie (solid food), crushed cookies adjusted using agar and water (semisolid food) and crushed cookies adjusted using thickening agent and water (soft food). Masseter and submental muscle EMG and N-EMG activity were recorded while chewing the three test foods. Participants were instructed to masticate the three test foods in three chewing conditions: (a) chewing freely, (b) chewing test foods with the same number of chewing cycles as when chewing solid food and (c) chewing with a maximum effort. Results: Total N-EMG activity when chewing solid food was higher than that in the other two test foods regardless of the chewing condition. In soft food and semisolid food, the total N-EMG activity was increased by increasing the number of chewing cycles. Conclusion: The total N-EMG activity was increased while chewing hard food, which indicates the positive effect of chewing hard food on rehabilitation at the posterior tongue.
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