Comparing Idiopathic Chronic Fatigue and ME/CFS: Response to 2-day CPET, two papers males & females, 2021, Van Campen & Visser

Conclusion: This study confirms that female ME/CFS patients have a reduction in exercise capacity in response to a second day CPET. These results are similar to published results in female ME/CFS populations. Patients diagnosed with ICF show a different response on day 2, more similar to sedentary and healthy controls.

The studies confirming this basic pattern are stacking up. We are way past the point now where anybody can say it isn't a thing, that they couldn't have possibly known, or that it is not significant, especially given how potentially serious the consequences are for patients.

It a clear warning sign about serious underlying physiopathology, consistent with what patients have been reporting for decades, and there are no excuses for it to not be paid serious heed.