A thick deck. The platform on which you'll run or walk is the machine's deck. A deck that's at least three-quarters of an inch thick will stand up best to the impact of running. If you're short of space, look for a deck that folds up. Make sure you can lift the deck easily and that the latch holds it securely in place.
Wide foot rails.
Foot rails are located on either side of the deck. Make sure you can stand on them while you start up the treadmill and that they're not tilted or wobbly. Look for a belt that's at least 17 inches wide and 51 inches long. A small belt increases your chances of stepping off accidentally when it's moving. They should be close enough to reach if necessary, but they should not get in the way of your swinging arms.