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You probably know all about motorized treadmills from the gym. But here’s the lowdown on three other types—and what they’re best for.

Whether it’s frigid or sweltering, whether you’re a gym addict or looking to switch it up from your current workout routine, you may find yourself in need of a treadmill. But all treadmills are not created alike. In fact, in addition to the traditional motorized version you’re likely to see at the gym, there are manual treadmills, curve treadmills, and anti-gravity treadmills, each of which is suited to different kinds of workouts and different sorts of runners. Which ’mill is right for you? Here’s the lowdown: 

The manual treadmill is a treadmill in its simplest form: activated by running and deactivated by stopping. In general, because of its simplicity and lack of motor, this type of ‘mill is less expensive than its motorized counterpart––and safer. Controlling your pace is easier, too, but in some respects manual treadmills can be more difficult to use, as your stride needs to be consistent and fatigue sets in more quickly. And if you want to adjust the incline to increase the intensity of your workout, well, you have to hop off and do so manually. There are a wide variety of reasonably priced manual treadmill options to choose from, and some even fold up for easy transportation.

Check out our review of the Trueform Runner manual treadmill, a perfect fit for competitive racers.

The curve treadmill is a manual treadmill that, yup, has a curved surface: You run in the bottom of an arc. Gravity plays neat tricks here. Stepping farther up the arc speeds you up, while stepping farther down slows you down—all of which requires better form and greater control over your gait. That makes curve treadmills excellent for both consistently paced runs and interval training. (In fact, because you can start and stop so easily, curve treadmills are good for intervals with a buddy: While you run, your friend rests, then you switch places.) At Runner’s World, we like the Woodway Curve Trainer and the Trueform Runner.

The Woodway Curve Trainer helps hone your proper running form.

The anti-gravity treadmill has been a game-changer for physical therapy. It works by zipping your waist into a plastic-sealed bubble that surrounds the base of this motorized treadmill. Once you’re in the bubble, you can reduce gravity’s impact to as low as 20 percent of your body weight, thereby reducing stress on joints and injured areas of your lower body—while maintaining a normal gait. If an injury has forced you to take time off from running, this treadmill is a great way to get back into it. They can cost a hefty $75,000, though, so unless you’re feeling flush (contact Alter-G if you are!), you’ll probably find an anti-gravity treadmill at a physical therapist or a running clinic.