This conversation is likely of interest to many here. I wrote it to @Valentijn because she previously expressed an interest in exercise testing. Hi @Valentijn, At one point you mentioned you were interested in what I learned at the Mitochondrial Conference. Dr. Rajeev Bhatia's presentation on "Exercising Testing in Mitochondrial Disorder -- Unmasking the Defect" was very interesting. Specifically, how exercise testing is used as a test to rule in or rule out mitochondrial myopathy and that it was also useful in monitoring therapy (such as Mito Cocktail supplements and medication trials). Dr. Rajeev Bhatia's study results reflect exactly what was recently found when our local pulmonologist did the exercise test on our 19 year old daughter. She did the bike test (but it can also be treadmill). They pinched her nose and had her breathe through a tube. They found her peak exercise capacity is reduced (with a maximum oxygen uptake, or VO2, of 61% of the predicted value for a healthy person of her age and size). In addition, there were additional abnormalities that are consistent with mitochondrial disease, including an early-onset anaerobic threshold, a somewhat overly brisk rise in her heart rate, and a borderline-low value of the peak oxygen pulse. All of the findings on my daughter matched with Dr. Rajeev's findings on his patients. They are sending my daughter for an echocardiogram to rule out any heart issues that can cause this. Otherwise, these results are just another indication that she has Mitochondrial Disease. We know the echocardiogram will come out fine since she has had these in the past. They will now be testing our entire MitoD family with the same exercise test. Since some of our symptoms are similar (yours and mine including exercise induced asthma), it's possible that such an exercise test could help determine if your Chronic Fatigue is also caused by Mitochondrial Disease. Not all mutations are known yet, but it looks like this CPET test along with ruling out heart issues is a strong indication of MitoD. Of course, MitoD can also cause heart issues, so having similar results to my daughter plus heart issues, does not necessarily rule out MitoD. Over and over again at the conference was the fact that many MitoD patients go from aerobic to anaerobic too quickly. Once in anaerobic, even the best athletes can only keep going for just a few minutes. Therefore, those of us who get winded doing dishes and walking up stairs and have to lay down to catch our breath -- it could be a mitochondrial issue.