Abstract des Autors

The influence of exercise intensity on thermoregulation was studied in 8 men and 8 women during three levels of arm-leg exercise (level I: 700 ml O2/min; level II: 1250 ml O2/min; level III: 1700 ml O2/min) for 1 h in water at 20 and 28 deg C (Tw). For the men in Tw 28 deg C the rectal temperature (Tre) fell 0.79 deg C during immersion in both rest and level-I exercise. With level-II exercise a drop in Tre of 0.54 deg C was noted, while at level-III exercise Tre did not change form the pre-immersion value. At Tw of 20 deg C, Tre fell throughout immersion with no significant difference in final Tre observed between rest and any exercise level. For the women at rest at Tw 28 deg C, Tre fell 0.90 deg C below the preimmersion value. With the two more intense levels of exercise, Tre did not decrease during immersion. In Tw 20 deg C, the women maintained higher Tre during level-II and level-III exercise compared to rest and exercise at level I. The Tre responses were related to changes in tissue insulation (It) between rest and exercise with the largest reductions in It noted between rest and level-I exercise across Tw and gender. For men and women of similar percentage body fat, decreases in Tre were greater for the women at rest and level-I exercise in Tw 20 deg. With more intense exercise, the women maintained a higher Tre than the men, especially in the colder water. These findings indicate that exercise is not always effective in offsetting the decrease in It and facilitated heat loss in cool or cold water compared to rest.