When it comes down to it, wearing the proper clothing is the most important factor.
As frigid temperatures take over most of the country, most people are staying indoors, figuring this must be too cold to run outside. In fact, though, research suggests that as long as it’s warmer than -18 degrees, it’s not too cold to work out—as long as you take the appropriate precautions.
“People, of course, have walked to the Poles,” said John Castellani, an exercise physiologist at the Army Research Institute of Environmental Medicine. Castellani was co-chair of a study conducted by the American College of Sports Medicine that found, “For the most part, cold-weather is not a barrier to performing physical activity.”
The main thing Castellani and his co-authors studied was the danger of frostbite, which has the highest risk below -17 or -18 degrees. But, he said, they also looked at other common fears about running or working out in the extreme cold.
While there are certain populations who are at risk, the vast majority of research suggests that people won’t damage their muscles or their lungs in the cold—two common misconceptions.
The group did find an increase incidence of asthma and cardiac stress in populations that are predisposed to those problems. Those with circulation issues can also have a high risk for frostbite even at warmer temperatures. Largely, however, people are able to run in freezing and below freezing temperatures without hurting themselves.
Of course, the caveat—and it’s a big one—is that you have to be appropriately prepared.
Making sure you dress for the weather is “one of the biggest things,” said Castellani. You should wear layers, particularly layers that stay dry. Once clothes get wet they can freeze and become dangerous for an athlete.
Castellani says a base layer of silk or synthetics should be covered by an insulating layer of fleece, synthetics or wool, and then topped with an outer wind-breaking layer if necessary. Mittens are typically better than gloves and it’s important to keep your feet dry as well. Many runners also use facemasks, hats or balaclavas in the extreme cold.
And, Castellani says, he often tells people to warm-up lightly inside (but not so much as to be sweaty and wet) and then layer up in dry clothes and head out. This can be particularly useful if you’re planning on doing anything hard or racing in the cold.
In addition to dressing well, it’s important to know the conditions. The most common ways people get hurt are simply by falling on ice or getting halfway out and not being able to make it back. That’s when a runner can find himself turning into a dangerously frozen icicle.
When Marisa Lindsay moved from California to Minneapolis, she had to test out what kinds of clothes to wear and how to layer appropriately. She also had to learn how to run on the snow. That was when Yaktrax, which strap onto shoes to allow you to gain traction, came in handy—but they only worked for a few miles until they too got clogged with snow.
“I still don’t have it figured out,” said Lindsay. During a 5K race in -7 degrees, she even found her eyelashes beginning to freeze together. “I know some people wear ski goggles, but I haven’t stooped to that yet.”
All those challenges mean that, while it can be done, plenty of athletes and coaches choose to simply not work out in the extreme cold, especially if they need to get in hard training.
“There’s a point when I say it gets too cold,” said Chicago-based coach Matt Johnson of Runner’s Academy.
Johnson urges his athletes to modify or change workouts based on the weather. Typically, unless you’re in the middle of the storm of the century or you live in Minnesota, there aren’t multiple weeks in a row of dangerous conditions. It can be easy to move workouts around then or to do some of them on the treadmill. If you do decide to run in the snow and ice, know that it will be significantly harder.
Running five miles in a few inches of snow takes a lot longer than running five miles on dry roads. In those cases, you may want to simply aim for time, not distance. And, if you’re planning something longer or harder, doing loops can ensure that you never get too far from your house in case you start to freeze or something goes wrong.
“There’s no shame in taking it indoors or doing something else,” said Johnson.
The most important thing if you’re stuck in a polar vortex, snowstorm, or bomb cyclone, besides having the right clothes, is to “be flexible,” he said. Change your plans if you need to change your plans. It’s better than becoming a cautionary frozen tale.
A version of this article originally appeared on Competitor.com.