Thanks Lesley. If I understand what you're saying, there's an assumption that the AT of ME/CFS sufferers is low, therefore the activity doesn't need to be all that intense by normal standards before the anaerobic system kicks in. I guess the theory is that the AT is low because the energy systems are damaged, rather than through deconditioning (or possibly a combination of the two?). So what they are saying is that (relatively) higher intensity activity for short durations is better than lower intensity activity for longer durations. Hmmm, still seems counter-intuitive to me, and because I'm not deconditioned by normal standards, i would have to do fairly intensive activity to get above AT. My experience tells me that I get PEM whichever way I do it, and higher intensity, even if for short durations seems to have more adverse effect on me than lower intensity. I need to read that paper propoerly. Sorry, this is not a very well thought out post (are they ever?).