^nobody who needs to walk with the aid of crutches can run on a treadmill,^
I've held back as long as i can, but this is bugging me so much I can't let it go, try as I might.
When I have had a bad back, I could only have walked with crutches. Despite that, I would have been capable of running on a treadmill. Admittedly, in my case there is a proviso - I would have to lean forward, holding on to the bar that (at the last gym I used, at least) you are meant to hold on to anyway. That doesn't mean that there aren't other disabilities where even that bar would not be needed,
My own intermittent back problems are fortunately few and far between and would never warrant my getting any benefit, but they are a very basic example of how even a very common complaint can explain this perceived anomily.
What exactly this has to do with the OP, I have long since forgotten, but as I said, this has been bugging me too much to let it go!