All summer long I’ve been reading the social-media complaints of so many
runners this summer about the heat and humidity! But now, the sun is rising later and setting earlier. August
is over. September is coming. That means autumn is coming too – in about 23 days! If you haven’t figured it out by now, you have a very short time left to
reap the benefits of “heat acclimatization.”
The common phrase is “beat the heat”. But when most people
say that, they mean ‘stay inside in the air conditioning.” I like to beat the
heat by meeting it head on. During the week, I run around noontime – all year
long. But aside from that typical late-April heat wave, the heat doesn’t bother
me. Don’t get me wrong, it does wreak havoc on my performance; that’s just plain
physics. But by taking advantage of heat acclimatization (i.e., running at noon
every day as spring turns into summer) I don’t mind being out in the heat of an
August afternoon. I’m also looking forward to the aftereffects, as the days
cool off and I still have the superpowers I built up during the summer.
Super powers? Do I have your attention now? OK, science
time! Heat acclimatization is the adaptation of your body in response to heat
stress in a natural environment. These adaptations include reductions in heart
rate, body temperature response, skin temperature response, and perceived
exertion. These adaptations also include increases in sweat rate, sweat onset, cardiovascular
function, and overall ability to perform in the heat.
You become a better sweater: You start to sweat sooner, and
you sweat out more. Also, the sodium content of your sweat decreases, which
helps prevent dehydration. The result of better sweating? Better cooling!
Your cardiovascular function improves: Your body develops an
increase in plasma volume, improved blood flow, a decreased heart rate, and an
increased blood volume per heartbeat. What’s the point of all this? When you
exercise in the heat, there are two conflicting duties for your blood: 1)
oxygenate the muscles; 2) dissipate heat from the skin. Obviously, when you are
exercising in the heat, your need for both increases. With an increased blood volume,
your heart has more blood to pump around your body so it can do both of these
better at the same time.
The good news: if you exercise for about an hour a day in
the heat, it takes an average of two weeks to acclimatize.
The bad news: heat acclimatization goes away just as fast
(or faster) than it arrives after the stimulus of training in the heat is gone.
More good news: Imagine for a moment your body all hopped up
on heat acclimatization, and suddenly it’s no longer that hot. If you time it
right, you will still have all those cardiovascular benefits when its time for
those key fall races! Training for a spring or summer race during the winter?
Trick your body into early heat acclimatization by over-dressing so that you’re
very warm even though the weather is still cool.
Finally – be smart! Don’t start by going out in the noon heat
to get acclimatized! You’ve got to work up to it. Start off during the cooler
parts of the day and gradually work up to full heat. And stay properly hydrated
and electrolyted. Weigh yourself nekkid before and after your exercise; for
each ounce of weight lost, drink an ounce of water. And dress for the weather
in wicking, technical fabrics.
You’ve got three weeks until autumn arrives. Let’s see if
you can head into fall with a full supply of heat acclimatization!
Here are some scientific references if you are so inclined:
