The effect of carbohydrate and salt oral stimulations on central fatigue

Rinsing the mouth with carbohydrate (CHO) or salt solutions can improve maximum voluntary contraction (MVC). While central involvement has been implicated with these mouth rinses (MRs), it remains unclear whether voluntary activation (VA) and central activation ratio (CAR) are affected. Thus, this study aimed to investigate these effects. Nineteen fasted male participants completed three trials of 30-minute cycling exercise. Using a randomised cross-over study design, participants rinsed with either a 6.4% maltodextrin solution, a 6.4% salt solution or a taste-matched placebo (PLA) for 10 seconds immediately before and every 10 minutes during exercise. Neurophysiological measures (VA, EMG, CAR) were recorded during MVC and sustained MVC (sMVC) before and after the cycling trials. Interestingly, MVC, sMVC and all neurophysiological measures showed significant interaction with group and time effects, where CHO and salt MRs outperformed PLA (p < 0.05). The findings imply that both MRs help sustain muscle contractions by preserving muscle activity and central drive. Notably, this is the first study to demonstrate that salt MR attenuates neuromuscular fatigue through central involvement, similar to CHO. This discovery opens opportunities for further investigations using specific measures, such as motor-evoked potential to substantiate central involvement.