Wiborg (2010)
https://pubmed.ncbi.nlm.nih.gov/20047707/
1. Summary: CBT does not increase physical activity in CFS patients, as measured by actigraphy. In particular, the self-report fatigue and actigraphy results did not correlate, so there is simply no possibility of CBT having a causal effect on activity levels.
2. It came out before PACE (Feb 2011).
3. @Tom Kindlon asked the PACE authors why they dropped actigraphy for the outcome (after collecting a full set of baseline data). Their answer (on the public record, in a formal journal), was that the patient organisation involved in the trial (Action for ME) had agreed/advised (?) that the actimeters themselves were "too much of a burden on patients".
Actimeters are deliberately designed to be as unobtrusive as possible, and weigh less than 50gm (1.75 oz). I have a light short-sleeved summer cotton shirt that weighs 151gm. Wearing that is no burden.
4. Subsequently, information that came out of an FOI by @JohnTheJack revealed that the reason PACE gave to the Trial Steering Committee (?) for dropping the actigraphy was that results of the Wiborg study were negative, they did not support an effect from CBT. PACE argued that they should only be required to use measures that gave positive results.
Let that sink in. They are claiming to be exempt from falsifiability. To be allowed to use a methodology that can never prove they are wrong.
And so here we are...
I've worn an actimeter before my treatment with CBT/GET and it wasn't a bother at all. The thing got hooked up and the only time I had to mind it was whilst showering. This was in 2003, I'd imagine the devices have gotten better and even less intrusive over time, but I'm not sure about that.