This study aimed to determine whether the pattern of carbohydrate sports drink ingestion during prolonged submaximal running affects exogenous carbohydrate oxidation rates and gastrointestinal (GI) comfort.
Twelve well-trained male runners (27 ± 7 yr; 67.9 ± 6.7 kg; V˙O2peak, 68 ± 7 mL·kg−1·min−1) completed two exercise trials of 100 min steady-state running at 70%V˙O2peak. In each of the trials, 1 L of a 10% dextrose solution, enriched with [U-13C] glucose, was consumed as either 200 mL every 20 min (CHO-20) or 50 mL every 5 min (CHO-5). Expired breath and venous blood samples were collected at rest and every 20 min during exercise. Subjective scales of GI comfort were recorded at regular intervals.
Average exogenous carbohydrate oxidation rates were 23% higher during exercise in CHO-20 (0.38 ± 0.11 vs 0.31 ± 0.11 g·min−1; P = 0.017). Peak exogenous carbohydrate oxidation was also higher in CHO-20 (0.68 ± 0.14 g·min−1 vs 0.61 ± 0.14 g·min−1; P = 0.004). During exercise, total carbohydrate oxidation (CHO-20, 2.15 ± 0.47; CHO-5, 2.23 ± 0.45 g·min−1, P = 0.412) and endogenous carbohydrate oxidation (CHO-20, 1.78 ± 0.45; CHO-5, 1.92 ± 0.40 g·min−1; P = 0.148) were not different between trials. Average serum glucose (P = 0.952) and insulin (P = 0.373) concentrations were not different between trials. There were no differences in reported symptoms of GI comfort and stomach bloatedness (P > 0.05), with only 3% of reported scores classed as severe (≥5 out of 10).
Ingestion of a larger volume of carbohydrate solution at less frequent intervals during prolonged submaximal running increased exogenous carbohydrate oxidation rates. Neither drinking pattern resulted in increased markers of GI discomfort to a severe level.