Morris, D., Huot, J., Jetton, A., Collier, S. & Utter, A. (2013. Effects of sodium ingestion on voluntary water consumption, hydration, and exercise performance in the heat. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 306.

This study determined the effects of sodium ingestion on ad-libitum, pre-exercise fluid consumption, hydration, and subsequent exercise performance in the heat in males (N = 9). Ss completed an exercise test to exhaustion on an electronically braked ergometer to determine VO2max power output. Ss returned on three occasions receiving one of three treatments: i) 60 mg/kg bm NaCl supplementation, ii) an equal volume of placebo, or iii) no treatment all followed by a two-hour hydration period in which they consumed water ad-libitum. Immediately following the hydration experience, Ss began a one-hour ride at 50% of maximum power output, followed immediately by a 200 kJ time-trial. Ambient temperature during these periods was 30°C. Fluid consumption and urinary output during hydration were measured and used to calculate fluid retention. Nude body mass was measured prior to and at the end of hydration and immediately following the 50% maximum power output and time-trial exercises to determine hydration status. Elapsed time to complete the time-trial was used as a performance measure.

Ss consumed significantly more water during hydration in the sodium (NaCl) condition when compared to the placebo and no-treatment conditions. Fluid retained at the end of hydration was significantly greater in the sodium condition when compared to the other two. Dehydration rate at the end of the 50% maximum power output ride was significantly lower in the sodium condition than in the other two. The time-trial was completed significantly faster in the sodium condition than in the other two. No significant differences were detected between the placebo and no-treatment conditions for any of the variables.

Implication. Acute sodium ingestion can enhance voluntary fluid consumption leading to hyperhydration and improved exercise performance in the heat.

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