186 Training for Specific Environments
Training in Hot Environments
Exercising in hot, humid environment imposes a significant challenge on the body.
The human body maintains tight control of body temperature through several different
mechanisms. Under conditions which impose large heat loads (example: strenuous exercise
or wearing protective gear in a hot environment), the primary mechanism for cooling is
evaporation of sweat from the skin or evaporative cooling. Relative humidity is the most
important factor governing evaporative cooling: when the humidity is high, evaporation is
greatly limited.Your skin is like the radiator of a car; as the temperature of the body core rises it
warms the blood and pumps it to the skin to cool off. Sweat is released at the skin and
absorbs the heat from the warmed blood. As sweat is warmed, it is vaporized the same way
boiling water turns to steam and thus removes a large amount of heat from the body. Only
sweat that evaporates can effectively cool the body; sweat that “drips” is essentially wasted
fluid and provides little or no cooling effect. The body maximizes evaporative cooling by:" Increasing Heart Rate: An increase in the heart rate increases blood
flow to the skin and results in greater heat transfer to sweat and vapor." Increasing Sweat Volume: Beginning to sweat earlier and recruiting
more sweat glands increases the rate of sweat production, therefore cooling.How hot is too hot? The degree of danger posed by a hot environment is usually
determined by the wet bulb-globe temperature (WB-GT). If the WB-GT is over 87° F
(30.5° C) or if no WB-GT is available and the temperature is over 85° F with a relative
humidity of 60% or above, exercise should be avoided or undertaken with caution.Factors that Hinder Body Cooling in the Heat
" Humid Heat: As the humidity increases, evaporative cooling slows due to
saturation of the air with moisture." Skin Disorders: Injuries such as deep thermal burns, sunburn or rashes
will prevent or hinder sweating." Clothing: Any clothing that is impermeable to water vapor will compro-
mise cooling.Heat Acclimation