[Skip to Content]
Access to paid content on this site is currently suspended due to excessive activity being detected from your IP address Please contact the publisher to request reinstatement.
[Skip to Content Landing]
September 7, 1984

Influence of Hydration Level and Body Fluids on Exercise Performance in the Heat

Author Affiliations

From the US Army Research Institute of Environmental Medicine, Natick, Mass.

JAMA. 1984;252(9):1165-1169. doi:10.1001/jama.1984.03350090041020

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)