Effect of dilute CHO beverages on performance in cool and warm environments

Purpose: This evaluated the efficacy of drinks containing low concentrations of carbohydrate (CHO; 2-6%) on physical performance in cool and warm environments. Methods: In two separate, but related studies, 24 healthy males completed a familiarisation trial and four trials to volitional exhaustion (TTE) at 70% VO2max in cool conditions (10C, n = 12) or 60% VO2max in a warm environment (30C, n = 12). Subjects ingested 0%, 2%, 4% or 6% CHO solutions (sucrose, glucose and fructose in a ratio of 50:25:25) immediately before exercise and every 10 minutes during exercise. Results: TTE in 10C was 102.6 ± 33.9 minutes, 109.2 ± 33.9 minutes, 121.0 ± 25.7 minutes and 122.4 ± 29.9 minutes in the 0%, 2%, 4% and 6% trials respectively (P = 0.012). Compared to the 0% trial, TTE was longer on the 4% (P = 0.032; ES 0.72) and 6% (P = 0.044; ES 0.66) trials. In addition, TTE was longer on the 6% trial than the 2% trial (P = 0.025). TTE was also significantly influenced by drink CHO content at 30C (0% 94.5 ± 24.5 minutes, 2% 104.1 ± 20.1 minutes, 4% 105.5 ± 26.7 minutes, 6% 112.0 ± 28.7 minutes; P = 0.046). No differences in TTE were apparent between 0% and the 2% or 4% trials, but TTE was longer on the 6% compared to the placebo (P = 0.045; ES 0.62). Heart rate, core temperature or rates of substrate oxidation were not affected by drink CHO content. Conclusions: These results demonstrate significant improvements in exercise capacity over the placebo trial when 4% and 6% CHO solutions were ingested at 10C and a 6% CHO drink at 30C.