Physical functioning in patients with ankylosing spondylitis: comparing approaches of experienced ability with self-reported and objectively measured physical activity.

Background: Physical functioning can be assessed by different approaches that are characterized by increasing levels of individual appraisal. There is insufficient insight into which approach is the most informative in patients with ankylosing spondylitis (AS) compared with control subjects.

Objective: The objective of this study was to compare patients with AS and control subjects regarding 3 approaches of functioning: experienced ability to perform activities (Bath Ankylosing Spondylitis Functional Index [BASFI]), self-reported amount of physical activity (PA) (Baecke questionnaire), and the objectively measured amount of PA (triaxial accelerometer).