Decreased health-related physical fitness in adults with ankylosing spondylitis: a cross-sectional controlled study.

OBJECTIVES

(1) Assess the health-related physical fitness of adults with ankylosing spondylitis (AS) and compare these to the general population, and (2) examine the relationships between physical fitness and condition-specific outcomes.

DESIGN

Cross-sectional, controlled study.

SETTING

Exercise research laboratory.

PARTICIPANTS

Thirty-nine adults with AS (32 men, 7 women) and 39 age- and gender-matched controls.

INTERVENTION: Comprehensive physical fitness assessment, and completion of questionnaires assessing disease activity, physical function and quality-of-life.

MAIN OUTCOME MEASURES: Body composition was assessed by bio-impedance analysis. Flexibility was measured with the Bath AS Metrology Index (BASMI). Cardiorespiratory fitness was assessed by submaximal treadmill test with breath-by-breath gas analysis and heart rate monitoring. Muscular strength and endurance were measured by isokinetic dynamometry of concentric knee flexion/extension.

RESULTS

The AS group demonstrated significantly lower cardiorespiratory fitness [mean difference -1.3mLmin(-1)kg(-1) (95% CI -1.1 to -1.4)], flexibility [0.4 BASMI units (0.2 to 0.7)], muscular strength [-31.6 peak torque per body weight dominant knee extension (-56.1 to -7.1)], and increased body fat [0.4% (0.0 to 1.2)] compared to population controls (p<.05). There were significant associations between each fitness component and physical function (p<.05). Higher aerobic capacity was significantly associated with improved quality-of-life. Fitness was not significantly associated with disease activity.

CONCLUSION

Adults with AS have significantly reduced health-related physical fitness compared to population controls. Decreased body fat, and higher aerobic capacity, muscular fitness and flexibility are significantly associated with improved function. These findings have implications for clinicians assessing adults with AS, and for targeted-exercise prescription in this cohort.