The SF-S2 Sprint Demon Curved Treadmill is Designed for HIIT Training (High Intensity Interval Training), Circuit Training, Sprints, Short Distances and Walking / Power Walking. Like running on air- burns up to 30% more calories than a motorized treadmill! Ultra-thin and flexible ...The SF-S2 Sprint Demon Curved Treadmill is Designed for HIIT Training (High Intensity Interval Training), Circuit Training, Sprints, Short Distances and Walking / Power Walking. Like running on air- burns up to 30% more calories than a motorized treadmill! Ultra-thin and flexible slats offer cloud absorption, which makes the SF-S2 Sprint Demon Treadmill extremely lightweight and promotes less stress on joints and more activation of muscles resulting in higher intensity workouts 7 Levels of Resistance: low resistance for sprinting, medium resistance for walking, high resistance for power walking/running while holding handrails (imitates sled push).