Research from Newcastle University finds a subgroup of CFS patients are unable to benefit from exercise therapy.

Loss of capacity to recover from acidosis on repeat exercise in Chronic Fatigue Syndrome: A case control study.

Conclusion: When exercising to comparable levels to normal controls CFS patients exhibit profound abnormality in bioenergetic function and response to it. Although exercise intervention is the logical treatment for patients showing acidosis any trial must exclude subjects who do not initiate exercise as they will not benefit. This potentially explains previous mixed results in CFS exercise trials.