Eight male runners performed four 2-hr treadmill runs at 65% ~ 0 , m a x in the heat (35"C, 15-20% RH). A different beverage was offered each trial and subjects drank ad libitum for 2 min every 20 min. The beverages were, 6% carbohydrate (CHO) solution (NC 6), 6% carbonated-CHO solution (C 6), 10% CHO solution (NC 10), and 10% carbonated-CHO solution (C 10). NC 6 and C 6 contained 4% sucrose and 2% glucose. NC 10 and C 10 contained high fructose corn syrup. Subjects drank more NC 6 than C 6. Fluid consumption was not different among other trials. During all trials, volume consumed and %ΔPV declined while heart rate and rectal temperature increased (p<0.05). No significant differences occurred between beverages for these variables. Percent body weight lost was greater (p<0.05) for the C 10 trial compared to the NC 6 trial. Neither sweat rate, percent fluid replaced, plasma [Na+], [K+], osmolality, percent of drink volume emptied from the stomach, or glucose concentration differed among trials. Plasma [K+] and osmolality increased (p<0.05) over time. Ratings of fullness and thirst were not different among beverages, although both perceptions increased (p<0.05) with time. It is concluded that (a) carbonation decreased the consumption of the 6% CHO beverage; (b) fluid homeostasis and thermoregulation were unaffected by the solutions ingested; and (c) fluid consumption decreased with time, while ratings of fullness and thirst increased.
The authors are with the Departments of Exercise Science, Psychology, and Pharmacology at The University of Iowa. Request reprints from Carl V. Gisolfi, Dept. of Exercise Science, N414 Field House, University of Iowa, Iowa City, IA 52242.