The purpose of this study was to investigate the effects of different training methods for the suprahyoid muscles on the amount of muscle activity of the swallowing-related muscles in a training task utilizing jaw opening movements and head and neck flexion.

　Method:　Thirty-three healthy adults (20 males, 13 females; mean age 33.8±6.9 years) were included in the study. The method consisted of four types of training exercises: jaw opening exercise (JOE), resistive jaw opening exercise (RJOE), head lift exercise (HLE), and forehead exercise for suprahyoid muscles. The muscle activities of the suprahyoid and infrahyoid muscles, and sternocleidomastoid muscles were recorded with a surface electromyograph during the four training exercises. The 5-second period from the start to the end of each training task was used as the analysis interval, and the maximum and average amplitude values were calculated from the EMG of each muscle under test.

　Results:　The RJOE exhibited the highest maximum and mean amplitude values for the suprahyoid muscles, with no significant difference between the RJOE and the HLE, but there was a significant difference between the RJOE and the swallowing forehead exercises. HLE had the highest maximum and mean amplitude values for the suprahyoid muscles and sternocleidomastoid muscles, with significant differences between RJOE and JOE.

　Conclusions:　In training methods utilizing jaw opening exercises (JOE, RJOE), muscle activity of the suprahyoid muscles was high, while that of the infrahyoid muscles and sternocleidomastoid muscles were low. In training methods involving head and neck flexion (HLE, swallowing forehead exercises), not only the suprahyoid and infrahyoid muscles but also the sternocleidomastoid muscles were more active. Because the activities of the suprahyoid and infrahyoid muscles, and sternocleidomastoid muscles differ depending on the training method, effective swallowing rehabilitation can be provided by selecting or combining training methods that utilize jaw opening and head and neck flexion exercises, depending on the dysphagia status of the patient when strength training is performed on the swallowing-related muscles. This will enable the provision of effective swallowing rehabilitation.

　Introduction:　Surface electromyography (sEMG), a widely used noninvasive technique for assessing muscle activity, can be used to measure muscle activity during swallowing. However, the changes in the muscle activity of each swallowing-related muscle depend on the material swallowed and remain unclear. Therefore, we investigated the changes in muscle activity in the submandibular region using a seven-channel sEMG when swallowing different materials.

　Materials and Methods:　This study included 66 healthy volunteers (53 males; mean age, 37.3±13.9 years). A seven-channel sEMG was used to assess and record the submandibular muscle activity of each participant when swallowing saliva, 5 mL of water, and a capsule. The duration of muscle activity (ms), maximum amplitude (mV), and integrated muscle activity (mV・ms) during swallowing were calculated from the sEMG recordings. Statistical analysis was performed using JMP pro16. One-way analysis of variance was used to analyze the muscle activity for the different materials swallowed, and a t-test was performed to compare with muscle activities from each electrode. Bonferroni correction was performed and p-values ＜0.017 were considered statistically significant.

　Result:　No significant difference was observed in the duration of muscle activity among the different materials swallowed in any channel. Some channels indicated a significant difference in the maximum amplitude between the swallowed materials as follows: center-middle channel: saliva vs. water, and capsule vs. water. Moreover, some channels indicated a significant difference in the muscle activity between the swallowed materials as follows: right-front channel: capsule vs. saliva, and capsule vs. water, center-middle channel: capsule vs. water, center-rear channel: capsule vs. water.

　Conclusion:　The results of this study suggest that the muscle activity required was greater for solids than for water, and for saliva than for water, in the central part of the submandibular region during swallowing.