Voluntary dehydration and electrolyte losses during prolonged exercise in the heat.

The effects of water temperature (6 degrees, 22 degrees, 46 degrees C) and chlorination on voluntary dehydration (D), sweat electrolyte losses (SEL), and total body electrolyte losses (BEL) were studied in 12 healthy males during 6 h of intermittent treadmill exercise (1.34 m X s-1, 5% grade) in a climatic chamber (40.6 degrees C DB, 25.5 degrees C WB). Body weight (BW), rectal temperature (Tre), mean weighted skin temperature (Tsk), heart rate (HR), plasma osmolality (PO), sweat rate (SR), sweat sodium (Na+), chloride (Cl-), potassium (K+), and magnesium (MG++), urine volume, Na+, and K+ were measured. No differences were found between chlorinated and non-chlorinated treatments except SEL of Mg++. Subjects (Ss) who drank 46 degrees C (-2.1% BW) consumed approximately 50% less water (p less than 0.001), and had D which was 1.050 kg larger (p less than 0.001) than subjects who consumed 6 degrees C (-0.5 %BW). There were no significant between-group PO differences, but Tre and Tsk differed between 46 degrees and 6 degrees C (p less than 0.01), and the HR of 22 degrees and 46 degrees C were both different from 6 degrees C (p less than 0.05). SR of all groups were essentially equal, although differences in total sweat Na+ (p less than 0.02) and Cl- (p less than 0.04) losses were observed between 46 degrees and 6 degrees C. SEL of sweat K+ and Mg++ were not affected by the experimental design. Based on 24 h projections of BEL, it was concluded that K+ depletion is more likely than Na+ depletion because food is often supplemented with sodium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)