I wrote all this is a post on another thread, but decided it was a bit OT, so here it is an a new thread instead for those who want to know what it's like. Hopefully others will add their experiences, positive and negative, to help patients make the decision about whether (and how) they want to do it. I've done exercise testing twice now. Once about 4 months after my diagnosis (3 years after the sudden onset viral illness that was my trigger). At that time I was still trying to behave "normally" and going through push-crash cycles. The second time was 4.5 years later (about 1.5 years ago) after Valcyte and Valtrex treatment. I felt hugely better, but was still extremely limited physically and was using my previously determined AT to manage my activity. I was hoping my AT would be higher so that I could do more without exceeding it (and thereby inducing a crash). It wasn't any higher. Not a bit. Exactly the same. What follows is my assessment of the value of exercise testing to patients. I think that activity management based on AT may improve outcome in some current treatment modalities. Some, if not all, current medications (including supplements) may not be as effective if the patient continues to stress the system. Or perhaps the body can't heal even if, for example, a pathogen has been eliminated. Appropriate rest while minimizing deconditioning with excessive rest is advised in all serious illnesses. The issue is what is appropriate rest for us. My guess is that it is a LOT more rest than most of us are getting. I had made what I felt was a huge reduction in my activity -- maybe 50% -- when I got ill. After AT testing I realized I had to go down to about 10-15% of my previous activity level to stay below my AT. It was only then that I (mostly) stopped having crashes and getting slowly worse. Eliminating most of the crashes (I can still crash from an infection) was a big benefit to me. My baseline was getting a little bit worse after each crash. After limiting my activity according to my AT, and thereby severely reducing the number of crashes, I stopped getting worse, and maybe started getting a tiny bit better. With various treatments I've been able to increase that 10-15% to somewhere about 60-70% and heading upwards rapidly. However, during some treatments (Valcyte in particular) and infections/vaccinations, I've had to back down a bit in my activity level to stay below my AT. I wouldn't have known this if I didn't have my AT info to work with. This could be just me, of course. I tend to be a data-driven person, and not the best at understanding my body -- and my body's not the best at communicating with me, either. A high pain threshold and a remarkable physiological capability to cope with adverse conditions, while great for a Navy SEAL in a crisis, is not the best for judging general health in the long-term. So having data to work with -- don't go over this number even if you feel capable of continuing -- makes it possible for me to manage my activity correctly. I suspect a lot of us do more than we should be doing, though, not just me. I see a current place for exercise testing in ME/CFS treatment. I think Dr Sol's choice to test to AT rather than max capability is the wiser choice for routine use. I think most (not all) of us could do her test and gain highly useful information without serious adverse consequences. The first time I did exercise testing, I was tested to max. I got off the bike wheezing, near vomiting, and ready to pass out. I crashed several days later. Big PENE attack. Not fun. But ultimately useful enough I was willing to do it again 5 years later at Dr Rey's office to see if my AT had changed after aggressive antiviral treatment (It hadn't). The second test (Dr Sol's) was really, really easy -- sitting on a bike and waving my legs around. I can hardly even call it pedaling. There was no resistance (that I could feel). This went on a few minutes (less than 10, I believe) until I reached my AT, when we quit. ( Ummmm..... yeah, I actually threw up afterwards, but it wasn't the test, it was food poisoning -- my husband had it, too. Don't eat in Mexican restaurants near the airport in Miami. ) No wheezing, no crash, easy peasy -- and at that point I was still in a wheelchair for any distance over 30-50 ft [10-20 m for you sensible metric users]. Unfortunately, I didn't get any new information from the second test. Neither doc said so outright, but my impression is that they didn't/don't expect my abnormally low AT to change, even as I get better. I don't believe there is any research on that topic, though. What has changed for me is that I can now do more without exceeding my AT.