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Fluid Replacement and Heat Stress, 1993

Pp. 169-193. Washington, D.C.

National Academy Press


Solute Model or Cellular Energy Model? Practical and Theoretical Aspects of Thirst During Exercise

Roger W. Hubbard1, Patricia C. Szlyk, and Lawrence E. Armstrong


Most physiologists would agree that repaying the water debt incurred through evaporative cooling is part of the physiological cost of work in the heat. Pitts et al. (1944) emphasized that during work in the heat, men never voluntarily drink as much water as they lose and usually replace only two-thirds of the net water loss. Rothstein et al. (1947) observed that this occurred even when water was availabel and called this phenomenon voluntary dehydration. Some physiologists feel that voluntary dehydration occurs because “. thirst is an inadequate stimulus to drinking” (Ladell, 1965, p. 253). On the other hand, Vokes (1987) contends that “. one of the best examples of a perfectly functioning homeostatic system is water balance” (Vokes, 1987, p. 383). One of our goals is to reconcile the fact that under certain conditions both of these statements are correct. We will also try to switch the reader's interest from water to salt for, although man may drink, “. water cannot be held until the missing osmoles are made good”


Roger W. Hubbard, Department of the Army, U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760-5007

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