Exploratory Analysis of the Relationships between Aerobic Capacity and Self-Reported Fatigue in Patients with Rheumatoid Arthritis, Polymyositis, and Chronic Fatigue Syndrome

Objective To determine if self-reported levels of physical activity and fatigue are related to peak oxygen uptake (VO2peak ) and whether these relationships differ among the patient groups (rheumatoid arthritis [RA], polymyositis [PM], and chronic fatigue syndrome [CFS]). Design Correlational investigation. Setting Two ambulatory research clinics at the National Institutes of Health, Clinical Center, Bethesda, MD. Participants There were 9 patients with PM, 10 with RA, and 10 with CFS. All patients met case criteria for their respective diagnoses. Methods/Main Outcome Measurements VO2peak during bicycle ergometry and self-reported fatigability, fatigue, and physical activity. VO2peak was used as the criterion measurement of physiological fatigue with which the self-reported variables were compared. Results The Pearson r revealed that self-reported physical activity correlated with VO2peak ( r = 61, P = .01). However, fatigability and fatigue did not correlate with VO2peak . Linear regression analysis was performed to assess the effects of diagnosis group, self-reported activity level or fatigue, and their interaction. A trend in the data showed a distinctive relationship between fatigue/fatigability within the 3 groups. In addition, when controlling for group status, self-reported activity predicted aerobic capacity as measured by VO2peak. Conclusions This study confirms that patients with chronic, but stable RA, PM, or CFS are fatigued and have significantly decreased aerobic capacity. Self-reports of physical activity predicted VO2peak , and may be used as an indicator of activity-based aerobic capacity. Self-reports of fatigue, however, did not correlate with VO2peak and hence are assessing something other than an index of aerobic capacity, and provide additional information about patients' perceptions, which will require further investigation.