Carbohydrate ingestion during exercise

MASON, W. L., G. McCONELL, and M. HARGREAVES. Carbohydrate ingestion during exercise: liquid vs solid feedings. Med. Sci. Sports Exerc., Vol. 25, No. 8, pp. 966–969, 1993. Six trained men were studied during 2 h of exercise at 65% ·VO2max to examine the influence of the physical form of carbohydrate supplementation on blood glucose and insulin responses. Three exercise tests were performed in randomized order, at least 1 wk apart. Subjects ingested 25 g of carbohydrate or 500 ml of a sweet placebo (CON) at 0, 30, 60, and 90 min of exercise. Carbohydrate was ingested as 500 ml of a 5% rice-based liquid (L-CHO) or as a 31-g food bar (S-CHO). No differences in oxygen uptake, respiratory exchange ratio, or heart rate were observed between trials. Blood glucose levels were higher (P < 0.05) throughout exercise when carbohydrate was ingested, compared with CON. No differences in blood glucose during exercise were observed between L-CHO and S-CHO. Plasma insulin levels were higher (P < 0.05) after 120 min of exercise when carbohydrate was ingested. The results of this study indicate that carbohydrate supplements with differing physical form (liquid vs solid) but equal carbohydrate content produce similar blood glucose and insulin responses during exercise.