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Defence and Civil Institute of Environmental Medicine, Human Protection and Performance Section, North York M3M 3B9; Graduate Department of Community Health, University of Toronto, Toronto, Ontario, Canada M5S 1A8
The purpose of
the present study was to determine the separate and combined effects of
aerobic fitness, short-term heat acclimation, and hypohydration on
tolerance during light exercise while wearing nuclear, biological, and
chemical protective clothing in the heat (40°C, 30% relative
humidity). Men who were moderately fit [(MF); <50
ml · kg
1 · min1
maximal O2 consumption;
n = 7] and highly fit
[(HF); >55
ml · kg1 · min1
maximal O2 consumption;
n = 8] were tested while they
were euhydrated or hypohydrated by ~2.5% of body mass through
exercise and fluid restriction the day preceding the trials. Tests were
conducted before and after 2 wk of daily heat acclimation (1-h
treadmill exercise at 40°C, 30% relative humidity, while wearing
the nuclear, biological, and chemical protective clothing). Heat
acclimation increased sweat rate and decreased skin temperature and
rectal temperature (Tre) in HF subjects but had no effect
on tolerance time (TT). MF subjects increased sweat rate but did not
alter heart rate, Tre, or TT. In both MF and HF groups, hypohydration significantly increased Tre and heart rate and decreased
the respiratory exchange ratio and the TT regardless of acclimation
state. Overall, the rate of rise of skin temperature was less, while
Tre, the rate of rise of Tre, and the TT
were greater in HF than in MF subjects. It was concluded that
exercise-heat tolerance in this uncompensable heat-stress environment
is not influenced by short-term heat acclimation but is significantly
improved by long-term aerobic fitness.
heat exhaustion; temperature regulation; hypohydration
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