Effects of sour stimulus concentrations on surface electromyographic signals of swallowing muscle in healthy young adults

Objective This study aimed to analyze the alterations in swallowing muscle activity induced by sour stimulation of different concentrations. By collecting and processing surface electromyographic (sEMG) signals from the bilateral masseter (MAS), submental muscle group (SMC), and infrahyoid muscle group (IHM) in healthy individuals, we explored the modulatory effects of oral sour sensory stimulation on swallowing muscle activity. Methods Twenty-six healthy young adults (13 men, 13 women) participated. Test liquids were administered in a fixed sequence: room-temperature water, low-, medium-, and high-concentration sour water. Before each trial, participants rinsed with room-temperature water for 15 s and rested for 3 min. A gauze pad soaked with the test liquid was placed on the central tongue. Participants kept their mouths closed, with the tongue maintained in light contact with the hard palate for 5 s. Bilateral sEMG signals of the target swallowing muscles were synchronously recorded, and the core indicators, including root mean square (RMS) and mean power frequency (MPF), were extracted for subsequent quantitative analysis. Results RMS showed a significant main effect of concentration ( F (3, 1211.07) = 9.31, p < 0.001) and a significant concentration × muscle interaction ( F (6, 1211.07) = 2.28, p = 0.034). Bonferroni-adjusted comparisons showed higher RMS under the high-concentration condition than under room-temperature water and the low-concentration condition in the MAS ( p = 0.001; p < 0.001) and SMC ( p = 0.012; p = 0.008). MPF showed neither a significant concentration effect ( p = 0.927) nor a significant concentration × muscle interaction ( p = 0.937). Conclusion High-concentration sour stimulation was associated with higher sEMG RMS in the MAS and SMC in healthy young adults. Concentration-related RMS responses varied across muscle groups, whereas no concentration-related change in MPF was detected. The functional significance of these electrophysiological findings requires further investigation using objective swallowing assessments.