Tips for Running in Humidity
It’s not (just) the heat that matters! Here’s how to cope with the muggy weather.
By Liz Plosser, Runner’s World
Runners often obsess over weather reports, tracking the coolest time of day in which to run. But as anyone who’s ever tried to finish a five-miler in steamy conditions knows, it’s not just the temperature that matters, it’s the humidity.
"Of all the climate measurements we take to assess heat risk for our runners, humidity is the biggest factor," says George Chiampas, D.O., the medical director of the Chicago Marathon. Humidity makes warm summer runs even more taxing because the higher the moisture content of the air, the hotter it feels. An 88-degree day with a relative humidity just under 40 percent, for example, will feel like 88 degrees. Hot, yes, but when humidity reaches 70 percent, that same 88 temperature feels like 100 degrees.
Unless you’re lucky enough to live in Paradise, Nevada—the least humid city in the U.S.—here’s how to cope when running in steamy conditions.
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Why Humidity Matters
When you run, your core body temperature naturally rises, and your sweat glands produce droplets that carry excess heat to the surface of the skin, where it evaporates. But humidity prevents sweat from evaporating, so the heat stays put. “On a hot, humid day with no breeze, you have lost a key way to get rid of your building body heat, which can make running dangerous,” says Michael Bergeron, Ph.D., a professor at the Sanford School of Medicine of the University of South Dakota.
If your body heats up and gets more and more dehydrated, it goes into survival mode, maintaining blood flow to your essential organs (to keep you alive) and to your skin (to regulate temperature). Less blood will flow to your GI tract, which will make the digestion of sports drinks or gels difficult, and you may feel nauseous as a result. You may also find you are more prone to side stitches when you are overheated—especially if your breathing becomes shallow and uneven. And your heart rate will escalate as your ticker and lungs work overtime trying to deliver oxygen throughout your body, Dr. Chiampas says.