Effect of a carbohydrate-electrolyte drink on endurance capacity during prolonged intermittent high intensity running

Objective - To examine the effect of a carbohydrate-electrolyte solution on endurance capacity during prolonged intermittent running. Methods - Nine subjects (eight men and one woman) ran to exhaustion on a motorised treadmill on two occasions separated by at least 10 days. After an overnight fast, they performed repeated 15 second bouts of fast running (at 80% Vo₂MAX for the first 60 minutes, at 85% Vo₂MAX from 60 to 100 minutes of exercise, and finally at 90% Vo₂MAX from 100 minutes of exercise until exhaustion), separated by 10 seconds of slow running (at 45% Vo₂MAX). On each occasion they drank either a water placebo (P) or a 6.9% carbohydrate-electrolyte (CHO) solution immediately before the run (3 ml/kg body mass) and every 20 minutes thereafter (2 ml/kg body mass). Results - Performance times were not different between the two trials (112.5 (23.3) and 110.2 (21.4) min for the P and CHO trials respectively; mean (SD)). Blood glucose concentration was higher in the CHO trial only at 40 minutes of exercise (4.5 (0.6) v 3.9 (0.3) mmol/l for the CHO and P trials respectively; p < 0.05), but there was no difference in the total carbohydrate oxidation rates between trials. Conclusion - These results suggest that drinking a 6.9% carbohydrate-electrolyte solution during repeated bouts of submaximal intermittent high intensity running does not delay the onset of fatigue.