How Cold is Too Cold to Train Outside?

Kelly O'Mara
by Kelly O'Mara
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How Cold is Too Cold to Train Outside?

Before you add another log to the fire, pile on more blankets and insist it’s too cold to go out for a run, John Castellani would like you to remember: “People have walked to the poles.”

Castellani, an exercise research physiologist at the Army Research Institute of Environmental Medicine, has extensively studied the effects of physical activity in the cold. “I would argue as long as you have the right gear and clothing,” there’s no such thing as too cold to workout, he said — at least not until you start to approach arctic conditions.

It sounds hard to believe. We tend to be worried about the cold and the damage it could do. “People sometimes think the cold air will freeze the lungs,” says running coach Jack Daniels.

But that’s not the case. Our lungs can handle cold air. And as long as we prepare and warm up, our bodies can, too.

In Minnesota, “we run all winter long,” says Sarah McInerney, the operations manager for the Minnesota Distance Running Association, even in the cold and snow and freezing temperatures. The only time the organization cancels group runs is when it’s 25 below with a windchill.

Yet, how cold is too cold is a hot topic and a very personal decision for most of us. Some people will run in the snow and a few might complete marathon in below-zero temps — the stories of these seemingly superhuman feats are out there.


While there are a number of issues related to working out in the winter, the two main dangers are hypothermia and frostbite, according to research Castellani did on Olympic athletes.


However, in most conditions on land, hypothermia is not a major threat, especially if you’re generating heat from exercise and are not wet. That risk changes drastically with swimming or when we get wet, because of how our body regulates temperature. “The greatest risk of hypothermia during Olympic events may not be during the Winter Games. Participants in long-distance, open-water swimming events might be at the greatest risk of hypothermia of all Olympic athletes,” wrote Castellani in that study.

On land, as long as you dress adequately and generate enough body heat, you should be able to avoid hypothermia in temperatures above 25 below zero. You can also do a light warm up inside to get your core temperature up before you put on dry warm clothes and head outdoors. The danger comes when you dress for a hard run and then drastically slow down, because then your core temperature will drop. There are stories of racers experiencing hypothermia during marathons or ultramarathons, not because of the temperatures outside but because they became extremely fatigued and their bodies couldn’t sufficiently heat themselves anymore.

If you go hard and then slow down, you’ll have created sweaty clothes, which will cool you off even faster. That’s why adequate gear means layers: a base wicking material, topped with insulation and something windproof or waterproof on top depending on your activity. You actually want to be slightly chilly when you walk outside (or be prepared to take off layers before you get too warm), so you don’t overheat and sweat. Also, don’t hang around outside after you’re done, as your core temperature is coming down and the sweat starts to freeze.



The bigger danger, though, is frostbite, which has the greatest risk beyond 17–18 degrees below zero. That danger is highest for your extremities or for exposed skin, especially if it gets wet. “Frostbite is the most dangerous issue,” said Castellani.

That’s why you should wear gloves, warm socks and a hat. McInerney even puts Vaseline on her face if it’s exposed and duct tape on her shoes to keep the wind out.

People with circulation issues have a higher risk of frostbite. There are also those with respiratory issues who can find the dry, cold air problematic. (Often a scarf or mask over the mouth can help keep the air warmer and more moist.) But if you’re not predisposed to asthma attacks or circulation problems, then the cold should be manageable for most athletes.

Even the risk of muscle strains isn’t as great as most people fear, says Castellani. Just because it’s cold outside doesn’t necessarily mean your muscles are cold — especially if you do a good winter warmup first.

“Consider cross-country skiers who certainly compete and breathe hard, often in very cold conditions,” says Daniels.


Daniels, however, has his runners hit the treadmill occasionally during the winter months because of other risks: slipping on ice and falling, not accounting for the extra effort it takes to run in the snow and sleet or even getting lost. (It’s important not to get halfway into a workout and be unable to make it back, because then you risk getting dangerously cold.)

However, if you prepare well, there are also benefits to getting outside and getting some vitamin D during the darker months. Plus, you’ll be treated to empty running trails and pristine snowscapes.

“Winter running is great,” says McInerney, our Minnesotan. Just get off the couch and get out there.


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About the Author

Kelly O'Mara
Kelly O'Mara

Kelly is a professional triathlete and reporter outside San Francisco, where she is an on-call producer for the local NPR station. Her works appears regularly in espnW, Competitor, Triathlete and California Magazine. She also co-hosts the podcast, Locker Room Talk, for WiSP: The Global Women’s Sports Network. And she trains. A lot.


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