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 exert

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.