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Researchers
have learned that aerobic exercise in air temperatures as
low as 65 degrees F can increase your body's core temperature.
Your heart rate increases as your body's core temperature
increases. Blood moves away from muscle toward the surface
of the skin. The depletion rate of body water from sweating
increases. This combination decreases your ability to perform
and increases your probability of heat injury.
Air
temperatures of 88 degrees F and higher stress the body's
heat transfer mechanism to the limit, and if left unmanaged,
exercise in these conditions can raise your core temperature
to a dangerous level. Heat cramps are the mildest and most
common form of heat related injury.
Core
body temperatures at 106 degrees F are a life-threatening
medical emergency. At excessive core temperatures you can
suffer heatstroke, when the sweating mechanism shuts down
and the skin gets hot and dry. Fever thermometers are not
standard exercise gear but it's not a bad idea to occasionally
bring one along and check your core temperature immediately
after completing an exercise session. You can learn if you
have to be more aggressive about managing your body temperature.
Sweating
is the body's most important heat transfer mechanism. Any
condition that slows or blocks the transfer of heat from the
body by evaporation causes heat storage, which results in
an increase in body temperature. Light weight, loose fitting
clothing is the best way to handle this. Performance fabrics
like Coolmax wick moisture away from the skin while allowing
air to pass through.
Relative
humidity also directly affects evaporative cooling. At 100%
relative humidity the air is completely saturated with moisture.
Sweat does not evaporate and no cooling effect takes place.
Consequently, the body's core temperature rises, which triggers
even more sweating. The net effect is an even more rapid loss
of body water... the sure recipe for dehydration and potentially
serious problems.
According
to U.S. Army physical training manuals plain water is the
best replacement fluid to use to prevent dehydration. Fluids
with high sugar content slow the absorption of water from
the stomach and should be avoided.
To
prevent heat injuries, the following hydration guidelines
should be used:
Drink
13 to 20 ounces of cool water at least 30 minutes before exercise.
Drink 3 to 6 ounces at 15 to 30 minute intervals during exercise.
Drink to satisfy your thirst, and then some, after exercise.
Cool
water between 45 to 55 degrees F is absorbed more quickly.
You
do not have to work as hard in high temperatures to achieve
a training effect. Increased temperatures and humidity cause
increased heart rates. Consequently, it takes much less effort
to elevate the heart rate into the training zone, but the
training effect is the same. These facts underscore the need
to monitor both your body temperature and your heart rate
when running or performing other aerobic exercises during
the summer and in hot climates.
About
the Author
(c)
2006 by Peter Somerville. Peter is a former military officer,
attorney, writer, and the creator of The
Paratrooper's Guide To Fitness and Weight Loss. Now anybody
can take advantage of the world's most carefully researched
and successful physical fitness and weight loss training program
at http://lean-and-mean.net
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