Stofan, J. R., Stover, E. A., Lovett, S. C., Horswill, C. A., & Murray, R. (2006). A carbohydrate-electrolyte drink attenuates decline in blood sodium during prolonged exercise in the heat. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1507.

This study determined the rate of change in blood sodium with the consumption of fluid with or without electrolytes during continuous moderate-intensity cycling exercise in the heat. Adult male endurance athletes (N = 7) completed three hours of cycling at 55% of VO2peak in the heat , during which they consumed either a carbohydrate drink or carbohydrate-electrolyte beverage in equal volume. Drinks were consumed every 15 minutes equivalent to the rate of fluid loss determined in a preliminary trial. Whole venous blood sodium was analyzed at baseline, 15 minutes, and then at 30 minute intervals on a clinical electrolyte analyzer. Plasma volume changes were determined from Hct and Hgb measures. Sweat loss was determined by body mass change, and sweat by the regional skin patch technique, corrected to whole body values.

Carbohydrate-electrolyte beverage intake closely matching sweat loss slowed the decline in blood sodium and maintained plasma better compared to a carbohydrate beverage not containing electrolytes during prolonged exercise in the heat.

Implication. Sodium intake is important when performing prolonged exercise in the heat.

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