One of the central tenants of the CBT/GE treatment model for ME/CFS put forward by its proponents is that the patients avoid exercise because of an irrational or unfounded belief that exercise will make their symptoms worse. It is believed that cognitive and behavioural factors are involved in the persistence of fatigue and therefore treatment should be directed at these factors.  “Fear avoidance beliefs are characterised by fears that activity or exercise will make symptoms worse.” 
Given how this treatment approach is being promoted it might therefore be assumed that the biomedical research into CFS would support this theory that the patient’s fear of exercise making their symptoms worse is unfounded and that no link would be found between measurable biological effects and the patient’s symptoms. This however is not the case and there is clear evidence of biological effects of exercise in CFS patients which supports the patient’s experience of a worsening of symptoms and which does not support the view that the patients experience is unfounded.
Dr Weir in his response has already mentioned the research of Dr Mark VanNess and his colleagues who have shown that post exertional malaise is real and demonstratable in Chronic Fatigue Syndrome and not just imagined by patients. , Their finding of “diminished cardiopulmonary capacity during post-exertional malaise in Chronic Fatigue Syndrome” is striking in that it directly contradicts the belief that CFS patient’s fear of exercise making their symptoms worse is unfounded. Findings repeated by Keller.  Here is real biological data that backs up the patient experience.
This research is entirely consistent with other biomedical research showing evidence of impairment related to exercise in Chronic Fatigue Syndrome patients. To quote a few examples “Impaired oxygen delivery to muscle in Chronic Fatigue Syndrome” found by McCully KK, et al. “, “Loss of capacity to recover from acidosis on repeat exercise in Chronic Fatigue Syndrome” found by Jones DE, et al  and “Demonstration of delayed recovery from fatiguing exercise in Chronic Fatigue Syndrome” shown by Paul L, et al.
Further evidence that the patients experience in Chronic Fatigue Syndrome is valid with regards to exercise is demonstrated in the work of Alan Light and his colleagues. Their 2009 paper titled “Moderate exercise increases expression for sensory, adrenergic and immune genes in Chronic Fatigue Syndrome patients, but not in normal subjects” , showed that there is again a measurably abnormal response to exercise/activity in this group of patients, it is not just an abnormal belief on the part of the patient. They have also found that “severity of symptom flare after moderate exercise is linked to cytokine activity in Chronic Fatigue Syndrome” .
In a subsequent paper titled “Differences in metabolite-detecting, adrenergic, and immune gene expression after moderate exercise in patients with Chronic Fatigue Syndrome, patients with Multiple Sclerosis, and healthy controls”, they concluded “Thus, the pathology of CFS may include a susceptibility to disproportionate fatigue in response to exercise stress that is uniquely expressed in this patient group. The pattern of gene expression may have potential for use as a biomarker for diagnosis and treatment responses.” 
Could it be that in the light of this biomedical evidence that the abnormal beliefs are actually held by those pushing the CBT/Graded Exercise treatments in line with their psychological model of the illness? Certainly all of this research calls into question the very validity of this belief held by the CBT/GE treatment model proponents that the CFS patient’s fear of exercise making their symptoms worse is unfounded.
And finally they say a picture says a thousand words, the image below shows the clear difference in sensory, immune and adrenergic markers in response to exercise in Chronic Fatigue Syndrome patients and controls that Alan Light and his colleagues found in their research published in 2009. 
In case it does not appear it may be found as slide 28 at the link below
1. Vercoulen JH. The persistence of fatigue in chronic fatigue syndrome and multiple sclerosis: development of a model. (J Psychosom Res. 1998 Dec;45(6):507-17.)
2. Chalder T, Goldsmith KA, White PD, Sharpe M, Pickles AR. Rehabilitative therapies for chronic fatigue syndrome: a secondary mediation analysis of the PACE trial. Lancet Psychiatry 14 Jan 2015, doi:10.1016/S2215-0366(14)00069-8.
3. Snell CR, et al. Discriminative validity of metabolic and workload measurements for identifying people with Chronic Fatigue Syndrome. (Phys Ther. 2013 Nov;93(11):1484-92.) http://ptjournal.apta.org/content/93/11/1484.full.pdf
4. Van Ness JM, et al. Diminished cardiopulmonary capacity during post-exertional malaise in Chronic Fatigue Syndrome. (Journal of Chronic Fatigue Syndrome. 2008;14:77–85.) http://informahealthcare.com/doi/abs/10.1300/J092v14n02_07
5. Keller BA, et al. Inability of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome patients to reproduce VO2 peak indicates functional impairment. (J Transl Med. 2014; 12: 104.) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4004422/pdf/1479-5876-12-104...
6. McCully KK, et al. Impaired oxygen delivery to muscle in Chronic Fatigue Syndrome. (Clin Sci. 1999;97:603–608.) http://www.clinsci.org/cs/097/0603/0970603.pdf
7. Jones DE, et al. Loss of capacity to recover from acidosis on repeat exercise in Chronic Fatigue Syndrome: a case-control study. (Eur J Clin Investig. 2012;42:186–194.) http://www.ncbi.nlm.nih.gov/pubmed/21749371
8. Paul L, et al. Demonstration of delayed recovery from fatiguing exercise in Chronic Fatigue Syndrome.(Eur J Neurol. 1999 Jan;6(1):63-9.) http://www.ncbi.nlm.nih.gov/pubmed/10209352
9. Light AR, et al Moderate exercise increases expression for sensory, adrenergic and immune genes in chronic fatigue syndrome patients, but not in normal subjects (J Pain. 2009 October ; 10(10): 1099–1112) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2757484/pdf/nihms125894.pdf
10. White AT, et al. Severity of symptom flare after moderate exercise is linked to cytokine activity in Chronic Fatigue Syndrome (Psychophysiology 2010 Jul 1;47(4):615-24. Epub 2010 Mar 4.) http://www.ncbi.nlm.nih.gov/pubmed/20230500
11. White AT, et al. Differences in metabolite-detecting, adrenergic, and immune gene expression after moderate exercise in patients with Chronic Fatigue Syndrome, patients with Multiple Sclerosis, and healthy controls. (Psychosom Med. 2012 Jan;74(1):46-54) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256093/pdf/nihms343418.pdf
Competing interests: No competing interests