Influence of Hydration Level and Body Fluids on Exercise Performance in the Heat
- Michael N. Sawka, PhD;
- Ralph P. Francesconi, PhD;
- Andrew J. Young, PhD;
- Kent B. Pandolf, PhD
Abstract
During exercise in the heat, sweat output often exceeds water intake, resulting in hypohydration, which is defined as a body fluid deficit. This fluid deficit is comprised of water loss from both the intracellular and extracellular fluid compartments. Hypohydration during exercise causes a greater heat storage and reduces endurance in comparison with euhydration levels. The greater heat storage is attributed to a decreased sweating rate (evaporative heat loss) as well as a decreased cutaneous blood flow (dry heat loss). These response decrements have been attributed to both plasma hyperosmolality and a plasma hypovolemia. Subject gender, acclimation state, and aerobic fitness do not alter the increased heat storage when hypohydrated. Hyperhydration, or body fluid excess, does not seem to provide a clear advantage during exercise-heat stress, but will delay the development of hypohydration.
(JAMA 1984;252:1165-1169)
Footnotes
-
Reprint requests to US Army Research Institute of Environmental Medicine, Kansas Street, Natick, MA 01760 (Dr Sawka).
