Is the treadmill harder or easier than running outdoors? Survey runners, and you’ll get plenty of different opinions on which feels harder or easier, but the basic physics of running are the same on both. (I promise.) So why do people who are used to treadmills find that they’re slower when they run outdoors? I’m going to run through the factors that are at play here, and talk about how to adapt if you want to be able to enjoy both. If you find treadmill running harder, you probably already know the reason: it’s boring. You have nothing to distract you from your own effort and the glowing numbers telling you how little progress you’ve made. This is a problem that we can train our brains to solve for us over time, whether with distractions, mindfulness, or simply being grateful that we’re not outdoors in the bad weather. For those who find treadmill running easier, the biggest reasons have to do with the environment (heat, hills, etc.) and with your mindset (especially your ability to pace yourself). Training both indoors and outdoors will help you to make the transition a little easier. Let’s dig into the reasons. The treadmill is not literally easierBefore we get into the relevant factors, I want to dispel a few myths. Physics-wise, running on a treadmill is pretty much identical to running outdoors in the same conditions.The treadmill does not move your feetThe first myth we need to bust is the idea that the treadmill “moves your feet” and thus makes running easier. That’s not true. You have to spend just as much effort to stay in place on a treadmill going (say) say 6.0 miles per hour, as you do to move forward at 6.0 miles per hour on flat, steady ground. Running is the action of pushing off the ground to move yourself forward. In both scenarios, you are asking your muscles to push off with a force that will keep you moving 6 mph faster than the ground. (If the “treadmill moves your feet” theory were correct, would we not have to consider the rotating Earth its own sort of treadmill? And thus it would be 2,000 times harder to run west than to run east? Come on.)You only need to add a 1% incline if you are running very fastThen there’s the issue of wind resistance. Some runners will say you need to set the treadmill’s incline to 0.5% or 1% to mimic outdoor air resistance. Even on a calm day, your body has to push into the air to keep moving. Adding a small incline to the treadmill is supposed to mimic that extra effort.But that is only true if you run at a pace of 7:30 per mile (8.0 mph) or faster. Below that, “the difference is so small as to be meaningless,” a scientist who studied the question told Runner’s World. So if you’re jogging at 6 mph, you don’t have to worry about accounting for wind resistance. Now that we understand the physics, let’s talk about why treadmill runs often feel easier than outdoor runs. PacingThis is probably the biggest factor (aside from weather) in why outdoor running feels harder for a person who is used to treadmill running. On the treadmill, you decide on a pace—say 6 mph, as in our example above—and then your body knows what to do. But outdoors, you just have to run, and then figure out later what pace you’re going. Even if you have a watch that tells you your pace, it takes a few seconds to minutes to work out what that number is. (You also may not be used to reading minutes-per-mile pace if you’re used to seeing mph on the treadmill, which makes it even harder to know how fast you’re going.) So you, the treadmill runner, head off on an outdoor run without a good sense of how fast you’re going. Perhaps you end up going a little too fast, but you don’t realize it until it’s too late and you’re pooped. Meanwhile, outdoor runners will develop a sense of pace out of necessity. You have to listen to your body, not just look at a number, to know how hard you’re pushing. The good news is that it’s easy for treadmill runners to learn a sense of pace—all you have to do is run outside from time to time. You’ll learn what your body feels like when you’re going at an easy pace versus a harder pace versus an unsustainable one. It just takes a little practice.Heat, humidity, and other weather conditionsIf all your treadmill runs are inside of a 68-degree gym, they’ll all feel pretty similar. But the great outdoors is fond of blessing us with heat, wind, humidity, rain, snow, ice, and similar complications. Heat slows us down a lot, especially if we aren’t used to it. (You do build up some heat adaptation throughout the summer.) Humidity, in combination with heat, makes this even worse. Your body can’t cool itself as well through sweating, so you get hot and stay hot. It’s normal for your pace on a hot day to be anywhere from a few seconds to a few minutes slower each mile. Heavy winds can also slow you down (when you’re running into the wind) or speed you up (when you’re running with the wind at your back). Ice can make you slow down to watch your footing. Snow can make you work harder as your feet sink into the ground and you have to fight to pull them back up again. On the other hand, a cool, dry day is better for your performance than the conditions inside a sweaty gym. Perfect running weather is (in my opinion) around 50 degrees, calm, and overcast. Most people will run a lot faster and feel better in those conditions than on a treadmill at room temperature.HillsIf you live in a pancake-flat part of the country, you can skip this section. But many of us live where there are hills. Big ones, little ones, maybe some mountains. On the treadmill, you get to choose what incline to run with. Outdoors, your choices may be limited. I live in a hilly place, so even my “flat” outdoor routes aren’t entirely flat. A regulation running track is my only truly flat option. Even gently rolling hills can add up over the course of a long run, making you work harder on the uphills without ever fully giving you that speed back on the downhills. Different surfacesA treadmill only has one surface. Every step meets flat ground. Every step is the same softness or hardness. Outdoors, there’s so much more variation. Even on a simple city run, you’ll find yourself traversing curbs, slightly tilted sidewalk slabs, cambered edges of roads, pebbles, stray garbage, and occasional patches of grass or dirt. Take your run to the trails and you’ll also hit packed dirt, mud, soft grass, leaf litter, rocks, sticks, logs, little streams you have to hop over, ruts carved by mountain bike wheels—you get the idea. Your feet have to land and push off just a little differently for each of these. The variety in outdoor running is good for your feet, but it can be fatiguing on the small muscles of your feet and lower legs if you’re not used to it. How to train for an outdoor race if you prefer to run on the treadmillIt’s OK to do plenty of your training on a treadmill, and in some situations it may be necessary. The treadmill can let you get your training in when the weather is bad, when you can’t line up child care at your running times, or any of a number of other reasons. The important thing is to still run outdoors at least sometimes. If you’re training for a marathon, try to do your long runs outdoors, even if some of your shorter runs and speedwork have to be on the treadmill. Get outside when you can. That way you’re adapting to the weather, training your feet on different surfaces, and building the muscles and mindset necessary to tackle hills.