Hydration effects on thermoregulation and performance in the heat

During exercise, sweat output often exceeds water intake, producing a water deficit or hypohydration. The water deficit lowers both intracellular and extracellular fluid volumes, and causes a hypotonic-hypovolemia of the bloo d. Aerobic exercise tasks are likely to be adversely effected by hypohydrat ion (even in the absence of heat strain), with the potential affect being g reater in hot environments. Hypohydration increases heat storage by reducin g sweating rate and skin blood Row responses for a given core temperature. Hypertonicity and hypovolemia both contribute to reduced heat loss and incr eased heat storage. In addition, hypovolemia and the displacement of blood to the skin make it difficult to maintain central venous pressure and thus cardiac output to simultaneously support metabolism and thermoregulation. H yperhydration provides no advantages over euhydration regarding thermoregul ation and exercise performance in the heat. Published by Elsevier Science I nc.