[Fluid and sodium balance during exercise--standpoint].

During exercise certain metabolic and physiological processes influence fluid and electrolyte balance. Fluid loss, mostly through sweating, that is not properly compensated for by drinking, may result in dehydration. Clinical manifestations of dehydration depend on the amount of fluid lost. The more severe the level of dehydration is, the greater the reduction in physical and cognitive performance. It is recommended to drink water frequently and in small amounts. In order to encourage drinking, the fluid should be cool, palatable, readily available, and not carbonated. During exercise the ability of the kidney to excrete water is restricted, and therefore, there is a risk of hyperhydration and hyponatremia, mainly under conditions of overdrinking. Sodium loss through sweating and the development of hyponatremia will primarily occur during strenuous exercise lasting more than 4 hours. Symptoms of hyponatremia will generally appear at sodium concentrations below 130 mmol/l. In order to avoid hyponatremia one must avoid overdrinking, and during prolonged physical activity (> 4 hours) sodium intake must match the amount lost by sweating. Proper electrolyte and carbohydrate consumption through a normal diet is preferable to sport beverages or exogenous sodium supplements. In order to avoid dehydration, on one hand, and hyponatremia due to hyperhydration, on the other hand, the amount of fluid consumed should complement the amount of fluid lost during exercise. Given that there is intra- (depending on the type of activity and environmental conditions) and interindividual variability in the rate of fluid and salt loss, fluid and salt intake should be determined on an individual basis, as outlined in this standpoint.