<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 is stationary, while a stair climber involves moving up and down stairs. A treadmill typically has a flat surface where you can walk or run on it, whereas a stair climber allows for more complex movements such as climbing stairs, jumping, and stepping up and down. Additionally, treadmills are usually designed to simulate walking or running at a certain speed, while stair climbers allow you to choose your own pace and intensity level.