"Relapses are precipitated by undue physical or mental stress"
The postviral syndrome: a review. MI Archer JRCGP 1987:37:212-216.
In more acutely affected individuals the advice to exercise back to fitness is a recipe for disaster.
The postviral fatigue syndrome WRC Weir Current Medical Literature (Royal Society of Medicine) 1992:6:1
Any kind of muscle exercise can cause the patient to be almost incapacitated for some days afterward. In severe cases, the patient is usually confined to bed. What is certain is that when one reviews (the) clincal features and laboratory results, it becomes plain that this is an organic illness in which muscle metabolism is severely affected.
Postviral fatigue syndrome PO Behan WMH Behan, Crit Rev Neurobiol 1988:4:2:157-178
"The abnormalities we found provide clear evidence for central nervous system and neuromuscular involvement". Carolyn L Warner: Neurology, March 1989:39:3: Suppl 1:420; Presentation at the American Acadamy of Neurology Conference, Chicago, April 1989.
The purpose of this study was to determine if patients with CFS have less vagal power during walking and during rest periods following walking...Patients had significantly less vagal power than the control subjects, despite there being no significant group-wise differences in mean heart rate, tidal volume, minute volume, respiratory rate, oxygen consumption or total spectrum power. Notably,
patients with CFS had a significant decline in resting vagal power after periods of walking. These results suggest a subtle abnormality in vagal activity to the heart in patients with CFS. Decreased vagal power during treadmill walking in patients with chronic fatigue syndrome Cordero DL Natelson BH et al. Clin Auton Res: 1996:6

6):329-333
"Complaints of muscle weakness and pain are common, and abnormal muscle metabolism has been reported to occur in CFS. CFS patients had recovery for rates for oxygen saturation that were 60% lower than those for recovery of oxygen saturation of normal subjects.
The present study has demonstrated direct impairments in oxygen delivery in CFS patients compared with normal controls. These impairments were more clearly seen after exercise. The impaired oxygen delivery seen in the CFS subjects in the present study could result in reduced exercise capacity"
Impaired oxygen delivery to muscle in chronic fatigue syndrome. Kevin K McCully Benjamin H Natelson Clinical Science 1999:97:603-608.
The standard for measuring exercise capacity has always been the maximal oxygen uptake (VO2 max) during high intensity whole body exercise..Our patients with CFS had an average VO2 max just below 20 mL/kg per minute, representing significant impairment relative to the controls...Comparing the exercise capacity in our patients with data from other studies shows a functionality similar to that of individuals with chronic heart failure, patients with chronic obstructive pulmonary disease, and those with skeletal muscle disorder
Exercise Capacity in Chronic Fatigue Syndrome, Pascale de Becker Neil McGregor Kenny De Meirleir et al Arch Intern Med 2000:160:3270-3277
"Wessely et al (JRCGP 1989:39:26-29) hypothesized that physical deconditioning might play an important role in CFS..In the present study, CFS patients did not have a worse physical fitness compared with controls...
physical deconditioning does not seem a perpetuating factor in CFS.
Is physical deconditioning a perpetuating factor in chronic fatigue syndrome? A controlled study on maximal exercise performance and relations with fatigue, impairment and physical activity, Bazelmans E et al, Psychological Medicine 2001:31:107-114
The present review examines the cytokine response to acute exercise stress...
The main source of the exercise-induced IL-6 production appears to be exercising muscle...Cytokine concentrations are increased in CFS..Exercise-induced modulations in cytokine secretion may contribute to allergies Cytokine response to physical activity, with particular reference to IL-6: sources, actions and clinical implications Shepherd RJ Crit Rev Immunol 2002:22:3:165-182
"
These results implicate abnormal immune activity in the pathology of exercise intolerance in CFS and are consistent with a channelopathy involving oxidative atress and nitric-oxide-related toxicity...In CFS patients, the accentuated and prolonged postexercise oxidative stress may be responsible for muscle membrane alterations with the consequences of the impaired membrane excitability described here...Thus, as in inherited muscular dystrophy, an increased level of free radical damage may be a contributor to the underlying defects and symptom presentation.
Exercise capacity and immune function in male and female patients with chronic fatigue syndrome Snell CR et al In Vivo 2005:19:2:387-390
It is evident that ion transport and ion channel activity segregate cases from controls and that exercise seems to intensify these differences...Several other conditions have been reported that are known to be caused by abnormal ion channels. These include myasthenic syndromes, multiple sclerosis, and polyneuropathies"
Exercise responsive genes measured in peripheral blood of women with Chronic Fatigue Syndrome and matched controls Toni Whistler James F Jones Elizabeth R Unger Suzanne Vernon BMC Physiology 2005:5:5