Hi
physical inactivity causes deconditioning - however in ME I suspect deconditioning occurs by two processes, 1. lack of physical activity and 2. inflammation that damages cells, e.g. increased free radicals, lower ATP, and so on: I think Cardiovascular deconditioning is a major problem in ME. Pain is way more complex, and probably is only slightly related to deconditioning. We know exercise increases our tolerance to pain, thus the opposite might be true.
this is a controversial thing to say, but as an ME sufferer with severe ME, I find that the psychiatrists are right in one small way, that is, to just lay in bed doing nothing but resting will weaken you and staying home and being isolated will lead you to develop agoraphobia, perhaps depression and so on: thus in my view, we must move when ever possible, via what ever form of exercise we can do, I called mine "micro-movement" - if I have one hour in the day that I feel really well I do a few minutes on my exercise bike, or pick up light weights, if I am having a bad day it might just be going down stairs to pick up the post, or getting in and out of bed every hour or so.
but I am more and more aware of the vital need to move --- however I DO NOT agree with Graded Exercise as a therapy for me. GET is different, it is too unitary, has targets which I think is wrong, doesnt account for boom and bust, doesnt account for daily and hourly changes in symptoms, almost places responsibility on the patient, ie if goals are not met. Also its promoted as a treatment for ME, its not, its an adjunct part of ME management, it doesnt cure anyone. We need to find the underlying biological cause.