4. Discussion
bloating, thirst, flatulence, diarrhea, abdominal pain, stools/diarrhea, mean ≤, vomiting, nausea, Thirst, dehydration, headache
DEHYDRATION, HEAT
The most important finding of this exploratory study was that voluntary fluid intake with lactose-free skim milk was enough to maintain euhydration during 90 min of cycling exercise at 60–75% HRmax (mean RPE = 11.8) in the heat (32 °C, 70% RH). Net Fluid Balance was maintained both with milk and with water intake, while heat stress was enough to reduce NFB by 0.937 kg in the ND condition. Similarly, dehydration was statistically not different from zero for both SM and W (Voluntary fluid intake is influenced by a number of physiological, environmental, and psychological factors, including fluid palatability and beverage temperature [Urine output has been shown to be higher when drinking water [Under this particular protocol, voluntary fluid intake was enough to maintain euhydration during exercise. Previous studies have shown conflicting results. In a simulated 16 km outdoor race at 20.5 °C and 64% RH, Passe, et al. [This exploratory study evaluated a wide variety of GI symptoms which were expected to be lower than previously reported for various drinks, because of the utilization of lactose-free, skimmed milk. Lactose intake causes symptoms of bloating, flatulence, abdominal pain, and diarrhea in a large segment of the population [Under the study conditions, namely, 90 min of pedaling at moderate to high intensity in humid heat while drinking water or milk ad libitum, or ND, there were no reports of vomiting, nausea, loose stools/diarrhea, or headache. A majority of symptoms were very mild and not different among conditions (see The exercise protocol in the present study was enough, however, to produce significant differences among conditions in five GI symptoms (Both abdominal pain (mean ≤ 0.63) and belching (mean ≤ 1.19) scores were low but significantly higher for milk than for the other two conditions. It might be speculated that this obeys the slower gastric emptying and intestinal absorption of milk, apparent in the study by Shirreffs, Watson, and Maughan [Finally, we evaluated thirst, which is not really a GI symptom but is a very relevant perception during exercise. Thirst was higher when the subjects were not allowed to drink than when they drank water or milk ad libitum. This result conforms to logic, but also to experiments where thirst has been shown to be a good indicator of fluid needs in the absence of drinking [An important comment must be made regarding the exercise protocol. In this study, the exercise mode and intensity were selected as a means to induce dehydration; they should be the same for all three conditions. Intensity is hereby reported in terms of heart rate and ratings of perceived exertion, but no absolute measure of workload is provided. This should not be a problem as far as individual differences go; while not all participants might have exercised at the same relative intensity, the important issue is that the intensity was not different among conditions, as can be verified in 