Truth is we are no closer to having a biomarker for fatigue. There is no particular reason why the normal fatigue that people get from working hard has anything to do with the chronic fatigue that ME/CFS and other chronic diseases face. ME/CFS is unique in its payback where a sufferers pushes through the fatigue and ends up with symptoms worsening and new symptoms 12-72 hours later that can last a day to the rest of their lives. That isn't just fatigue and the UK doctors have been trying to make ME/CFS all about fatigue since the 1980s and it caused immense harm. It actually has about 280 symptoms, of which fatigue is just one and not even the most debilitating or important one.