so there’s research out of the Workwell Foundation on two consecutive cardiopulmonary exercise tests in ME/CFS patients. the finding that got me: when healthy controls repeat the test 24 hours later, their anaerobic threshold holds or improves slightly. when ME/CFS patients do it, the threshold drops measurably on day two. i’ve been a PT for twenty years and i knew anaerobic threshold from sports rehab.
what i didn’t understand until i read this: in ME/CFS the threshold isn’t just subjectively lower. it’s objectively impaired and then impaired further by prior exertion. so the window you had on monday is smaller on tuesday, not because you feel tired, but because something in the energy system itself is compromised. this reframed pacing for me completely.
“rest before you’re tired” always sounded like a discipline problem, like willpower. turns out it’s more like: if you cross threshold on monday, tuesday’s ceiling is lower and you may not even know it until the crash arrives wednesday. you can’t pace to a fixed target because the target moves based on what you did 24-48 hours ago. eighteen months in, i still can’t always feel where the line is before i cross it.
the brain fog is sometimes the only warning and it arrives too late. has anyone tried using heart rate monitoring as a proxy for anaerobic threshold during daily activity? been experimenting with an HR ceiling but the number keeps shifting on me.