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Article |

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


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