When the temperature dips below freezing and the ground becomes a sheet of ice, the bitter cold wind drives many athletes and weekend warriors indoors.

But there are plenty of others who see the falling snow as a cue to put on their running shoes and head outside for some exercise. In fact, winter running has become a popular activity recently for people who compete in year round races, or for those looking to work off the added holiday pounds.

In fact, many companies that specialize in outdoor activities now sell shoes specifically designed for inclement conditions, with features like tapered bottoms to better grip icy ground and thick water proof shells designed to keep feet warm and dry.

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But what would possess someone to run outside in the cold when they could stay indoors and run on a treadmill?

“Ugh, not the treadmill,” Joe McAntosh, a 56-year-old Michigan native who’d rather bundle up than run inside, said. “I feel like a robot when I use that thing.”

McAntosh trains outside all winter, no matter what how low the temperature dips, and claims to love it.

"The cooler air is good for my muscles,” he said. “It keeps them from swelling up like they do in the summer.”

Melissa Polivka, who has already completed marathons in 30 states in her quest to hit 50, said she doesn’t take the season off simply because the weather is cold.

“The treadmill is so boring and hard on my legs,” Polivka, who sometimes runs with toe warmers in her shoes, told Fox News. “If it’s really bad, I put duct tape around the tops of my shoes to keep the snow out."

But, just because someone prefers to run in the cold than hit the treadmill, from a medical standpoint does that mean they really should?

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"For the most part, if you're healthy enough to run other times of the year and not suffering from cardiac issues or injuries, it's usually fine," Dr. Aneesh Garg, of Chicago Orthopedics and Sports Medicine, told Fox News. "Although cold weather can be an increased trigger for asthma sufferers."

Some of the preparations Garg recommends include "making sure to wear proper running clothes that keep your muscles warm. Use skin protection, such as Vaseline, to prevent wind burn. And wear sunscreen" because even though its winter, your skin can still burn.

Hydration is also key.

"Often athletes don't feel thirsty when they run in the winter because of the cold but you can still get dehydrated," Garg said.

Garg, who is a team physician for USA Hockey, said, however, that there is a time when people should not be running outdoors.

"If the ground is icy, if there's black ice, you can slip and fall, causing secondary injuries," he said.

Running coach Jenny Hadfield knows about cold weather exertion. Hadfield, an experienced runner and owner of CoachJenny.com, leads groups for marathons in Alaska and Antarctica, where the temperature can drop to a bone-chilling -40 degrees.

But being out in such frigid conditions without getting numb hands and chapped skin takes planning, Hadfield said. She suggests spending extra time warming up.

“Take at least 5 minutes to walk briskly before you start to run” she said. “It may take 10-15 minutes of running before you are completely warmed up and in your running tempo.”

She suggests shortening your stride and keeping your feet lower to the ground to reduce the risk of slipping, falling or straining muscles. She also recommends to avoid overdoing it with cold gear.

“Your body temperature increases as you run, so you don’t need many layers in most winter conditions,” Hadfield said.

Figuring out just the right wardrobe for Chicago winters was a challenge at first for Aparna Thakur, who grew up in New Delhi, India, where temperatures easily climb to over 100 degrees at times.

Now Thakur can be found hitting the frozen pavement at the crack of dawn.

“I find it magical to see all the ice formations on the lake,” she said.

For others, hitting the pavement while others have headed indoors can be relaxing.

“It’s so peaceful, it’s my form of meditation” adds McAntosh.