The Effect of Carbohydrate or Salt Mouth Rinse on Corticospinal Responsiveness Following a Fatiguing Isometric Contraction

Mouth rinsing with carbohydrates or salt solutions has been shown to attenuate the reduction in maximum voluntary contraction (MVC) strength during fatigue. Although central mechanisms, such as changes in voluntary activation (VA) and motor evoked potentials (MEP), have been proposed to explain this effect, direct evidence is limited. This study aimed to investigate the effects of carbohydrate or salt mouth rinses on central fatigue by examining whether central measures are affected. In a double-blind, randomized, crossover design, 19 male participants completed three experimental trials (carbohydrate, salt, or placebo mouth rinses), each involving a sustained knee isometric fatiguing protocol performed until volitional fatigue. MVC, VA, and MEP were assessed before and after the fatiguing protocol. Following the protocol, the torque output (MVC) and central measures (VA and MEP) showed significant reductions (p < .05). Although the reductions following carbohydrate and salt were less pronounced (MVC, VA, and MEP), both treatments showed better preservation than placebo (p < .001). In addition, the comparable reduction in resting twitch and maintenance of maximum compound muscle action potential (p > .05) suggest that the observed benefits were primarily central mediated. This is the first study to demonstrate that salt mouth rinsing is as effective as carbohydrate rinsing in attenuating neuromuscular fatigue via central mechanisms, preserving muscle activity, central drive, and corticospinal responsiveness following a localized fatiguing protocol.