Repeated bodyweight lifts against gravity, disguised as a cardio machine.
Every step on a stair climber means lifting your full body weight upward against gravity, over and over. Unlike walking on flat ground, there's no momentum carrying you forward between steps — each one is its own small lift, which is why the MET value sits close to running.
At 8.8 MET, the stair climber outpaces moderate cycling and most gym cardio machines for calorie burn per minute.