I have wrestled with the question, did people who recover with GET ever have ME/CFS in the first, is it ever possible for gentle exercise to somehow help "genuine" ME/CFS in some cases? I don't know for certain, but it sounds suspicious. CFS is poorly defined, effectively a wastebasket in practice, and often bandied around without medical diagnosis even in research. Therefore it is highly improbable that all these people have the same condition or illness characteristics, even if they meet a medical diagnosis for CFS.
Meeting vague CFS criteria known to have sensitivity/specificity issues and then experiencing benefit from GET is not identical to having the same condition as those who meet CFS criteria but do not experience benefit from exercise and are instead worsened by it. Patients and advocates are accused of the "no true Scotsman" fallacy when stating those who recovered from GET (and CBT) never had "real" ME/CFS in the first place. However, unlike what haggis is to being born in Scotland, becoming worse after exercise has been argued to be a fundamental criterion for ME/CFS (although not a requirement for most CFS criteria).
A counter-argument to that would be, post-exertional symptoms are just from deconditioning and/or chronic stress and/or even people reporting "PEM" still gain benefit from GET regardless. However, these models have never been proven, and descriptions of post-exertional symptoms differ enough to influence reported prevalence. For example, in the revised Canadian definition by Jason et al (
http://www.scipub.org/fulltext/ajbb/ajbb62120-135.pdf) it states: "
Within a group of individuals diagnosed with CFS, Jason et al. (1999a) found that post-exertional fatigue or malaise for individuals with CFS ranged from 93.8-40.6% depending on how the question was asked. There is certainly a need to standardize the questions used to reduce this source of unreliability. In addition, length of the period of post-exertional malaise may vary from activity to activity or by time period within the person."
Although post-exertional symptoms and being unable to experience benefit from GET are not necessarily the same either, judging from many patients' experiences (outside the stranglehold of proponents publications) it effectively is the same because the activity ceiling is absolutely real and cannot be evaded by GET, the piper has to be paid eventually. If you can evade your limitations with GET, perhaps you're recovering anyway or your illness does not have the same characteristics of others who can't maintain GET. I can see how exercise could be useful for regaining fitness levels during underlying recovery, but otherwise is useless and dangerous. As we see in GET studies using a control group eg attempting GET coincides with natural improvements, most of the PACE GET group who reported improvements and being "within normal range" (cough) would have done so anyway. I guess it is also possible for a grey area to exist where some mildly affected genuine patients have over-compensated to their symptoms and are operating far below their activity ceiling?
Considering patients' negative experiences including my own, I did not fully understand how "scientific" GET studies usually reported to be "safe" without adverse effects despite the presumed increase in activity until I realised that increases in activity during such studies was not actually mandatory. There is no convincing evidence that patients are generally increasing their overall activity levels after GET, it is merely presumed that they are. This presumption when combined with rigid real world applications of GET is dangerous. Peter White claims that reports of adverse effects in GET from patient surveys is probably due to rigid forms of GET rather than fundamental problems with the approach of GET. The irony though is that White's supposed caution makes it possible for patients to report improvements after GET for reasons other than exercise and without actually increasing activity level.
It is highly suspicious that the king of all GET trials the PACE Trial that White lead decided to drop the main objective outcome measurements of physical activity! Another issue is with how an adverse effect in defined. In the PACE Trial is was possible to become bedridden for up to 4 weeks due to GET and for this to be considered a non-significant impact on function! I bet the people who reported adverse effects from GET in patient surveys have a different idea of what can be described as an adverse effect.
Anyway, in my own experience over many years, I have tried different approaches to exercise and GET but all failed no matter how careful I was, there is something fundamentally wrong about the approach for me. At first I figured this is just one person's experience so perhaps other people experienced benefits just like GET studies indicate. But over time it became more clear that so many other patients have the same problem as me and the research into GET is flawed. So I have gone from totally accepting the notion that GET can help, to, wondering whether it is some delusional fad pushed inappropriately on people with CCC-ME/CFS. The main "expert" proponents of GET are still making n00b mistakes after 20 years like assuming PEM is just normal delayed onset muscle soreness that healthy people experience, yet these n00bs are influencing world opinion on ME/CFS!
The state of knowledge on ME/CFS is currently not much beyond the same stage Parkinson's disease was at when psychiatrists were proposing that the tremors were due to the struggle to control the overwhelming urge to masturbate. Maybe in the future there will be lab tests to help distinguish between those ME/CFS patients who are helped and those who are harmed by increasing activity levels. It would be interesting if "cannot be overcome by GET" were to become an official ME/CFS criterion.