Fluid and electrolyte supplementation for exercise heat stress

During exercise in the heat, sweat output often exceeds water intake? resul ting in a body water deficit (hypohydration) and electrolyte losses. Becaus e daily water losses can he substantial, persons need to emphasize drinking during exercise as well as at meals. For persons consuming a normal diet, electrolyte supplementation is not warranted except perhaps during the firs t few days of heat exposure. Aerobic exercise is likely to be adversely aff ected by heat stress and hypohydration; the warmer the climate the greater the potential for performance decrements. Hypohydration increases heat stor age and reduces a person's ability to tolerate heat strain. The increased h eat storage is mediated by a lower sweating rate (evaporative heat loss) an d reduced skin blood flow (dry heat loss) for a given core temperature. Hea t-acclimated persons need to pay particular attention to fluid replacement because heat acclimation increases sweat losses, and hypohydration negates the thermoregulatory advantages conferred by acclimation. it has been sugge sted that hyperhydration (increased total body water) may reduce physiologi c strain during exercise heat stress, but data supporting that notion are n ot robust. Research is recommended for 3 populations with fluid and electro lyte balance problems: older adults, cystic fibrosis patients, and persons with spinal cord injuries.