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Hypothesis: The pathophysiological basis of decreased motor performance in CFS may, theoretically, involve three components:

1. A peripheral energetic deficit (impaired oxidative metabolism and/or physical deconditioning);

2. A central perceptual disturbance (higher effort sense or increased 'interoception'); and

3. A fundamental failure of the neurobiological stress system, leading to an abnormal 'sickness response'.

It is proposed that the first two components may lead to low effort capacity, while the third component may lead to reduced effort tolerance.

Although there is evidence for low effort capacity influencing symptoms and functional limitations in CFS, it is assumed that reduced effort tolerance might be the primary disturbance in CFS.

Diagnostic Implications: Distinguishing low effort capacity and reduced effort tolerance may contribute to a refinement of current diagnostic criteria of CFS and the identification of subgroups.

Therapeutic Implications: The above-mentioned distinction may make it possible to formulate a rationale for an effective implementation and adequate outcome evaluation of rehabilitation strategies in CFS.

Research implications: This new heuristic [problem-solving] framework may inform future research aimed at disentangling the complex determination of impaired motor performance in CFS, as well as studies aimed at customizing treatment to different subtypes of patients.

Source: Clinical Rehabilitation. 2007 Dec;21(12):1121-42. PMID: 18042608, by Van Houdenhove B, Verheyen L, Pardaens K, Luyten P, Van Wambeke P. Faculty of Medicine, KU Leuven, Leuven, Belgium. [E-mail: boudewijn.vanhoudenhove@uz.kuleuven.ac.be]