Evaluating the effect of trunk angle on the biomechanics of tongue, hyoid, and swallowing-related muscles during normal oropharyngeal swallowing with a non-invasive sensing system.

Body posture plays an important role in the normal oropharyngeal swallowing process. We aimed to clarify the effects of trunk angle on the biomechanics of the tongue, hyoid, and suprahyoid and infrahyoid muscles during normal oropharyngeal swallowing. For this purpose, fifteen healthy male participants (aged 27.7 ± 1.8 years) were recruited. They swallowed 15 ml of water in three random trunk angles (90°, 60°, 30°), and tongue pressure, hyoid bone movement, and the activity of the suprahyoid and infrahyoid muscles were monitored simultaneously by a non-invasive sensing system. Then, the temporal sequence as well as the parameters such as duration, peak value, and interval of the above-mentioned oropharyngeal structural motions were assessed. Results showed that the temporal sequence of tongue pressure, hyoid motion, and myoelectric activities during oropharyngeal swallowing was stable without any variation among the three postures. As the body gradually inclined, the onset and offset of the hyoid stationary phase and the offset of hyoid movement were delayed, and the hyoid elevation phase was prolonged (p < 0.05). No significant differences were detected for any of the parameters of tongue pressure (p > 0.05) except for tongue pressure duration at the anterior part (p < 0.05). In addition, no significant postural effects were observed for the duration, peak value, and electromyographic area of the suprahyoid muscle or infrahyoid muscle (p > 0.05). These findings suggest that trunk angle had no effect on the biomechanical sequence of the tongue, hyoid, and muscles during oropharyngeal swallowing in healthy adults, and the oropharyngeal structures will accommodate and finely regulate according to body posture.