Hypohydration and exercise: effects of heat acclimation, gender, and environment

Abstract

This study examined the effects of heat acclimation and subject gender on treadmill exercise in comfortable (20 degrees C, 40% rh), hot-dry (49 degrees C, 20% rh), and hot-wet (35 degrees C, 79% rh) environments while subjects were hypo- or euhydrated. Six male and six female subjects, matched for maximal aerobic power and percent body fat, completed two exercise tests in each environment both before and after a 10-day heat acclimation program. One exercise test was completed during euhydration and one during hypohydration (-5.0% from baseline body weight). In general, no significant (P greater than 0.05) differences were noted between men and women at the completion of exercise for rectal temperature (Tre), mean skin temperature (Tsk), or heat rate (HR) during any of the experimental conditions. Hypohydration generally increased Tre and HR values and decreased sweat rate values while not altering Tsk values. In the hypohydration experiments, heat acclimation significantly reduced Tre (0.19 degrees C) and HR (13 beats X min-1) values in the comfortable environment, but only HR values were reduced in hot-dry (21 beats X min-1) and hot-wet (21 beats X min-1) environments. The present findings indicated that men and women respond in a physiologically similar manner to hypohydration during exercise. They also indicated that for hypohydrated subjects heat acclimation decreased thermoregulatory and cardiovascular strain in a comfortable environment, but only cardiovascular strain decreased in hot environments.

A Study of the Workload of Underground Trammers in the Ranigang Coal Field Area of West Bengal, India

“…Early disorders due to environmental stress combined with other factors cannot not be ignored, either, if serious impairment of miners' health is to be prevented [7]. Miners' hydration is important in underground hot environments, since dehydration reduces the physical capacity to work efficiently [8]. Involuntary dehydration does not occur in well-informed miners [9].…”

Factors which alter human physiological responses during exercise-heat acclimation

“…Women also appeared to have a higher central thermoregulatory set point than men, and therefore were more intolerant of hot-dry environments. However, significant differences were generally not found between the genders in subsequent experimentation for HR, core temperature and sweat loss during ,dditional hot-wet and hot-dry experiments (19).…”

Physiological and Cognitive Factors Related to Human Performance During the Grand Canyon Rim-to-Rim Hike

“…As Sawka, Montain, and Latzka (2001) report in a review of the field, core body temperature rises on average 0.1-0.25˚C for every percent of dehydration-induced body weight loss, with even larger increases seen when physically exerting oneself in hot conditions (Adolph et al, 1947;Montain & Coyle, 1992;Sawka, Young, Francesconi, Muza, & Pandolf, 1985;Strydom & Holdsworth, 1968). Being fit and accustomed to hot environments normally lends one a performance advantage; hypohydration (e.g., 5% body weight reduced) negates that advantage (Buskirk, Iampietro, & Bass, 1958;Cadarette, Sawka, Toner, & Pandolf, 1984;Sawka, Toner, Francesconi, & Pandolf, 1983). Under heat stress and hypohydration, overall cardiac output is decreased as heart rate increases but stroke volume decreases (see Sawka et al, 2001).…”