As of 2003, Simon Wessely was still advancing the theory that PEM "may be caused by eccentric muscle contractions leading to local microtrauma in muscles subjected to excess work (as occurs in anyone undertaking exertion after a period of inactivity)." Wessely S, Chronic fatigue syndrome. Psychiatry 2003: 2; 20-23 This is somewhat absurd, since the delayed onset muscle soreness that results from eccentric contractions will cause pain only when the affected muscle is being used, not when it is at rest. His theory also does not account for non-musclular PEM symptoms. I think there's a really good reason that orthopedic specialists and even physiotherapists are never included in the papers where those sorts of assumptions about PEM are made - it's just so blatantly wrong at such a basic level as to be completely ridiculous.