ABSTRACT
High ambient temperature and humidity reduce the capacity to perform prolonged exercise because of dehydration and thermoregulatory stress contributing to fatigue. Thermoregulatory sweating causes a reduction in plasma volume and elevated heart rate and core temperature. If no fluid is ingested during work, the plasma Na+ concentration and osmolality will increase (Armstrong et al., 1985). Fluid intake is important to maintain plasma osmolality in activities where dehydration and thermoregulation are of primary concern because reduced central blood volume reduces skin blood flow.
