There is something akin to a daily exertion limit in CFS. When patients exceed it, they have a relapse. It is very easy to have these relapses because the exertion limit is so low.
There must be a biological mechanism behind this limitation. It could be something to do with energy generation in cells and this test may be measuring the associated impairment.
I have some doubts that this will be 100% specific to CFS, but as professor Davis said at this point it's important to demonstrate that these patients have something wrong with them.
Davis called this the last major disease we know almost nothing about. It's 2-3 as common as multiple sclerosis with worse impact on the person's life. It's also the most underfunded illness when the number of patients and the severity is taken into account.
There is no dangerous CFS militant movement that threatens to kill psychiatrists. There are just some psychiatrists who can't handle criticism and get their journalist friends to write these smear articles in the hopes it will silence their critics.