Physical activity and the association with fatigue and sleep in Danish patients with rheumatoid arthritis

The aim of this study was to examine physical activity behavior in patients with rheumatoid arthritis and to identify potential correlates of regular physical activity including fatigue, sleep, pain, physical function and disease activity. A total of 443 patients were recruited from a rheumatology outpatient clinic and included in this cross-sectional study. Physical activity was assessed by a four-class questionnaire, in addition to the Physical Activity Scale. Other instruments included the Multidimensional Fatigue Inventory (MFI), the Pittsburgh Sleep Quality Index and the Health Assessment Questionnaire. Disease activity was obtained from a nationwide clinical database. Of the included patients, 80 % were female and mean age was 60 (range 21–88 years). Hereof, 22 % (n = 96) were regularly physically active, and 78 % (n = 349) were mainly sedentary or having a low level of physical activity. An inverse univariate association was found between moderate to vigorous physical activity, and fatigue (MFI mental, MFI activity, MFI physical and MFI general), sleep, diabetes, depression, pain, patient global assessment, HAQ and disease activity. The multivariate prediction model demonstrated that fatigue-related reduced activity and physical fatigue were selected in >95 % of the bootstrap samples with median odds ratio 0.89 (2.5–97.5 % quantiles: 0.78–1.00) and 0.91 (2.5–97.5 % quantiles: 0.81–0.97), respectively, while disease activity was selected in 82 % of the bootstrap samples with median odds ratio 0.90. Moderate to vigorous physical activity in patients with rheumatoid arthritis is associated with the absence of several RA-related factors with the most important correlates being reduced activity due to fatigue, physical fatigue and disease activity.