The Arc Trainer is a piece of cardio equipment produced by Cybex International. The design simulates running, but you stand on independent pedals that swing in a crescent pattern. This motion makes sure your joints don't incur impact as they would on a treadmill. According to Cybex, you burn 16 percent more calories using an Arc Trainer than a standard elliptical trainer, and your body moves in an optimal path. You'll also experience less stress on your joints than you might when running on a treadmill.
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When to Use
If your goal is to build cardio fitness, an Arc Trainer and a treadmill can both help you reach your goals. You might choose an arc trainer over a treadmill if you have knee, ankle or back problems. An Arc Trainer is not a replacement for running on a treadmill if you preparing for an event that involves running, though. It is useful for cross training -- to maintain cardiovascular fitness and challenge your muscles in a slightly different way -- but it won't get you ready for a road race.