Related Experiment Videos
Fluid replacement during sustained activity in the heat: nutrient solution vs. water.
L Levine1, M S Rose, P Francesconi
1U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760-5007.
Aviation, Space, and Environmental Medicine
|June 1, 1991
Summary
Consuming a nutrient solution or flavored water during prolonged exercise in heat showed similar hydration and thermoregulation benefits. Both options supported sustained activity without significant physiological differences over 13 hours.
Area of Science:
- Exercise Physiology
- Environmental Physiology
- Human Performance
Background:
- Sustained physical activity in hot environments poses significant thermoregulatory and hydration challenges.
- Nutrient solutions are often considered for prolonged exercise, but their benefits compared to simple hydration are debated.
Purpose of the Study:
- To compare the thermoregulatory and hydrational effects of a nutrient solution versus flavored water during sustained exercise in a hot-dry environment.
- To assess the impact of these beverages on physiological markers and gastric emptying rates.
Main Methods:
- Eleven heat-acclimated men performed 13-hour sustained activity trials (alternating walking and rest) in a hot-dry environment (37°C, 20% RH).
- Physiological parameters including core/skin temperature, sweating rate, and plasma markers were monitored.
- Gastric emptying rates were measured in a separate experiment with nine participants during exercise (55% VO2max) in heat (35°C, 20% RH).
Main Results:
- No significant differences were found between the nutrient solution and water for metabolic rate, fluid intake, temperature, or sweating rate over 13 hours.
- Plasma osmolality increased by hour 8, and plasma free fatty acids decreased by hour 11 in the nutrient trial compared to the control.
- Gastric emptying rates for both the nutrient solution and water were similar (approximately 20 ml/min) during exercise in the heat.
Conclusions:
- Both nutrient solution and flavored water provide comparable thermoregulatory and hydrational benefits during 13 hours of sustained activity in a hot environment.
- The similar gastric emptying rates suggest that fluid absorption and physiological responses are not significantly different between the two beverage types under these conditions.
- These findings support the use of simple hydration or nutrient solutions for maintaining physiological balance during prolonged heat exposure and exercise.