@ggingues, microcirculation keeps coming up. Its one of the possibilities that has to be investigated. Yet it might only apply to a subgroup. We need lots more research on this. In post exercise responses, a huge percentage of strictly defined CFS patients have a fibro-like response, but a big percentage don't too, according to the Light's research - or at least as far as I recall, it might be time I went back and reread that research. Something is stopping the electron transport chain from doing its work. There are a number of plausible candidates. What needs to be considered is nutrient supply (substrate, including oxygen), waste removal (including oxidative products) and regulation (including enzymatic capacity). In us all three appear to be compromised. Indeed, it might turn out to be a combination problem.