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Exercising in the heat: What you need to know

Exercising in heat

You might be thinking about going for a long jog in the heat.

Or a short jog. Or mowing the lawn. Or maybe just a short stroll at the zoo.

Either way, it’s hot out. And that means being extra-careful when it comes to exercise and other physical activity.

“Heat can do a lot of things to our bodies,” says Andrew Porter, DO, with Via Christi Sports Medicine. “It’s important to understand that and know how to prepare for activity in the heat, and to know if you’ve gone too far.”

Here is Dr. Porter’s guide for dealing with the heat.


Dr. Porter’s recommendations for staying hydrated before activity outdoors:

  • 16 ounces of fluid one to two hours prior to the activity
  • 16 ounces about 20 minutes before the activity
  • 4 to 8 ounces every 20-30 minutes during the activity

How hot is too hot?

Marathons, triathlons and other outdoor sporting events use what is called the wet bulb globe temperature, a combination of temperature, humidity, wind and radiation measured by a special device. (If that measure is over 82, most events are called off.)

Without that device readily available, Dr. Porter says a good rule of thumb is if it’s over 95 degrees, be careful.

“With a temperature that high, it’s harder for your body to lose heat, and easier for your body to gain heat, “ Dr. Porter says. “You might want to consider exercising early in the morning or later at night.”

But he says it’s not a one-size-fits-all guideline. Some people — especially those who are acclimated to the heat through regular exercise in it — know their personal limits.

What happens to your body when you overheat

  • Your body loses both fluids and electrolytes through sweat to become dehydrated.
  • If you lose too much electrolytes and fluids, your heart might not be able to pump enough blood to your brain. You may become lightheaded, delirious and confused.
  • Also, with a loss of electrolytes and fluids, your muscles won’t work as well. If the heat illness gets bad enough, your muscles can start breaking down and release proteins that can overwhelm organs, especially your kidneys.
  • A rise in core body temperature can also cause damage to your internal organs.

“Our bodies were made to be in balance,” Dr. Porter says. “When he get out of balance, even a little bit, it’s easy for it to spiral out of control if you get too dehydrated.”

What to do when you overdo it

The common symptoms of heat-related illness are lightheadedness, heat cramps, thirst, elevated body temperature and increased heart rate.

“The best thing you can do is prevention,” Dr. Porter says. In addition to hydration, he suggests wearing loose-fitting clothing, hat or visor, sunglasses and sunscreen.

But if you find yourself with symptoms of heat illness, here’s a plan to recover:

  • Remove yourself from the situation by finding shade or air conditioning.
  • Lie on your back and lift your legs above your head to allow blood to rush back to your brain to improve lightheadedness and cognition.
  • Stretch to relieve the muscle cramps.
  • Drink water or electrolyte fluids.
  • Take a cold shower (but be sure not to decrease your body temperature to the point of hypothermia).

Watch your meds

Some medications, and especially antihistamines for allergies, can contribute to heat-related illness. If you’re planning on a long run in the heat or to run a competitive 5K, you might consider letting the antihistamines get out of your system before your exercise.