As you know, the etiology of these conditions are not really known. I include M.S. in this group. I have studied and worked with a number of cases. Since all these conditions have joint and, muscle pain discomfort , I tend to use exercises that focus on increasing the strength of the muscle at the joint. I use isometrics as tolerated ( gentle at first) to complete this task. As , the muscle near the joint becomes stronger, I work them slowly into a low impact aerobic activity. Since many individuals with the conditions above have good and bad days, progress is slow. they need much encouragement. Hope this helps!