Voluntary dehydration in man

Abstract

The effects singly and in combination of heat, exercise, and hypohydration upon voluntary dehydration were studied in four acclimated, physically fit, young men. Voluntary dehydration is the delay in complete rehydration following water loss. Hypohydration refers to the state of decreased water content while the osmotic concentration of the body is maintained. Ad libitum drinking during the heat experiments was 146% greater than it was in the cool experiments. Hypohydration increased drinking 109% over the corresponding hydration experiment, exercise increased water intake 41% over resting. Hypohydration and exercise were less effective than heat in stimulating drinking. During the 4-hr experimental periods, the subjects did not or could not drink enough to compensate for the water lost. Regardless of the magnitude of the water deficit at the beginning of the recovery periods, the rates of rehydration were the same. The more stressful the experiment, the greater the water consumption and, in general, the longer it took to regain the lost water. water balance; heat; exercise; drinking; hypohydration Submitted on September 8, 1964

Sodium Replacement and Plasma Sodium Drop During Exercise in the Heat When Fluid Intake Matches Fluid Loss

“…However, it is well-established that thirst perception is an insufficient means to match fluid losses during exercise. 28 In addition, a body mass reduction of 3% or even less during 16 km of walking or running under the extreme environmental condition of heat stress 29 or during a marathon 30 has been associated with a decrease in plasma volume. These studies suggest that restoration of fluids lost via sweating should be promoted during prolonged, moderate-intensity exercise in the heat to ensure cardiovascular and thermoregulatory stability.…”

Impact of beverage acceptability on fluid intake during exercise

“…However, simply providing access to water is often not sufficient to prevent progressive hypohydration. This voluntary dehydration has long been observed in adults (Greenleaf & Sargent, 1965;Rothstein et al, 1947), and has recently been described in children (Rivera-Brown et al, 1999;Wilk & Bar-Or, 1996). Failure to maintain proper hydration has been a concern of the military (Mudambo et al, 1997), of the athletic community (Maughan, 1997) and to workers in industrial settings (Bernard, 1996) because of the negative consequences of dehydration on physiological and psychological performance.…”

Rehydration with drinks differing in sodium concentration and recovery from moderate exercise-induced hypohydration in man

“…Humans tend not to replace enough fluid to offset sweat losses either during, or immediately following exercise, resulting in some degree of hypohydration (Pitts et al 1944;Greenleaf and Sargent 1965;Greenleaf 1992;Maughan et al 2004;Passe 2001). If this water deficit is not replaced before subsequent exercise, exercise performance may be impaired (Burge et al 1993).…”