Physical Fitness in Patients With Ankylosing Spondylitis: Comparison With Population Controls

Abstract

Background Although flexibility traditionally has been the main focus for physical therapy in patients with ankylosing spondylitis (AS), there is now evidence for an increased risk of cardiovascular diseases (CVDs) in this group. Objective The purposes of this study were: (1) to compare physical fitness (cardiorespiratory fitness, muscular capacity, flexibility, and balance) in patients with AS and controls and (2) to explore associations between physical fitness and disease activity in the patient group. Design This was a cross-sectional study. Methods The physical fitness variables were cardiorespiratory fitness (treadmill test for estimation of peak oxygen uptake [V̇o2peak]), muscular capacity (push-ups test), balance (30-second single-leg stand and walking in a figure-of-eight pattern), and flexibility (Bath Ankylosing Spondylitis Metrology Index [BASMI]). The Ankylosing Spondylitis Disease Activity Score (ASDAS) was used to assess disease activity. Group differences and associations were tested with the chi-square test for categorical variables, the Mann-Whitney U test for ordinal variables, and analysis of covariance for continuous variables. Results One hundred forty-nine of 250 of the invited patients with AS and 133 of 329 of the invited controls were included in the study. The mean ASDAS score of the patient group was 2.3 (range=0.5–4.7), and the median disease duration was 23 years (range=7–55). The patient group had significantly lower V̇o2 peak values, with a mean difference of −2.7 mL·kg−1·min−1 (95% confidence interval=−4.3, −1.1), and higher BASMI scores, with a mean difference of 1.6 (95% confidence interval=1.5, 1.8), compared with the control group. No group differences were found in balance or muscular capacity. In the patient group, significant inverse associations were found between ASDAS scores and V̇o2peak and muscular capacity. Limitations The response rate was lower in the control group (40.4%) than in the patient group (59.6%). Conclusion The lower cardiorespiratory fitness and reduced flexibility in the AS group indicate that physical therapy programs should include cardiorespiratory fitness exercises as a basic component to reduce the risk of cardiovascular disease.