How to Exercise Safely in the Heat

As temperatures creep into the 90s and beyond, dehydration and heat exhaustion while exercising become a very real-and potentially dangerous-threat.

When is it safe to exercise outdoors?
It's important to watch the temperature, but the most relevant number you need to know before heading outdoors is the heat index, which takes humidity into account and represents how hot it feels.

The risk of muscle cramping and heat exhaustion rises as the heat index climbs above 90. Although less serious than heat exhaustion, cramping is dangerous, especially when you're dehydrated. 'When you start cramping and don't have enough fuel in the tank, that can lead to something more serious, like pulling a muscle,' Anderson says. When the index is higher than 100, heat stroke also becomes more likely.

In the Tampa Bay area, where Anderson conditions and trains high school football players, the index is almost always in the danger zone, and it's not uncommon for it to reach 105. It's really important to modify your exercise routine when the index is that high, Anderson says.

Anderson recommends scaling back the duration or intensity of your workouts once the hot weather hits. It takes about two weeks to get acclimated to exercising in the heat (especially if you're not in top shape to begin with), he says. After that period, you're free to gradually ramp back up.

When it's really hot out, Bergen advises, it's a good idea to take breaks more frequently, exercise in the shade whenever possible, and wear breathable and light-colored clothing.

Exercising in the heat is safe if you use common sense and follow some basic rules, Bergeron says. 'As long as they're not working [out] too hard, someone who is well rested, hydrated, and nourished can tolerate pretty tough conditions,' he says.

Stay hydrated
The most important thing to do while working out in the heat is to stay hydrated. That may seem obvious, but hydrating properly is more complicated than you may think.

For starters, you should drink plenty of fluids before and after your workout, not just during. Anderson tells his football players to hydrate throughout the day to prepare for their 4 p.m. practices, and to drink 16 to 20 ounces of water or a sports drink (like Gatorade) one hour before practice.

During your workout, you should consume 4 to 16 ounces of fluids every 15 to 20 minutes, according to the American College of Sports Medicine. Sports drinks-which contain lots of sugar and additives in addition to the electrolytes that help keep you hydrated-are most beneficial during prolonged exercise, Bergeron says, and it's sometimes wise to alternate them with water.

Don't rely on your thirst to tell you when to drink. 'People let thirst drive them to drink, but it isn't enough to match what they are losing [by sweating],' Bergeron says, adding that if you start feeling thirsty, you're already dehydrated.

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Tammy Worth
Last Updated: July 29, 2010

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