Carbohydrate Mouth Rinsing in Thermoneutral Enhances Prolonged Running Performance Compared to Hot-Humid Environment

Rinsing with carbohydrate (CHO) has been shown to provided ergogenic benefits on exercise performance of duration up to 1 h. However, the effect of CHO mouth rinsing within varying environmental conditions remains indistinct. The objective of the study was to investigate the effect of CHO mouth rinsing the effects of CHO mouth rinse on time to exhaustion (TTE) running performance in thermoneutral (TN) and hot-humid (HH) environment. Twelve well- trained male endurance runners (mean ± SD; age: 25 ± 3 years; body fat: 7.8 ± 1.8%; VO2peak: 59.8 ± 4.0 mL kg−1 min−1) performed steady-state running exercise at speed eliciting 70% of VO2peak until exhaustion. In a double-blind, randomised cross over design, two of the trials were conducted in a TN (20 ℃, 40% RH) with another two in a HH (30 ℃, 70% RH) environment. Each of the runners rinsed their mouth with either a 6% CHO solution, or a taste matched placebo (PLA) solution intermittently during exercise. A significant main effect of environment (TN vs. HH; p 0.05). There was no difference between plasma glucose or lactate between trials (p > 0.05). These data demonstrated that distinct influence of the environmental condition on the efficacy of CHO mouth rinsing and endurance running exercise performance. The increased in cardiovascular and physiological strain during the exhaustive running exercise observed in a heat environment were the key reasons for decreased exercise performance when compared to a cooler environment.