5. A mental challenge. Slogging through the miles without any change in scenery (except maybe the person next to you in the gym) can be mind-numbing. It's great mental training—especially useful for long, tough races—learning how to suck it up and deal with it.
If zoning out just isn't your style, then keep yourself busy. Try, for instance, to get your heart rate to the top of zone two or three and then see what you have to do to bring it back down again. See how many times you can bring it up and down in 20 minutes while running on the treadmill.
Or just be glad you're not aiming to break the world record for most miles run on a treadmill at once (currently confirmed at 153.76 miles, although there's an unconfirmed challenger who may have topped that).
6. Data. "I'm a geek and I like numbers," Cane says. "You know exactly how far you've gone, how much you've climbed, and so on. Pair your workout with a heart rate monitor and duplicate a specific workout periodically. It's a great way to gauge your progress."
In the end, running on the treadmill isn't so bad. Take your treadmill training to the next level and reap the benefits.race.