The only time I can think of fat lazy people in a cart would have to be the McDonalds carts at DFW? They just shuttle you from McDonalds to your gate and vv. That's about as bad as it gets.

I sprained my ankle last year and I was fine walking level, but stairs/ramps going down would grind me to a halt. If you saw me walking around you wouldn't know, but going downstairs drove my ankle crazy.
...I never took the cart during that time, but darned if i'd actually move on the escalator. I would keep completely to the right though.