title: Physical functioning in patients with ankylosing spondylitis: comparing approaches of experienced ability with self-reported and objectively measured physical activity.
abstract: 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).
  
  
  METHODS
  This case-control study included 24 AS patients and 24 control subjects (matched for age, gender, and body mass index). Subjects completed the BASFI and Baecke questionnaire and wore a triaxial accelerometer. Subjects also completed other self-reported measures on disease activity (Bath AS Disease Activity Index), fatigue (Multidimensional Fatigue Inventory), and overall health (EuroQol visual analog scale).
  
  
  RESULTS
  Both groups included 14 men (58%), and the mean age was 48 years. Patients scored significantly worse on the BASFI (3.9 vs 0.2) than their healthy peers, whereas PA assessed by Baecke and the accelerometer did not differ between groups. Correlations between approaches of physical functioning were low to moderate. Bath Ankylosing Spondylitis Functional Index was associated with disease activity (r = 0.49) and physical fatigue (0.73) and Baecke with physical and activity related fatigue (r = 0.54 and r = 0.54), but total PA assessed by accelerometer was not associated with any of these experience-based health outcomes.
  
  
  CONCLUSIONS
  Different approaches of the concept physical functioning in patients with AS provide different information. Compared with matched control subjects, patients with AS report more difficulties but report and objectively perform the same amount of PA.
authors.affiliation: From the *Division of Rheumatology, Department of Internal Medicine, Maastricht University Medical Centre/CAPHRI School of Public Health and Primary Care, †Faculty of Medicine, and ‡Department of Human Biology, NUTRIM School for Nutrition, Toxicology & Metabolism, Maastricht University Medical Centre +, Maastricht, the Netherlands.
authors.forename: Simon
authors.initials: S
authors.lastname: van Genderen
authors.forename: Carlie
authors.initials: C
authors.lastname: van den Borne
authors.forename: Piet
authors.initials: P
authors.lastname: Geusens
authors.forename: Sjef
authors.initials: S
authors.lastname: van der Linden
authors.forename: Annelies
authors.initials: A
authors.lastname: Boonen
authors.forename: Guy
authors.initials: G
authors.lastname: Plasqui
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D004185:Disability Evaluation; D005221:Fatigue / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D010808:Physical Examination; D057566:Self Report; D012720:Severity of Illness Index; D013167:Spondylitis, Ankylosing / Q000175:diagnosis / Q000503:physiopathology*; D011795:Surveys and Questionnaires; D064232:Visual Analog Scale; D055815:Young Adult