Certainly it is very paradigm-challenging to learn that the thing that works to remediate some other conditions causes harm in the context of this one.
I think Mike Godwin is showing his lack of expertise here a bit. Just because the daily papers keep banging on about exercise being good for us there are all sorts of conditions made worse by exercise. Septic arthritis, hypertrophic obstructive cardiomyopathy and aortic stenosis (sudden death in those), sickle cell anaemia, altitude sickness, osteogenesis imperfecta, leprosy, ... in various ways scores of conditions.
And for people with motor neuron disease or muscular dystrophy you get nowhere by sending them to the gym because it makes no difference. They try as hard as they can all day long.
And everyone keeps forgetting that PWME do not actually need to exercise - they are not severely deconditioned as a whole. What they need is to be able to do ordinary activities without distress, not run marathons for the sake of it.