THERMAL AND CARDIOVASCULAR STRAIN FROM HYPOHYDRATION - INFLUENCE OF EXERCISE INTENSITY

This study determined the effects of exercise intensity on the physiol ogic (thermal and cardiovascular) strain induced from hypohydration du ring heat stress. We hypothesized that the added thermal and cardiovas cular strain induced by hypohydration would be greater during high int ensity than low intensity exercise. Nine heat-acclimated men completed a matrix of nine trials: three exercise intensities, 25%, 45% and 65% (V) over dot O(2)max; and three hydration levels, euhydration and hyp ohydration at 3% and 5% body weight loss (BWL). During each trial, sub jects attempted 50 min of treadmill exercise in a hot room (30 degrees C db, 50% rh) while body temperatures and cardiac output were measure d. Hypohydration was achieved by exercise and fluid restriction the da y preceding the trials. Core temperature increased (P<0.05) 0.12 degre es C per%BWL at each hypohydration level and was not affected by exerc ise intensity. Cardiac output was reduced (P<0.05) compared to euhydra tion levels and was reduced more during high compared to low intensity exercise after 5% BWL. It was concluded that: a) the thermal penalty (core temperature increase) accompanying hypohydration is not altered by exercise intensity; and b) at severe hypohydration levels, the card iovascular penalty (cardiac output reduction) increases with exercise intensity.