If you've been a slave to the tread so far this winter, here are a few science-backed reasons to consider heading outside.
Getty Images

The treadmill is often an unavoidable entity, especially in the dead of winter. (It's why we created our 30-Day Treadmill Challenge!) But as the weather warms up and running on your gym or home treadmill becomes less of a necessity, there are some clear benefits to taking your running workout outside, from stronger glutes to a happier heart. We combed through the studies and polled top experts to bring you all the ways running alfresco trumps running on the tread. (Psst: If you're brand-new to running, check out our beginner's guide to get started.)

You'll build more muscle.

Unless you're running on a self-powered treadmill like the WOODWAY Curve, outdoor running tends to be a slightly better butt-strengthener. That's because every time your foot lands in front of you on a typical treadmill, the belt brings your leg back underneath you-an action your glutes should ideally be in charge of, explains Pamela Geisel, M.S., C.S.C.S., a certified strength and conditioning specialist with the Hospital for Special Surgery's James M. Benson Sports Rehabilitation Center and Tisch Sports Performance. And, by running on hills outdoors (which yes, you can also simulate on the treadmill) you'll up the workload not just on your glutes, but all throughout your legs as well as in your core.

You'll burn more calories.

Running outside tends to require more energy than running on a tread. "Outdoors, you are changing surfaces constantly, fighting the wind, and making quick and sudden starts and stops, which all lead to increased caloric burn," says physical therapist Michael Silverman, director of rehabilitation and wellness at Northern Westchester Hospital. In fact, to burn as many calories on the treadmill as you would outside, you need to run at a 1 percent incline, according to research published in the Journal of Sports Sciences. And while we don't recommend running in extreme temps (heatstroke and frostbite can happen to even the most experienced runners!) it is worth noting that your body burns extra calories to regulate your body temperature, he says.

You'll cut your injury risk long-term.

While the softer surface provided by a treadmill does result in less impact on your bones and connective tissues, this isn't entirely a good thing, experts say. Theoretically, it could result in a lower injury risk (especially if you have less-than-perfect running form), but less impact also means that running won't stimulate quite as much bone growth, which, over time, could also result in injury, Geisel says. (Fun fact: It takes about 1/10 the force required to break a bone to trigger bone formation and growth.) Not to mention, if you have less-than-perfect running form and end up hovering too close to the console or holding on to the rails, you can also set yourself up injury, he says.

(Disclaimer: Of course, it's also important to consider what's going on outside your window when considering the risk of outdoor running. Rocky terrain, ice, snow, and rain can all increase the risk of slips, sprains, and falls, Silverman says. When running in the still-wintry weather, consider fixing cleats like Yaktrax Pro or Petzl Spiky Plus to your shoes. More on that here: How to Prevent the Most Common Running Injuries)

You'll be better prepared for your race.

When it comes to actually training for a race, this is yet another way that running outdoors trumps the treadmill. "You want to practice and prepare your body for what it is going to face on race day," Geisel says. And unless you're participating in an indoor triathlon, that means you need to head outside. Ideally, you should run part, if not all, of your race's course during training, Silverman says.

You'll have more energy.

There's no contest here. Research from the University of Exeter in the U.K. shows that when people run outdoors, they enjoy a significantly greater energy boost and drop in tension, anger, and depression compared to when they run indoors.

"When you run outside, there are typically changes in scenery, changes in direction, and a sense of exploration. You lose that when you take it indoors and complete your workout by running in place," Geisel says.

You'll improve your heart health.

As long as you're running at the same level of exertion (think: that 1 percent incline), your heart stands to get just as much out of your running workout, whether you're inside or out. But the added mood boost that you get from running outside (plus the vitamin D!) can actually improve your heart health over the long term, says Regina Druz, M.D., F.A.C.C., a cardiologist with the Integrative Cardiology Center of Long Island.