A treadmill offers more shock absorption than pavement or asphalt.

Treadmill runs don’t work the glutes and hamstrings quite as much as running over ground.

Your cadence typically speeds up on a treadmill.

There’s no air resistance while running in place on a treadmill. 

Uneven terrain outside challenges your stabilizer muscles more.

Outdoor runs can better relieve stress. 

A treadmill lets you control both the incline and your pace precisely.

Outdoor runners need to consider safety concerns, such as weather, darkness, and cars. 

You can keep water and fuel right on the treadmill console (and are probably always near a bathroom). 

Premium treadmills usually offer plenty of on-screen entertainment options. 

Outdoor routes can take you to interesting neighborhoods and scenery.

There’s more shock absorption. “Treadmills usually have more shock absorption and require less impact than the pavement or concrete,” Olivia says. This is especially true if you’re running on a treadmill with a cushioned belt, like the Peloton Tread+. “This makes running on a treadmill way easier on your knees, ankles, and joints.” It’s true: Research shows that treadmills have the highest shock-absorption capabilities compared to any other running surface.

You tend to run with a faster cadence. Research shows that, on a treadmill, runners typically use quicker, shorter strides. “That might be an effect of the belt facilitating the movement a little bit more,” says physical therapist Vikash Sharma, who works with runners at Perfect Stride Physical Therapy. “I’ve seen research show anywhere between 2–5 percent increase in cadence when you’re running on a treadmill.” This is a good thing; a quicker cadence and shorter stride are generally considered signs of healthier, more efficient running form. 

You can lock into a pace. Whether you set the treadmill to 4 or 7 mph, that’s the exact speed you’re going to run, Olivia points out. Zeroing in on specific paces can help beginner runners manage their effort level and help advanced athletes prep for races. It also lets injured runners return to the sport safely. “Putting them on a treadmill reins them in,” Sharma says, adding that, outdoors, it’s all too easy to push your pace without realizing it. 

You can set the exact incline. If you want to do a hill workout with a precise five percent grade, a treadmill will let you do that without having to hunt down the perfect hill. Sharma also takes advantage of the treadmill’s consistent incline for runners dealing with knee pain: “Research has shown that you can reduce your knee joint loads by up to 37 percent by playing with the incline on the treadmill,” he says. Alternatively, serious runners can mimic the elevation profile of a race to prepare for the exact course, no matter how far they live from the start line. For example, you can run the TCS New York City Marathon course via a Scenic class on the Peloton Tread or Tread+, and the auto-incline feature will match the elevation changes of the race.

You can avoid the elements. Whether you’re walking or running, rain, snow, sunburns, and heat exhaustion simply aren’t factors you need to worry about when you hop on a treadmill.

It can be more meditative. “Running on the Tread gives you the chance to turn inwards,” Olivia says. “You don’t have to navigate your surroundings, so you’re able to turn your brain off to fully be present in the work you’re doing.”  

You can run at any time. Is it too dark outdoors to safely run alone? Or is the temperature too hot to run comfortably during your lunch break? These simply aren’t issues you have to deal with on a treadmill, Olivia says, which means you can fit in your run whenever it works for your schedule. 

You get entertainment options. If you find running boring, a premium treadmill like the Peloton Tread or Tread+ will give you access to a whole bunch of ways to distract your mind: You can take instructor-led classes, watch live and on-demand shows, virtually run through scenic destinations, or compete against your past high scores with games like Peloton Lanebreak.  

You might get sweatier. Since you’re running in one place, the air isn’t moving around you (unless you have a fan on). As a result, you might find you heat up faster on a treadmill. 

It can put more demand on your Achilles. While the extra shock absorption can reduce the impact on your bones and joints, research has shown that treadmill runs can put more strain on the Achilles tendon than running outside. This is likely because runners typically take shorter strides on a treadmill, which, while healthier overall, can increase the load on this tendon, Sharma says. “When people are recovering from an Achilles or a calf or ankle injury, I may actually not want those folks to get on the treadmill,” he says. 

It can get monotonous. Unless you tap into entertainment options or mix it up with different types of treadmill workouts, things can start to feel stale on a treadmill, since your physical surroundings don't change. 

You get a harder workout at the same pace. Since you don’t have a belt continuously moving your feet backwards each time you land (like you would on a treadmill), your glutes and hamstrings have to work harder outdoors, Olivia says. “When running outside, you have to push off and propel yourself forward, working more muscles in your back body,” she says. At the same time, the uneven terrain on a trail or sidewalk gives your stabilizer muscles an extra challenge to keep you upright, she adds. (Note: These differences can sometimes make it feel challenging to transition to outdoor runs if you’re used to always running on a treadmill.)

Outdoor runs can be mood-boosting adventures. There’s some evidence that exercising outside can relieve stress more than indoor workouts can. “Running outside gives your brain natural stimuli,” Olivia says. “It can be more dynamic in terms of terrain as well as more visually dynamic, depending on where you’re running.” You can even turn outdoor runs into fun adventures by heading to a new neighborhood or out to some scenic trails in nature. 

Wind can both challenge and cool you. Outside, you’re moving forward through space, which creates some air resistance even on the stillest days. And if it’s windy out, you’ll probably feel it. “Even a light breeze outside makes your body work a little harder to push forward,” Olivia says. This also has an immediate payoff, though: “It helps with staying cool,” she adds. 

You learn to get a feel for different paces. Outdoors, you’re constantly adjusting your pace based on the terrain and your energy levels. “There is more trust and intuition involved internally and externally,” Olivia says. You learn to listen to your body’s cues to tell how fast you’re running, and adapt to changing demands.

You’ll build mental resilience for race day. If you’re training for a race, it’s smart to get ready for whatever the elements throw at you. “Running outside has natural weather factors such as rain, wind, sunlight, and different temperatures,” Olivia points out. Tackling these regularly helps you figure out the gear—and mindset—you’ll need if you don’t get ideal conditions on race day. 

You can disconnect from tech. Outdoor runs can offer one of the few chances we have these days to take a break from technology. Even if you're following a guided running workout, such as the audio-only outdoor running classes on the Peloton App, you can still practice mindfulness during your run by setting your phone and fitness tracker to “do not disturb.”

You have to carry your own fuel and hydration. Unless you map out a route that passes plenty of water fountains, you’ll likely need to find a way to bring your water with you on long outdoor runs. The same goes for fuel. That probably means carrying a water bottle, and/or wearing a hydration vest or running belt. 

Bathrooms can be hard to come by. You might not always have a toilet nearby when you need it. “Bathroom and water breaks need to be more planned out when running outside,” Olivia says.  

You need more gear. To run outside in all seasons, you’ll have to invest in more gear, like running gloves, ventilated jackets, UV-protective and waterproof layers, hats, and more. “With running outside, your gear will depend on the weather as opposed to it not being a factor on a tread,” Olivia says. 

Safety is a concern. You always need to be aware of your surroundings outdoors. When running on roads, it’s important to look out for cars, while on most trails, you have to keep an ear open for animals. Either way, running alone can be a concern, particularly after dark and particularly for women.