<human>: What is the difference between a treadmill and a stair climber?
<bot>: The main difference between a treadmill and a stair climber is that a treadmill requires you to walk or run on it, while a stair climber allows you to move up and down stairs without having to run. Treadmills are generally stationary and require you to be in place as you exercise, whereas stair climbers can be used anywhere.