Hi! I have read several medical research papers that have run something called test-retest studies on 'normals' and on ME patients. Basically, cardiac function and muscle function are tested...the patient is exercised, then given 24 hours rest. Then the original tests are run for a second time. The 'normals' get the same scores on their tests as they did the first time. But the ME people test significantly worse on the second test -- because their bodies have not recovered from the exercise. I have also seen cognitive function tests like this too and again, patients with ME show a decline in cognitive functioning after the exercise and rest. During rest, normals recuperate -- but ME's recuperate so much more slowly. I myself know that once I get the extreme pain and weakness in my legs, if I have to keep going, I wll get so weak that I can not get up stairs: I put my foot on the step, and push on my leg...but nothing much happens! I have to basically haul myself up by the hand rail. Yet, when I am stable (which, thank God, is most of the time now) I am able to walk my dog, garden, shop etc. But that old leg issue still makes me crash (or is part of a crash) and I end up in bed from time to time for a few days, waiting for my strength to recover. I'm sorry I can't remember where I read those papers; likely on the prohealth.com site, in the library section.