Q: Just how accurate are those “calories burned” numbers?

Longer answer: Treadmills fool us by estimating total calories burned during our time on the machine rather than the net number—i.e., calories burned solely through exercise, above and beyond what we would have used anyway. (We all burn a certain number of calories even at rest.) Here are some simple equations to calculate and compare total calories burned per mile versus net:

For running (5 mph and higher): Total calories burned per mile = .75 x body weight (in pounds); net calories burned per mile = .63 x weight.
For walking (3 to 4 mph): Total calories burned per mile = .53 x body weight; net calories burned per mile = .30 x weight.

Q: Is treadmill running easier than running at the same speed outdoors?

Longer answer: Treadmill running may feel more taxing, but physiologically it’s actually a bit easier than running outdoors. In his book Treadmill Training for Runners, Rick Morris explains, “Running on the treadmill, you don’t have to overcome the effects of wind resistance and you also have that assistance of a moving belt doing part of the work for you.” To more closely simulate road running, set your treadmill’s incline at one or two percent.

Longer answer: You can train for a road race mostly on a treadmill, says Jenny Hadfield, coauthor of Running for Mortals and Marathoning for Mortals and a runnersworld.com columnist. But you’ll have to make a few tweaks. For starters, be sure to increase the incline and run “hills” on the treadmill once or twice a week. And because treadmill belts offer a relatively soft landing, take steps to prepare your body for racing on asphalt:

• Strength-train twice a week (lunges, squats, hip extensions, planks, push-ups).
• Do at least one short outdoor run each week during the last four weeks of training.
• During your race, walk a minute at every mile marker or aid station. This will ease the overall impact on your body and give you a chance to hydrate.
• Finally, on race day, run by effort—not by pace or time goals. You’ll be on unfamiliar ground, literally.

Q: Should I wear different shoes on the treadmill?

Longer answer: “Most runners wear the same shoes whether running inside or out,” says Runner’s World shoes and gear editor Jeff Dengate. If anything, Dengate says, treadmill runners might opt for a lighter pair of shoes that offers less cushioning, because the treadmill’s running surface is softer than most outdoor surfaces. That said, if you wear a shoe with any motion-control features, choose something similar for the treadmill to be sure you have the proper support.

Longer answer: In general, running on a treadmill is less stressful on the body than running outdoors. John Post, the medical director for TrainingBible Coaching, explains that the treadmill absorbs a significant amount of impact, sparing your body. On the other hand, he says, “The downside is that it doesn’t condition the shock-absorbing musculature of the lower extremities like road running does.” Result: Over the long term, heavy treadmill use may actually leave you more prone to injuries like stress fractures.

Q: Why do treadmills use “mph” when runners prefer minutes per mile?

Short answer: Because mph is beginner-friendly.
Longer answer: Most treadmills offer both readings of miles per hour and minutes per mile. Manufacturers include mph because beginners or casual treadmill users may not be familiar with the concept of minutes per mile, which is the measure preferred by experienced runners.

If you’re stuck on an old treadmill that offers only mph, converting to minutes per mile just requires some math. Here is a cheat sheet:

Miles per Hour Minutes per Mile
5.0 12:00
6.0 10:00
7.0 8:34
8.0 7:30
9.0 6:40
10.0 6:00
11.0 5:27
12.0 5:00

Q: Am I better off running faster with no incline, or slower with a steeper incline?