I was wondering how useful this type of testing has been to people. I've been using a heart rate monitor and based on the 220-age x .6 formula worked on keeping my hr under the estimated threshold. I have been actually having more PEM so I'm guessing my estimation of my threshold is wrong. For those who've had actual testing done, has it helped you avoid or reduce PEM by staying within your threshold? Also, as far as testing goes, does AT get affected by PEM? So if you test on a good day and do not do a second day test, will your AT not be totally accurate on days when you are already under the effects of previous exertion? In other words, is it necessary to do a test two days in a row or is one sufficient/accurate enough for those with CFS/ME? And one more sort of related question: Would this kind of exercise stress test prove useful for those with CFS (who don't suspect coronary artery disease)? http://www.heartsite.com/html/regular_stress.html The info on the test says it can help evaluate exercise tolerance when patients have unexplained fatigue and shortness of breath. I'm not sure what is evaluated exactly. I can ask my doctor about this, but I just wondered if anyone may have any insight or done this type of test before. Thank you.