Effects of three hydration beverages on exercise performance during 60 hours of heat exposure

Without adequate hydration, profound heat stress and dehydration can occur in people who work in hot environments. This study evaluated the effectiveness of three beverages on temperature regulation, cardiovascular response, and work performance during 60 h of dry heat exposure. Volunteer subjects lived in a climatic chamber in simulated desert conditions varying from 25-45 degrees C at 20% relative humidity. They performed three submaximal exercise sessions on a motorized treadmill at 4-h intervals each day. All of the subjects consumed one of three beverages: a water placebo, a 5% carbohydrate-electrolyte drink, or a 4% carbohydrate-electrolyte drink containing 1% glycerol, during each 60-h session. During exercise, the rating of perceived exertion and heart rate were similar for all beverages and all sessions, but oxygen consumption, core body and average skin temperatures, and sweat rate differed among beverages and sessions. Water alone appeared to provide adequate hydration for working in desert conditions over the 60 h when compared to carbohydrate-electrolyte beverages, with or without a small amount of glycerol.