Watson, P., Shirreffs, S. M., & Maughan, R. J. (2012). Effect of dilute CHO beverages on performance in cool and warm environments. Medicine & Science in Sports & Exercise, 44, 336-343.

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This study evaluated the value of drinks containing low concentrations of carbohydrate (2%-6%) on physical performance in cool and warm environments. In two separate but related studies, healthy males (N = 24) completed a familiarization trial and four trials to volitional exhaustion at 70% VO2max in cool conditions (10C, N = 12) or 60% VO2max in a warm environment (30C, N = 12). Ss 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.

Time-trials to exhaustion in 10C were 102.6 33.9, 109.2 33.9, 121.0 25.7, and 122.4 29.9 minutes in the 0%, 2%, 4%, and 6% trials, respectively. Compared to the 0% trial, time-trial performance was longer in the 4% and 6% trials. Time-trial performance was longer in the 6% trial than in the 2% trial. Time-trial performance was also significantly influenced by drink CHO content at 30C (0% = 94.5 24.5 minutes, 2% = 104.1 20.1 minutes, 4% = 105.5 26.7 minutes, 6% = 112.0 28.7 minutes). There were no differences in time-trial performances between the 0% and the 2% or 4% trials. Time-trial performance was longer in the 6% trial compared with the placebo. Heart rate, core temperature, or rates of substrate oxidation were not affected by drink CHO content.

Implication. Exercise capacity is improved over no-CHO supplementation depending upon the temperature. At 10C, 4% and 6% CHO drinks are effective. With hotter temperatures (30C) a 6% drink is effective. The strength of advisable CHO supplementation drinks depends upon the ambient temperature in the sporting environment.

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