So basically, something is causing metabolic changes which impair exercise and trigger fatigue and painful muscle inflammation which then triggers avoidance behavior.
So the problem here is probably that you need to do the test after sufficient exertion.
The Myhill group detailed a very interesting mechanism by which they propose mitochondrial blockages lead to PEM — a mechanism is described in
this post. I think irrespective of whether the Acumen lab tests are valid or not, this theorized mechanism may still be a viable explanation for PEM.
If you look at this Myhill PEM theory, you realize that the mitochondrial blockages can be ever-present, but it is only when the body is pushed through higher levels of exertion do the consequences of those blockages appear — as PEM. But even without PEM occurring, the blockages are still there, and thus should be measurable in tests, according to this theory.
In brief, the Myhill PEM theory is this:
The ATP molecule can viewed like a wooden delivery cart that is stacked up with energy. When ATP delivers the energy into the cell, this wooden cart is then sent back to the mitochondria for recycling and refilling with energy. But if the mitochondria are blocked in any way, as is believed is the case in ME/CFS, this wooden cart refilling process becomes much slower. This blockage is not an issue when body energy expenditure is on tick-over, but becomes a problem when energy expenditure rates increase.
When energy expenditure is increased, ATP cannot be recycled quick enough (ie, the wooden carts cannot be refilled fast enough) to meet energy demands because of the blockage; but the body has a back-up system that can temporarily help out: this back-up system involves burning the wooden carts themselves to create energy!
This burning of the carts works fine in the short term, but the long term consequences are that you now have no wooden carts (ATP molecules) to delivery energy. And it is this that creates the PEM state, according to the Myhill group. It's only when the body makes some new wooden carts to carry energy do you get over PEM. But because it takes days to rebuild these wooden carts (rebuilding is called de novo synthesis of the ATP molecules), PEM itself often takes days to clear.
This is only a theory of PEM, it has not been empirically proven; but it is the only theory I have seen which can neatly account for how higher energy expenditure leads to PEM.
As I say, even if the Acumen lab "ATP Profiles" blood test is not correct, this theory of PEM may still turn out to be right.