Open Access Open Badges Research article

Moving instead of asking? Performance-based tests and BASFI-questionnaire measure different aspects of physical function in ankylosing spondylitis

Salima FE van Weely1*, J Christiaan van Denderen1, Martijn PM Steultjens2, Marike van der Leeden13, Michael T Nurmohamed14, Joost Dekker135, Ben AC Dijkmans14 and Irene E van der Horst-Bruinsma4

Author affiliations

1 Reade, Centre for Rehabilitation and Rheumatology, Dr. Jan van Breemenstraat 2, PO Box 58271, 1040 HG Amsterdam, the Netherlands

2 Glasgow Caledonian University, Institute for Applied Health Research, Glasgow City G4 0, Scotland, UK

3 VU University Medical Centre, Department of Rehabilitation Medicine, EMGO Institute, PO Box 7057, 1007 MB Amsterdam, The Netherlands

4 VU University Medical Centre, Department of Rheumatology, PO Box 7057, 1007 MB Amsterdam, The Netherlands

5 VU University Medical Centre, Department of Psychiatry, PO Box 7057, 1007 MB Amsterdam, The Netherlands

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Citation and License

Arthritis Research & Therapy 2012, 14:R52  doi:10.1186/ar3765

Published: 8 March 2012



Ankylosing Spondylitis (AS) is characterised by limitations in physical function. The Bath Ankylosing Spondylitis Functional Index (BASFI) is considered to be the gold-standard to assess physical function in AS patients. However, the BASFI questionnaire is a self-reported outcome measure and susceptible to subjective interpretation (under- or over-estimation). More objective outcome measures, like performance-based tests, could provide an objective outcome measurement for the evaluation of limitations in physical function. Therefore, the primary aim of this study was to determine the association between performance-based measures and the BASFI questionnaire.


In this cross-sectional study 126 AS patients completed the BASFI questionnaire and eight performance-based tests based on BASFI-items. Each test received three scores: one for performance (time or points) and a score for exertion and pain experienced during performance (using modified Borg-scale and VAS 0-100 mm, respectively). Linear regression analyses were used to assess the associations between the BASFI questionnaire and performance-based tests.


The univariable association between performance and BASFI-score was moderate with a R-square of 0.31 and Beta of 0.56 (p's < 0.05). In a multivariable analysis, the association between performance, exertion and pain on the one hand and BASFI-score on the other was assessed; R-square increased to 0.54: the Beta's for exertion and pain during performance were 0.38 and 0.26, respectively; the Beta for performance decreased to 0.19 (p's < 0.05).


This study demonstrates that alongside actual performance, patients seem to incorporate exertion and pain in their assessment of perceived physical function on the BASFI questionnaire. Performance-based tests could provide an objective outcome measurement for the evaluation of physical function and give relevant new information in addition to the BASFI questionnaire.