Body cooling between two bouts of exercise in the heat enhances subsequent performance.

The purpose was to assess whether body cooling between 2 bouts of exercise in the heat enhances performance during the second exercise session. Using a random, crossover design, 15 subjects (3 women, 12 men; 28 +/- 2 years, 180 +/- 2 cm, 69 +/- 2.3 kg) participated in all 3 trials. Subjects ran 90 minutes on hilly trails in a hot environment (approximately 27 degrees C) before 12 minutes of either cold water immersion (CWI; 13.98 degrees C), ice water immersion (IWI; 5.23 degrees C), or a mock treatment (MT) of sitting in a tub with no water (29.50 degrees C). After immersion, subjects ran a 2-mile race. CWI had faster (p < 0.05) performance time (725 seconds) than MT (769 seconds). CWI and IWI had significantly (p < 0.05) lower rectal temperatures postimmersion than MT as well as postrace (p < 0.05). Heart rate also remained significantly lower (p < 0.05) during the CWI and IWI trials for the first half of the race. In conclusion, CWI enhances performance (6% improvement in race time) in the second bout of exercise, supporting its potential role as an ergogenic aid in athletic performance.

Influence of a Pre-Exercise Glycerol Hydration Beverage on Performance and Physiologic Function During Mountain-Bike Races in the Heat.

OBJECTIVE: To determine if pre-exercise hydration with and without glycerol differentially affects physiologic and performance responses during mountain-bike races in the heat. DESIGN AND SETTING: Testing (random, crossover, double-blind design) included the following 3 treatments administered in conjunction with a 30-mile mountain-bike race consisting of three 10-mile (16-km) loops: (1) no water during exercise (NE): water consumed before the race and no water consumed during the race, (2) glycerol (G): mixture of water and glycerol consumed before the race and water via 2 water bottles consumed during the race, and (3) water (W): water consumed before the race and water via 2 water bottles consumed during the race. Subjects stopped for 8 minutes after each 10-mile loop for collection of data. SUBJECTS: Twelve heat-acclimated male mountain bikers with age = 24.5 +/- 1.1 years, percentage of body fat = 14.3 +/- 1.0%, mass = 76.9 +/- 1.9 kg, height = 179 +/- 2 cm. MEASUREMENTS: We measured body weight, percentage of body fat, rectal temperature, blood lactate, blood glucose, urine volume, urine color, urine specific gravity, thirst sensation, thermal sensation, rating of perceived exertion, fluid consumption, heart rate, and sweat rate. Each subject completed the Environmental Symptoms Questionnaire. RESULTS: The G trial was less dehydrated than the NE and W trials postexercise. Pre-exercise urine volume was less in the G trial than in the NE and W trials, and postexercise thirst was less in the G trial than the NE and W trials. Postexercise Environmental Symptoms Questionnaire scores were lower in the G trial than the NE or W trials. It is noteworthy that, although not significant, the G trial performed 5 minutes faster on loop 3 than the NE and W trials. CONCLUSIONS: Lower Environmental Symptoms Questionnaire scores and percentage of dehydration may indicate decreased signs and symptoms of heat strain in the G trial. Based on the NE trial performance, adequate pre-exercise hydration, even without glycerol, may limit the detrimental effects of dehydration.