Journal of Applied Physiology, Vol 48, Issue 6 999-1007, Copyright © 1980 by American Physiological Society
Thermoregulation during rest and exercise in different postures in a hot humid environment
K. Kabayashi, S. M. Horvath, F. J. Diaz, D. R. Bransford and B. L. Drinkwater
The time course of whole-body sweating and thermal regulation during rest
and exercise in a hot humid environment was investigated in three body
postures. After 45 min rest in the upright, low-sit, or supine posture,
five unacclimatized men exercised for 45 min on a bicycle ergometer in the
same posture in an environment of 49.5 degrees C, 28.9 Torr. Exercise was
performed at two different work loads, corresponding to about 30 and 45% of
VO2max. During exercise auditory canal temperature, rectal temperature, and
mean skin temperature increased linearly being highest in the supine and
lowest in the upright posture. Percentage of evaporated sweat from the skin
to secreted sweat was 65% in upright, 52% in the low-sit, and only 46% in
the supine posture during the last 20 min of exercise regardless of work
load. The time course of the rate of body heat storage was different from
predictions based on the thermal balance equation. Evaporative heat loss
was not 100% effective in cooling the skin surface.
