BETHESDA, Md. (Sept. 4, 2005) For over 20 years, the U.S. Army Research Institute of Environmental Medicine has studied the effect of temperature and the environment on physical performance. According to Michael Sawka, chief of USARIEM's Thermal and Mountain Medicine Division, "we're filling in the data gaps regarding the interaction of temperature and hydration on physical performance so we can set guidelines to optimize results relevant not just to soldiers or navy divers, but to athletes, firefighters and hunters anyone who's in extreme environments without access to food or water for long periods."
Several recent USARIEM studies in the Journal of Applied Physiology describe experiments in both warm and cold temperatures. One report showed that dehydration reduces physical performance, in this case cycling, 8% in temperate/cool air (68 degrees Fahrenheit), but only 3% in a cold 36 degrees F. Furthermore it found that cold weather itself had an insignificant impact on physical performance, irrespective of hydration level.
A second USARIEM-generated study found that ingesting glycerol, a sweetish syrup, was an effective hyperhydration agent, causing "nearly twice as much fluid" to be retained after four hours of cold-air exposure (CAE) compared with water ingestion alone. "This study also demonstrates that hyperhydration doesn't modify cardiovascular or thermoregulatory responses during resting CAE," the reported added.
How glycerol may hold water 'in reserve' in body for use later
The implications of the second study are particularly interesting for prolonged outdoor exposure when rehydration is not possible. "Because glycerol is freely distributed in body water, hyperhydration with GI (glycerol ingesti