Tongue Strength Training Increases Daytime Upper Airway Stability in Rats

PURPOSE: Tongue strength training (TST) has been shown to decrease the apnea-hypopnea index in some patients with obstructive sleep apnea (OSA). However, whether TST modulates the central regulation of genioglossus and influences the stability of the upper airway remains unknown. The purpose of this study was to dynamically assess the effect of TST on the upper airway. METHODS: Sixteen adult male Sprague–Dawley rats were studied to explore the mechanism of TST improving the upper airway function. The rats were randomly assigned to the normal control (NC) and TST groups. The TST group underwent 8-week progressive resistance tongue exercise training. Transcranial magnetic stimulation (TMS) responses and EMG activities were consistently recorded for 2 h on days 0, 14, 28, and 56 of the experiments in both groups. Theoretical critical pressure (Pcrit) value was measured on days 0, 14, 28, and 56. RESULTS: The TST group showed shorter TMS latency and higher genioglossus EMG activity, which lasted from 5 min to 80 min after training on day 56 of training, than the NC group. The TST group showed significantly lower theoretical Pcrit values on days 28 and 56 of training than the NC group (-4.07±0.92 vs -3.12±0.77 cmH(2)O, P< 0.05, -4.66±0.74 vs -3.07±0.38 cmH(2)O, P< 0.01). CONCLUSION: This study revealed that an 8-week TST could gradually and transiently increase corticomotor excitability of genioglossus, elevate the genioglossus EMG activity, and ultimately enhance the stability of the upper airway during daytime. Moreover, improved neuromuscular excitability occurred prior to the enhanced upper airway stability. These findings provide a theoretical foundation for TST as a promising treatment for OSA patients.