“While the common approach to managing health in hot environments centers around maintaining hydration, limited attention is devoted to managing heat production from hard work or play,” explained lead investigator Brent C. Ruby, PhD, FACSM, Director of the Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula. “It should be obvious that as the temperature rises, so does the body’s need for proper fluid intake patterns.
This ensures that blood and sweat volume can be maintained to continually enable heat loss through evaporative cooling (good old fashioned sweating). However, coaches, trainers, clinicians, medics, and safety officers continually emphasize the importance of proper hydration without providing sound guidance and attention to proper management of heat production from the working muscle.“
Typically, you should be avoiding 2% loss of body mass due to modest dehydration. The guidelines for minimum hydration is 2g of water per kilogram of body weight. And, while there is a guideline for volume of water, there is none for temperature of water. In this study, researchers decided to look into how water temperature impacts the body by subjecting participants to intense exercise in 88° F heat and 50% relative humidity for 3 hours.
“While these guidelines serve as just that, ‘guidelines,’ constant access to body weight scales for repeated measures of nude body weight is impractical for nearly all sport or occupational settings. Reducing the emphasis on fluid volume, allowing cold fluid access, and emphasizing the need to rest adequately during the training session or workshift should become common practice,” stated Dr. Ruby.
During the trial, participants were randomly given one of three treatments: ambient temperature water at a rate of 2g·kg-1 of body mass; ice slurry (2/3 shaved ice and 1/3 water) at a rate of 2g·kg-1 of body mass; or the ice slurry mixture, but at a reduced rate of 1g·kg-1 of body mass. Each 2g·kg-1 body weight drink was provided at 10-minute intervals.
Other physiological and thermoregulatory parameters were measured during the 3 hours. Researched discovered that the ice slurry mix, even at amounts that resulted in a 2% body mass loss, faired just as well as when subjects were provided the full amount of room temperature water.
“There were no differences in rectal temperature, heart rate, physiological strain index, skin temperature, sweat loss, or rating of perceived exertion during three hours of exercise in the heat when participants were provided half the volume of fluid in the form of the ice slurry in comparison to ambient temperature water,” said Dr. Ruby.
In addition, while the ice slurry mix was just as effective at a lower amount than regular temperature water, when given at a similar rate, there was a marked improvement in performance. Rectal and skin temperatures, heart rate, and overall all physiological strain were lower at the end of the exercise period, making the full amount of ice slurry the most effective solution.
“We want to emphasize that the temperature of fluids delivered will alter the physiological and thermoregulatory response during work in the heat. Consuming ambient temperature water did not improve the physiological or thermoregulatory responses compared to the one-half volume ice slurry/water mixture,” noted Dr. Ruby.
While it has been common knowledge, based on past research, that cold water is a more effective way to hydrate, this new information reveals that temperature may be as important as volume. So, if you are working out in very hot conditions you won’t need to carry or use as much water if it is cold. This has particular significance for military personnel and first responders working in hot environments for long periods of time. For these individuals having to carry a lot of fluid may be a hinderance.
Further research is needed, according to Dr. Ruby, to determine the impact of exchanging fluid temperature for fluid volume has on performance.