Impact of disease burden on VO₂max, physical performance and frailty in ankylosing spondylitis: a comparative...

To examine the association between spinal mobility, disease activity, frailty and cardiorespiratory fitness (maximal oxygen uptake (VO₂max)) in patients with ankylosing spondylitis (AS).

A cross-sectional comparative study was conducted at the University of Lahore and seven government hospitals (March-August 2025) including 74 patients with AS (40-55 years, modified New York criteria) and 77 age-matched and sex-matched healthy controls. Assessments included disease activity (Bath Ankylosing Spondylitis Disease Activity Index), functional limitation (Bath Ankylosing Spondylitis Functional Index), spinal mobility (Bath Ankylosing Spondylitis Metrology Index (BASMI)), chest expansion, frailty (Fatigue, Resistance, Ambulation, Illnesses, Loss of weight scale), pulmonary function and cardiorespiratory fitness (VO₂max) via symptom-limited cardiopulmonary exercise testing. Functional performance was measured with the 6 min walk test (6MWT), and physical activity with the International Physical Activity Questionnaire (IPAQ). Data were analysed using t-tests, χ² tests, correlations and regression models to examine associations between clinical measures and cardiorespiratory fitness.

Among 151 participants (74 AS, 77 controls), AS patients showed significantly reduced pulmonary function (forced expiratory volume in one second 83.5% vs 91.2%, forced vital capacity 85.1% vs 93.0%), lower VO₂max (27.8 vs 33.4 mL/kg/min), impaired spinal mobility (BASMI 5.1 vs 1.2) and decreased chest expansion (2.8 vs 5.6 cm; all p<0.01). They also had shorter 6MWT distance, higher frailty and lower physical activity. VO₂max was inversely correlated with disease activity, spinal stiffness, frailty and structural damage and positively correlated with chest expansion, 6MWT and activity levels. AS status, higher disease activity, greater spinal stiffness and reduced chest expansion independently predicted low physical activity.

AS is associated with impaired pulmonary function, reduced spinal mobility and lower cardiorespiratory fitness, with disease activity, stiffness and restricted chest expansion potentially influencing physical activity and overall functional capacity.