Consider the machine's speed and incline. The top speed on the models we tested ranged from 7 miles per hour to 12 mph with inclines ranging between a low of 5.5 percent to a high of 15 percent. Look for machines with programs that allow you to adjust routines based on your fitness level and have heart-rate-controlled workouts that consider your age, weight, and gender.
Look for a display that can easily be read and large controls that are logically presented. Remember, you'll be reading the statistics and accessing the controls while you're moving. A good display will show some combination of your heart rate, calories burned, speed, and incline levels, and details such as time and distance.
Gadgets, such as MP3 docks with speakers or a headphone jack, or LCD TVS, don't have much effect on performance. But if they entice you onto the treadmill, they might be worth your while. Newer features, such as USB workout trackers or virtual trainers, might inspire you to intensify your workout. Some users might find the lack of a magazine rack or water-bottle holder to be a nuisance.
Those with a chest-strap heart-rate monitor are best because they don't impede your movement. Contact monitors measure your heart rate only when you're holding onto them, which can impede your natural stride. But it doesn't need to be a deal-breaker; stand-alone heart-rate monitors are available for about $35 to $110. If however, heart-rate programs that automatically adjust the speed or incline settings are one of the machine's features, it would be most convenient if you didn't have to hold onto the machine.
Look for a machine that is easy to adjust and has a variety of workout levels. Treadmills offer a range of speeds and inclines. Some can simulate running or walking downhill.