Effect of water and electrolyte replacement during exercise in the heat on biochemical indices of stress and performance.

Eight healthy young men exercised on alternate days in a warm, humid environment (32 degrees C, 65% RH) at 50% VO2 max for 2 h while receiving a water supplement (WS), glucose-electrolyte solution (ES), or no fluid supplement (NS). The average weight loss after 2 h of exercise and NS was 2.44 kg with a resultant plasma volume decrease of 17%. This acute period of exercise with no fluid replacement elicited significant increments in serum levels of cortisol, dopamine-B-hydroxylase and uric acid. Alternatively, exercise in the heat for the same duration with water or electrolyte supplement failed to effect significant alterations in any of these physical or biochemical factors compared to preexercise levels. Heart rates under the influence of heat stress and exercise with NS averaged 18% higher at each time period studied compared with WS or ES.