The Association Between Intramuscular Characteristics of Swallowing-Related Muscles and Oral Function: A Study in Older Women Living in the Community

Background: Muscle quality, along with muscle mass, deteriorates with disuse, ageing and various disorders, underscoring the need to evaluate the internal characteristics of swallowing-related muscles. Previous studies have reported an association between oral function and echo intensity (EI), but the association between oral function and the stiffness of swallowing-related muscles, as well as the degree of this association, remains insufficiently understood. Objective: To examine the association between oral function and the intramuscular characteristics of swallowing-related muscles, focusing on muscle stiffness. Materials and Methods: A total of 196 older women (78.1 ± 5.2 years) participated in a physical fitness measurement session in this cross-sectional study. The stiffness and EI of the geniohyoid muscle (GHM) were measured, and oral function was evaluated using oral diadochokinesis (ODK; /pa/, /ta/, /ka/) and tongue pressure. Multiple regression analysis was used to investigate the association between oral function, stiffness and EI. By standardising the variables, we evaluated these associations independently of the units. Results: ODK, /pa/ (β = −0.144, p = 0.002), /ta/ (β = −0.134, p = 0.011) and /ka/ (β = −0.093, p = 0.043) showed a negative association with GHM stiffness. After standardisation, the association between ODK (/pa/, /ta/, /ka/) and GHM stiffness (β: −0.144, −0.134, −0.093) was comparable to that between ODK and EI (β: −0.008, −0.148, −0.075). Conclusion: GHM stiffness was associated with oral motor function in older women living in the community. Assessing the stiffness of swallowing-related muscles could be important for evaluating oral function to a degree comparable to EI.