Avoidance behavior towards physical activity in chronic fatigue syndrome and fibromyalgia: the fear for post-exertional malaise
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- Nijs, J. & Lundberg, M. Clin Rheumatol (2014) 33: 151. doi:10.1007/s10067-013-2421-1
We have read the Letter to the Editor written by Dr. Enlander  who commented on our review article addressing fear of movement and avoidance behavior towards physical activity in patients with chronic fatigue syndrome (CFS) and fibromyalgia (FM) . We would like to thank Dr. Enlander for his interest in our review paper and for his efforts in stimulating international debate in this area. However, we feel that Dr. Enlander's letter is offline with the scope of the review article and, therefore, would like to take the opportunity to restore the focus.
We do not question the importance of post-exertional malaise for CFS and FM as highlighted by Dr. Enlander. We agree that the severe exacerbation of symptoms following exercise, as seen in CFS patients, is one of the core features of the illness [3, 4]. Moreover, we have contributed to a better understanding of post-exertional malaise in CFS patients. In an exercise immunology study, we showed that the change in complement C4a level was strongly related to the increase in pain and fatigue 24 h following the self-paced, physiologically limited exercise . The same study revealed that postexercise elastase activity level and the change in elastase activity level were inversely related to the fatigue increase 1 h following the self-paced, physiologically limited exercise . These findings suggest that subtle alterations in blood elastase activity level and complement C4a split product levels account in part of post-exertional malaise in people with CFS. An increasing number of studies have examined the response of the immune system to exercise in CFS patients (e.g., [4, 5, 6, 7, 8, 9, 10]), yet the abnormal immune responses to exercise in CFS patients have not been conclusively defined and it remains unclear whether exercise-induced immune abnormalities can be regarded as biomarker for CFS. Hence, we applaud the efforts by Dr. Enlander and his team for more study in this area. At the same time, we would like to alert him to the role of the brain's capacity to orchestrate top-down endogenous analgesia during exercise, which is another physiological mechanism that is malfunctioning not only in CFS but also in FM patients [11, 12, 13]. The lack of endogenous analgesia in response to exercise accounts in part for post-exertional malaise in CFS .
However, the biology of post-exertional malaise in CFS and FM was not the focus of our review. Besides biomedical factors, undoubtedly, psychological factors will contribute to post-exertional malaise in CFS and FM. Moreover, post-exertional malaise is most likely the result of the interplay between psychological and biomedical factors. Therefore, our review focused on one important psychological factor known to interfere with the (perceived) ability to perform movements and physical activities and the (perceived) capacity of one's body to cope with such efforts. More precisely, the review addressed fear of worsening symptoms due to physical activity/body movement and avoidance of such physical activities/body movements by patients with CFS and FM. It was concluded that fear of movement and avoidance behavior towards physical activity are highly prevalent in both CFS and FM and are related to various clinical symptom severities, self-reported quality of life, and disabilities . Furthermore, the review showed that identifying CFS and FM patients displaying fear of movement and avoidance behavior towards physical activity is crucial for treatment (success) and that individually tailored cognitive behavioral therapy plus exercise training is the most promising strategy for treating fear of movement and avoidance behavior towards physical activity in patients with CFS and FM . Such conclusions do not, in any way, outrule the possible role of biomedical factors in determining exercise performance and post-exertional malaise in ME/CFS. Adopting a broad biopsychosocial view is required for understanding, studying, and treating complex disorders like FM and CFS.