I understand that you're challenging results to be sure they're reliable, but I think you're maybe going a bit too far. Is there any proof that "thoughts" or mental stress can have any impact on that type of tests?
Suppose you consider something like a panic attack. Now I'm one of the most laid-back people you will meet, but I remember being in the shower a few years back, and the postman came with a registered letter to do with my brother-in-law's estate. My wife signed for it, but I remember suddenly my heart was pounding like mad, feeling dizzy, in turmoil etc. There was no particular reason - I was a joint executor with a solicitor, and it was all pretty straightforward.
Now were the very real effects of my (mild) panic attack down to a mental response, or to a physical condition? I guess it would be really hard to sort out the borders there – do I have a chemical imbalance that now makes me more sensitive? Or had my illness changed my mental state? Just because an effect is clearly physical doesn't make it easy to get behind it and decide what the trigger is.
Now for the even more weird part, that was my one panic attack. I haven't had one before, and haven't since.
So, back to muscles, do they ache after a minimum amount of exercise because of some physical imbalance, because they have not been used for more than a certain amount, or because my mental state sends my physical system out of kilter when I do exercise? Do I have a similar kind of mental panic reaction when threatened with exercise, that affects the way that my muscles respond?
As you know, I am quite sure that it isn't my mental state or that I am out of condition, but that's not the same as being able to prove it. The psychs that believe ME is psychological (and remember that there are very many who do not) have been unable to show that they are right, and they have had the bigger share of research funding, so that is one argument that tilts the balance in our favour, but that's all it is. Until there is a clear-cut biomedical finding (as opposed to groups of different spreads of abnormalities), we can only argue in terms of a balance of likelihoods.
In fact, I don't think the psychs have ever really bothered much about trying to show the cause is psychological. Like a fervent fundamental religious adherent, they know they are right: it is clear from the way that the PACE trial was set up that all they intended to do was to determine whether CBT or GET was the better or the most cost-effective treatment.
But this balance is important when we are considering something like GET, which shows no advantages, and where the biomedical understanding suggests harm.