Serum sodium concentration returns to normal
Fluid supplementation is necessary for exercise in which fluid losses must be offset by intake to avoid the negative effects of hypohydration on health and performance. Several aspects of gastrointestinal function have been studied to gain information concerning the assimilation of ingested fluids to maintain fluid balance during exercise. Research results with regards to gastric emptying and secretion, intestinal absorption and secretion, and aspects of fluid retention, including urine production and plasma volume changes, can be utilised to formulate an appropriate fluid supplementation regimen. Increasing the volume of ingestate and decreasing the carbohydrate concentration promote gastric emptying of fluids. By maintaining a low osmolality secretion is reduced, thus leading to a greater rate of net fluid absorption. Adding sodium and carbohydrate (up to approximately 7%) increases the net intestinal absorption rate. Increasing carbohydrate concentration above this level begins to have a deleterious effect on intestinal absorption of fluid. Sodium also promotes retention of ingested fluids and leads to an increased plasma volume response during rehydration. The primary goal of supplementation should be considered, fluid vs carbohydrate provision, and the beverage composition altered accordingly. Beverage composition to maximise fluid provision will not maximise carbohydrate availability.
