Traditional treadmills have a flat surface that doesn't offer much in terms of challenging your body. But curved treadmills are a different story. The gentle curve of the treadmill forces your body to work a little harder as you walk or run, and this can have a big impact on your calorie burn. In fact, research has shown that curved treadmills can helpnnyou burn up to 10% more calories than flat treadmills. So if you're looking for a treadmill that will help you torch more calories, a curved treadmill is the way to go.