Decreased physical activity and cardiorespiratory fitness in adults with ankylosing spondylitis: a cross-sectional controlled study

The health benefits of physical activity (PA) in the general population are numerous; however, few studies have measured PA among adults with ankylosing spondylitis (AS). The aims of this study were to: (1) objectively measure the PA levels and cardiorespiratory fitness of adults with AS and compare these to population controls, and (2) examine the relationships between PA, cardiorespiratory function and condition-specific outcomes. This cross-sectional study included participants (>18 years) meeting the modified New York criteria for AS, and matched population controls. Exclusion criteria were the presence of comorbidities limiting PA, or recent changes in medication usage. Participants completed clinical questionnaires assessing disease activity, physical function and quality of life. Tri-axial accelerometers recorded habitual PA over 1 week. Cardiorespiratory fitness was assessed by submaximal treadmill test with breath-by-breath gas analysis and heart rate monitoring. Thirty-nine adults with AS and 39 controls were recruited. The AS group spent significantly less time performing vigorous-intensity PA than controls [mean difference (95 % CI) 1.8 min/day (1.2–2.7)] and performed significantly fewer bouts of health-enhancing PA [1.7 min/day (1.1–2.5)]. The AS group had significantly lower predicted VO_2MAX than controls [6.0 mL kg⁻¹ min⁻¹ (1.8–10.1)]. PA was associated with aerobic capacity. Sedentary time was associated with disease activity and physical function. Adults with AS participate in less health-enhancing PA than population controls. Fewer than half meet PA recommendations, despite exercise being a key component of AS management. Explorations of PA behaviour and strategies to increase PA participation are needed.