I would actually say, for those of us with a prodrome phase, step count may be one of the last things to crash? To be fair, I wasn't running marathons, but like
@DHagen and
@V.R.T. (if I'm remembering correctly), I *was* trying to jog my way out of it right up until I was properly disabled.
My sense is the prodrome phase involves a lot of feeling ill/awful, not responding normally to exercise, plus cognitive, brain fog and/or mood problems (not to mention various gut and other 'autonomic' things seemingly going a bit haywire). And yet at this point you are still trying to maintain a normal lifestyle with all the walking and exercise that entails.