As unprecedented heat waves become more
common, exercisers increasingly have to weigh the joys versus the risks of an
outdoor workout.
There’s no simple answer to the question of
how hot is too hot. A person’s ability to stay safe while exercising in the
heat depends on many factors such as age, usual exercise routine, workout
environment and intensity and whether that person is used to being active in
the heat, said Stavros Kavouras, director of the Hydration Science Lab at
Arizona State University.
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Exercising in humid heat poses unique
challenges, he said, but being active in dry heat can be just as risky.
Even when you’re at rest, your body
produces heat — and the amount increases as your muscles burn fat and
carbohydrates when you exercise. The harder you work, the hotter your body
gets.
If the temperature outside is greater than
90 degrees or if the sun is shining, your body will also be heated by the
environment, Kavouras said.
“As you’re adding this huge external heat
source, the body’s got to deal with that,” said Glen Kenny, a physiologist who
studies the body’s stress response at the University of Ottawa.
The main way the body sheds heat is through
the evaporation of sweat, which cools the surface of the skin, Kavouras
explained. In dry heat, sweat can evaporate so quickly that you may not notice
it.
During high-intensity exercise, most people
lose 1.5 to 2 liters of water per hour, although some people can lose even
more. As a person becomes dehydrated, sweat production slows and it becomes
harder to cool off. Those who exercise less regularly, who aren’t used to the
heat, are sleep-deprived, are sick or are older have more trouble cooling off.
Try to exercise during the coolest time of
the day, which is often the early morning in dry heat regions, said Dr. Jill
Tirabassi, a physician with expertise in sports medicine at the University at
Buffalo in New York. Seek out shade and wear porous, light-colored clothing
made of a moisture-wicking material. The more bare skin the better.
Avoid cotton, which holds onto water rather
than allowing it to evaporate, and backpacks, because you produce a lot of
sweat around your spine that can get trapped, Kavouras said.
If you exercise and start to feel unwell,
stop, rest in the shade and remove excess clothing, Tirabassi said. Symptoms of
heat-related illness can include cognitive or mood changes, rapid pulse, headache,
tunnel vision, dizziness, fainting or nausea.
Feeling cold or developing goose bumps are
clear signs of a medical emergency, Kavouras said. Cool down by drinking cold
fluids, spraying yourself with water, covering yourself with a cold towel or
taking a cold shower. Work out with a partner in case one of you starts to feel
sick.
Even if you don’t feel yourself sweating as
you exercise, drink lots of water, Kenny said. The most you want to drink is
about 1.5 liters of water an hour, which is the body’s absorption limit,
Kavouras said. If you plan to do high-intensity exercise in the heat for over
an hour, consider a hydration drink with added electrolytes — minerals such as
sodium, potassium and magnesium — to replace what you lose, Kavouras said.
Otherwise, you can experience cramping, dizziness and become prone to fainting,
he said.
Sodium is especially important. “If you’re
an athlete, especially if you exercise in a hot environment and you sweat
profusely, you do need a lot,” he said.
If you exercise in the high heat and your
body isn’t used to it, be sure to give yourself ample time to rest between
workouts, too. Consider not exercising every day.
“If you push your body day after day, there
is a progressive deterioration in your body’s ability to dissipate heat,” Kenny
said. “Your body needs to recover.”
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