2021 Volume 25 Issue 3 Pages 222-228
Purpose: The purpose of this study was to clarify the relationship between the amount of muscle activity in the jaw and hyoid muscles, the amount of muscle activity in the mylohyoid muscle while in the sitting position, and difficulty in swallowing.
Method: The subjects were 10 healthy adults. First, we measured muscle activity during posture maintenance. Then, we asked the subjects to perform the task of swallowing in nine postural patterns to identify difficulty in swallowing. Nine sitting posture patterns were set, which were a combination of three neck patterns―flexion at 20°, neutral position, and extension at 20°―and trunk inclination at 80°, 70°, and 60°. Difficulty in swallowing was evaluated and rated on a scale of 0 to 10, with 10 indicating the easiest swallowing, equivalent to that of the resting sitting position. Muscle activity was measured for the jaw, hyoid, and mylohyoid muscles.
Results: The degree of dysphagia was significantly lower when trunk inclination was at 60° than when flexion was at 20°, in the intermediate position, and extension was at 20°. When trunk inclination was at 60° and neck extension was at 20°, the value of swallowing difficulty was lowest compared to the other postures. In addition, a negative correlation was observed between the activity of the jaw and hyoid muscles and the mylohyoid muscle in subjects while in the sitting posture in a reclining wheelchair. Further, the integrated electromyography value while in the sitting posture in a reclining wheelchair was weakly correlated with difficulty in swallowing. The correlation coefficient ( r ) of the jaw and hyoid muscles was r = －0.50, and that of the mylohyoid muscle was r = －0.54.
Conclusion: When trunk inclination is at 60° and neck extension is at 20°, the value of swallowing difficulty is low compared to other postures because the mylohyoid and sternohyoid muscles are mobilized during posture maintenance. It was shown that the relationship between the amount of muscle activity in the jaw and hyoid muscles, the amount of muscle activity in the mylohyoid muscle while in the sitting position, and difficulty in swallowing was involved because a negative correlation was observed between the activity of the jaw and hyoid muscles and the mylohyoid muscle in subjects while in the sitting posture in a reclining wheelchair. In order to avoid dysphagia, positioning with less muscle activity in the mylohyoid and sternohyoid muscles should be observed.
