Abstract: BACKGROUND: Modification of food consistency and volume is a commonly used method of swallowing compensation in clinical practice. Dry swallowing is a commonly used method of evaluation. The hyoid muscles are very important in swallowing. The effects of dry swallowing and swallowing tasks of different consistencies and volumes on hyoid muscle activation levels are still unclear.
OBJECTIVE: To explore the effects of simple dry swallowing and swallowing tasks of different consistencies and volumes on the hyoid muscles in healthy adults.
METHODS: A total of 44 healthy adults were included from April to August 2019, including 19 males and 25 females, with an average age of (21.7±2.8) years. They randomly performed dry swallowing and swallowing tasks of different consistencies (the International Dysphagia Diet Standardisation Initiative (IDDSI) frame levels 0-4) and volumes (5, 10, 20 mL), and the surface electromyogram signals of the hyoid muscles during each swallowing task were recorded. After processing the raw surface electromyogram signals, the activation levels of the hyoid muscles were compared between dry swallowing and swallowing tasks of different consistency and volume.
RESULTS AND CONCLUSION: The mean amplitude values of the suprahyoid muscles corresponding to swallowing tasks of 20 mL for levels 0-4, 10 mL for level 3, and 5 mL for level 4 were higher than those of dry swallowing (P < 0.05). The mean amplitude values of the suprahyoid muscles corresponding to the 20-mL swallowing tasks of different consistencies were higher than those of the 5-mL swallowing tasks of the corresponding consistencies, except for level 3 (P < 0.05). The mean amplitude values of the suprahyoid muscles corresponding to the 20-mL swallowing tasks of different consistencies were higher than those of the 10-mL swallowing tasks of the corresponding consistencies, except for levels 2 and 3 (P < 0.05). The mean amplitude values of the infrahyoid muscles corresponding to all swallowing tasks were higher than that of dry swallowing (P < 0.05). The mean amplitude values of the infrahyoid muscles corresponding to the 20-mL swallowing tasks of different consistencies were higher than that of the 5- and 10-mL swallowing tasks of the corresponding consistencies (P < 0.05). The mean amplitude values of the infrahyoid muscles corresponding to the 10-mL swallowing tasks of different consistencies were higher than those of the 5-mL swallowing tasks of the corresponding consistencies, except for level 3 (P < 0.05). To conclude, in healthy adults performing swallowing tasks of different volumes and consistencies, the level of activation of the hyoid muscles is less susceptible to IDDSI frame levels 0-4 consistency and more susceptible to volume. The higher volume indicates the higher activation level of the hyoid muscles.

Key words: swallow, dry swallowing, surface electromyography, hyoid muscles, suprahyoid muscles, infrahyoid muscles, consistency, volume