Studies looking at PEM - have they measured PEM or just the response to the challenge used?

Todd Davenport, of the Workwell Foundation, was asked if the 2xCPET measured PEM or the associated energy loss. The start of his answer is

"Thanks for this interesting question and set of observations. I appreciate you sharing them, as I also appreciate the chance to share. In the first part of the thread, you asked whether I think CPET measures PEM or the energy deficit associated with it. I think it is the latter."

Further down his thread on Twitter he also notes,

"Not only do we see differences in metabolism and work rate between CPETs, but people with ME/CFS also have signs and symptoms of PEM, so we know those two things are going together. As you point out, PEM itself is *not a symptom.* A common mistake clinicians and researchers make."

"That last part is important and a lot of smart people get it wrong all the time: PEM itself is not a symptom. It is a whole host of symptoms and signs that occurs following some kind of exertion (more on that soon, I promise), reflecting a complex multi-system pathology."

More can be found via the tweet linked above.

 

I would say Sonja Kohl has got this wrong. PEM is not a mechanism. It is a temporal pattern of symptoms. It is symptoms. And whether or not it reflects 'multi-system pathology' seems to me to be purely speculative and rather unhelpful.

At least Davenport seems to be right in saying that CPET doesn't actually measure PEM.

He does seem to think he can assume it does indirectly though.