Is running on a treadmill as good as running outside?

Yes. For fitness, a treadmill run is about as good as running outside. Your heart, lungs and legs get the same kind of work. A couple of small differences matter if you're training for a race, but not much if you just want to be fit.

What's actually different

• Wind. Outdoors you push against air resistance, which costs a bit more energy. Setting the treadmill to a 1 percent incline roughly cancels it out.
• Surface. A treadmill belt is softer and more predictable than pavement, which is easier on your joints. It's also flat, so your stabilizing muscles and ankles work less than on a trail or a road with a camber.
• Pacing. The belt sets your speed, so you can't drift slower when it gets hard. Some people find that makes treadmill runs feel harder, and others find it makes them easier to stick to.
• Weather and safety. The treadmill wins on both.

When the treadmill is the better choice

Heat, ice, darkness, or just having a young kid asleep upstairs. If the choice is a treadmill run or no run, take the treadmill run. It's also good for controlled interval sessions, since you can set exact speeds.

Treadmill runs count too. In League of Fitness, workouts sync from Apple Health and are scored by heart rate zones, so what matters is the effort you put in and not where you ran.

When you should get outside

If you're training for a road race or trail event, do at least some of your runs outside, especially long ones. Hills, turns, uneven ground and the pacing judgment you need on race day don't come from a belt. Outdoor running also tends to feel more fun, which matters more than people admit.

A quick tip

Don't hold the handrails. It reduces the work you're doing and throws off your posture. If you need them to stay on, lower the speed.

The treadmill also makes a good starting place for people building up, because you can walk and run in intervals without worrying about how far from home you are. If you're brand new, see how far a beginner should run.