I second what @
Mij says and like to add that an old friend of mine, who is into scientific research @ a very prestigious institute and used to run marathons for fundraising, says that running is not a healthy sport, on the contrary.
Even healthy people get hit by a storm of pro-inflammatory cytokines post marathons.
I bet that when PWME are in a viral/immunological flare up, will forcibly and naturally, be unable to sustain any physical effort, of any kind.