Associations of physical activity levels with fatigue in people with inflammatory rheumatic diseases in the LIFT trial.

Objectives: The overall aim of the current study was to quantify physical activity levels in inflammatory rheumatic diseases (IRDs) and to explore their role in fatigue. Methods: We conducted a secondary analysis of data from the Lessening the Impact of Fatigue in IRDs (LIFT) trial of the personalized exercise program (PEP) intervention for fatigue. Participants with IRDs were recruited from 2017 to 2019 and the current analysis used fatigue, measured by the Chalder Fatigue Scale (CFS) and the Fatigue Severity Scale (FSS), and accelerometer measured physical activity data collected at baseline and at the 6-month follow-up. Physical activity levels were quantified and associations with fatigue and effects of PEP investigated. Results: Of the 337 included participants, 195 (68.4%) did not meet the current recommendations for moderate-vigorous physical activity (MVPA). In baseline cross-sectional analysis, many dimensions of physical activity were associated with fatigue. After mutual adjustment, overall physical activity (vector magnitude) was associated with CFS [-0.88 (95% CI -0.12, -1.64)] and distribution of time spent at different activity intensities was associated with FSS [-1.16 (95% CI -2.01, -0.31)]. Relative to usual care, PEP resulted in an increase in upright time, with trends for increases in step count and overall physical activity. People who increased overall physical activity (vector magnitude) more had greater improvements in CFS and FSS, while those who increased step count and MVPA more had greater improvements in FSS. Conclusion: Increasing physical activity is important for fatigue management in people with IRDs and further work is needed to optimize PEPs to target the symptoms and impact of fatigue. Trial registration: ClinicalTrials.gov (http://clinicaltrials.gov), NCT03248518.