Does 'deconditioning' have any physical basis?
Is the claim that this is purely due to physical inactivity as in someone who's been doing bed rest, and normal responses to exercise - delayed onset muscle soreness et al?
The effects which he's attributing to deconditioning are far too severe for the reduced level of activity experienced by most patients. To experience OI from deconditioning, healthy controls have to literally lay in bed all day for a month or more with minimal movement. Most ME patients can at least sit up much of the day, and mild patients can even work full time, but will often still have significant OI.
It also requires ignoring whether the reduced activity came before or after the OI. Most patients report that it's OI (and PEM) which force them to become less active, not that they became less active and suddenly developed OI. The egRegius Sir Wessely's hypothesis would also require that decreased activity results in greater incapacity - yet many patients report that when forced to be inactive due to OI flares, or engage in aggressive resting, their OI and PEM thresholds actually improve afterward.
Additionally, deconditioned healthy people very quickly regain their previous level of conditioning. We're talking about weeks, versus the months or years the psychobabblers claim "deconditioned" ME patients will need. And if it was merely deconditioning, GET would show increased activity - whereas actometers and other objective measurements show no such improvements.
DOMS (delayed-onset muscle soreness) is a different issue regarding PEM, but used by psychobabblers in a similar hand-waving dismissal. In that case, they are equating the entirety of PEM to a hysterical reaction to DOMS. To do that they are ignoring about a dozen symptoms and choosing to focus on pain. But even their focus on pain ignores that DOMS is localized to the over-worked muscles and only when being used again, while PEM pain is more of a fully body experience and doesn't require to use the muscle for it to hurt.
It's pretty rare for physical therapists to promote these ideas, especially in a research setting, simply because they don't make sense. Hence it's almost entirely psychologists inventing vague theories to explain objective physical signs detected in patients, such as OI and CPET results.