Does running three miles on the treadmill equal running three miles outdoors? -Tiffany, South Pasadena, CA
Not quite. "You're much better off hitting the trail or road," says running coach Denise Margulies, co-owner of Core Fitness, a private fitness center in New York City. Running against wind or on uneven terrain engages more of your muscles, requires more energy, and burns more calories (10 percent more, says Margulies).
If you can't get outside, do speed work on the treadmill (run hard for a minute, then jog for a minute, for a total of 30 minutes); the moving belt means less muscle power is required from your legs, allowing you to run faster. And set the incline to 2 percent to simulate an outdoor run more accurately.