Outdoor Exercise for People with Rheumatic Disease–Study Protocol and Baseline Characteristics of the OUTdoor Physical ACtivity Cohort (OUTPAC)

The OUTPAC cohort study evaluates the setup and implementation of a nationwide Danish initiative focused on the impact of structured outdoor physical activity (PA) on individuals with rheumatic diseases. This prospective cohort study includes more than 1600 participants, predominantly women (92%), with an average age of 65 years (range: 28–93). The cohort primarily consists of individuals with osteoarthritis (72%), rheumatoid arthritis (18%) and nonspecific lower back pain (13%). Volunteer instructors conducted interventions in outdoor settings, targeting strength, balance, physical capacity, mental health, and interaction with nature. Data collection involved questionnaires and physical tests in four primary outcome domains: quality of life, pain, physical function and activity, and mental health. Despite moderate pain (VAS mean: 48.3), high medication use (71%), and serious fatigue (54%), participants indicated having a good quality of life (EQ-5D-5L mean: 0.81) and average mental health (WHO-5 mean: 62.9). Baseline scores from physical tests showed results comparable to the general population aged 60–69 years. The OUTPAC project offers clinical insight into the implications of outdoor PA interventions on individuals with rheumatic disease while shedding light on the development and implementation of a large-scale nationwide outdoor PA intervention. Future analyses will examine short- and long-term changes and potential determinants.