This study aimed to describe the electromyographic (EMG) activity patterns of the genioglossus (GG) and suprahyoid (SHy) muscles during swallowing. The effects of changes in food texture/consistency and head posture on transport of the swallowed bolus were also investigated. Participants were 10 normal adults. Test foods consisted of a liquid, a syrup, or 4 ml of paste made from 0.5% or 1.0% agar. Each food was swallowed with the head in one of three positions, and EMGs and videofluorographic (VF) images were recorded. Mean values of onset, peak, and offset times, peak amplitude, area, and duration of the EMG burst were measured. The total swallowing time, oral ejection time, pharyngeal transit time, clearance time, fauces transit time, and upper esophageal sphincter (UES) transit time were measured. The GG muscle burst patterns showed two peaks (GG1 and GG2) during each swallowing. The offset time and duration of the GG1 burst and the onset, peak, and offset times and duration of both the GG2 and SHy bursts were significantly affected by food texture. There were no significant differences in bolus transit time among the different experimental conditions. Regression analyses demonstrated significant linear relationships between the tongue tip touching the palate and the peak of the GG1 burst, between passage of the bolus tail at the fauces and offset of the GG1 burst, between passage of the bolus tail at the UES and peak of the GG2 burst, and between passage of the bolus tail at the UES and offset of the SHy burst. These results demonstrate that the duration, but not the amplitude, of tongue and suprahyoid muscle activity were increased with increasing hardness of food during swallowing and that the bolus transit time can be fixed within a certain range of physical food properties.
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