Rehydration with drinks differing in sodium concentration and recovery from moderate exercise-induced hypohydration in man

Abstract

To investigate how differing moderate sodium chloride concentrations affect rehydration after exercise and subsequent exercise capacity, eight males lost 1.98 ± 0.1% body mass exercising in the heat, then consumed one of four drinks in a volume equivalent to 150% of mass loss. Drinks were identical except for sodium chloride content (1 ± 1, 31 ± 1, 40 ± 1, 50 ± 1 mmol/l). After 4 h recovery subjects cycled for 5 min at 70% $\dot{V} {\text{O}}_2$peak then at 95% $\dot{V} {\text{O}}_2$peak until volitional fatigue. Urine output was inversely related to sodium intake: more was produced with the 1 than the 40 and 50 mmol/l drinks (P < 0.01). Time to exhaustion in the exercise capacity test was not different between treatments (P = 0.883). The addition of 40 or 50 mmol/l of sodium chloride to a rehydration beverage reduced subsequent urine output, thereby providing more effective rehydration than a sodium-free drink. This did not, however, result in improved performance 4 h after the end of the rehydration period.