Stair climbers require you to walk uphill, just like walking stairs. This makes it more challenging than a treadmill while cutting out the jarring and repetitive impact of running. The stair climber would be a better cardio machine option for those recovering from injuries or with pre-existing joint pain. Treadmills on the other hand are a great cardio machine for people who don’t experience any issues with running and want to increase their aerobic capacity.