2.2. Experimental Design, Exercise Protocol, and Beverage Treatments
dehydration
DEHYDRATION
A randomized counter-balanced crossover design with double blinding was used. Each of the three trials occurred at least 3 days apart. During the 24 h period prior to each 8 h experiment, participants ate the exact same diet and did not exercise. To ensure a standardized diet with consistent energy and sodium intake, participants were provided with identical foods for meals during the 24 h period and surveyed for physical activity and diet to confirm consistency of conditions prior to each experiment.A diagram of the protocol is presented in To induce dehydration, participants exercised during a ~90 min session composed of three 25 min periods of intermittent-intensity exercise performed indoors after a 2 min warm-up. Exercise occurred on a treadmill, stationary bike, and elliptical machine; the order of use of the exercise machines varied between participants but was the same for an individual for all trials. Each 25 min period consisted of a fixed number of intervals at paces of walking (~3 mph), jogging (~7 mph), and running (10 mph), or the equivalent perceived intensities on the bike or elliptical machine (During data collection on the final six participants, a pilot study was conducted to explore the role of sodium balance on the completeness of rehydration. Sweat samples were obtained during the second 25 min period of exercise, after sweating was well established, and analyzed for sodium concentration to estimate whole-body sodium loss during exercise. The collection technique has been used in prior rehydration studies [During the exercise-dehydration period, no fluids were given to elicit a 2.5–3% reduction in body mass. Environmental conditions ranged from 22 to 29 °C (71 to 85 °F) and from 13 to 43% relative humidity. Following exercise completion, participants were weighed and rested for 45 min before consuming a volume of the beverage that replaced 100% of body mass lost. Beverages were ingested in six aliquots over a 1 h period given at the end of the trial. Specifically, 25% of the total volume was ingested every 10 min for the first 20 min; thereafter, 12.5% of the volume was ingested at four 10 min intervals.The composition of the beverages is presented in Each participant ingested a water placebo (with flavored powder, private label version of Crystal Lite