MADISON, Wis.—New research on exercise response in patients with chronic fatigue syndrome (CFS), with or without fibromyalgia (FM), finds little difference in cardiorespiratory response to exercise in either group compared with fitness-matched healthy controls and casts doubt on the role of "metabolic disease" in CFS. Dane B. Cook, PhD, assistant professor of kinesiology at the University of Wisconsin in Madison, reports in Arthritis & Rheumatism1 that patients with CFS plus FM perceived exercise as requiring more effort and being more painful than did controls or those with CFS alone, although they were not actually working any harder. These findings suggest that CFS patients without FM have normal nociceptive processing during exercise and that muscle contraction does not cause the hyperalgesia state in CFS patients.
Study weeds out effect of fitness, comorbid FM, in CFS patients
Dr. Cook set out to clarify how exercise affects CFS by weeding out the effects of comorbid conditions and aerobic fitness. He reports that cardiorespiratory responses to an incremental bicycle test among patients with CFS alone and CFS plus FM were similar to those seen in healthy sedentary individuals, once the investigators controlled for aerobic fitness.
FM is the most common comorbid condition occurring among CFS patients, with 43% to 70% of CFS patients fulfilling American College of Rheumatology criteria for FM. Previous studies on exercise and CFS have been equivocal, possibly due to nonstandard testing procedures, use of physically active as opposed to sedentary controls, and a failure to control for aerobic fitness levels or comorbid illness, the study team points out.
"The results of the present investigation highlight the importance of considering aerobic fitness level and the presence of comorbid illness in studies of exercise and CFS and provide insight regarding the functional and aerobic capacity of individuals with single and dual diagnoses," Dr Cook writes.
Metabolic hypothesis debunked?
The researchers studied 29 patients with CFS only, 23 patients with CFS plus FM, and 32 healthy sedentary controls who completed an incremental bicycle test to exhaustion. They measured cardiorespiratory and perceptual response to exercise for the entire sample and for 18 subjects from each group who were matched for peak oxygen consumption.
No significant differences in cardiorespiratory parameters were seen between the CFS-only group and the controls in the overall sample. The CFS-plus-FM group had lower ventilation, lower end-tidal carbon dioxide, and higher ventilatory equivalent of carbon dioxide compared with controls. The CFS-plus-FM patients also showed slower increases in heart rate compared with patients with CFS only and with healthy controls. Additional findings included lower peak oxygen consumption, ventilation, and workload in the CFS-plus-FM group.
These results held throughout the maximal exercise test and when the data were examined at ventilary threshold, suggesting that differences occurred when the groups were exerting similar metabolic effects; this may debunk the hypothesis implicating metabolic disease in the pathogenesis of CFS.
Participants in both the CFS-only group and the CFS-plus-FM group said that they found exercise to be more effortful than control subjects, while patients with CFS plus FM had more muscle pain than patients with CFS only or controls. In the subgroups matched for aerobic fitness, there were no significant differences among the groups for any measured cardiorespiratory response, but perceptual differences in the CFS-plus-FM group did not change.
"Extra care should be taken when prescribing an exercise regimen for an individual with diagnoses for both CFS and FM, since painful skeletal muscle contractions could lead to peripheral and or central hyperalgesia with a resulting increase in widespread pain," the researchers conclude. "Pain perception could be used to regulate the mode and intensity of exercise and to individually tailor the exercise program to account for the differences in physical function and levels of disability due to pain."
Others doubt that study gets to heart of issue
"The real day-to-day issues with CFS and FM patients really have to do with the day after exertion or exercise, not the day that it is performed," William Marcus Spurlock, MD, of the Fibromyalgia and Fatigue Centers of Dallas in Texas, told CIAOMed. "They usually have a setback that lasts days to weeks post-exertion, and his study did not address this major problem at all."
In addition, "I do disagree that the metabolic issues of CFS and FM should be called into question," Dr. Spurlick said. "This study was much too limited and insufficient to come to any conclusions about the effects of aerobic exercise on this group of patients. It did not address metabolic issues at all. The only conclusion that could be made is that patients with the dual diagnosis are more ill and respond more poorly than the patients with CFS only. These illnesses are extremely complex and involve multiple parameters that must be dealt with on an individual basis."
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Reference
- 1. Cook DB, Nagelkirk PR, Poluri A, Mores J, Natelson BH. The influence of aerobic fitness and fibromyalgia on cardiorespiratory and perceptual responses to exercise in patients with chronic fatigue syndrome. Arthritis Rheum. 2006;54:3351–3362.
