AIM: Adaptation of the Short QUestionnaire to Assess Health-enhancing physical activity (SQUASH) in order to improve measurement properties in axSpA patients.
METHODS: The original SQUASH was adapted using a qualitative stepwise approach with in-depth interviews including healthcare professionals and patients. Content validity was explored by comparing modified-SQUASH (mSQUASH) and original SQUASH. Next, mSQUASH was validated according to the OMERACT filter. International Physical Activity Questionnaire (IPAQ) was used as comparator and tri-axial accelerometer as gold standard for criterion validity and classification accuracy of intensity. Construct validity was assessed using Spearman correlations with clinical outcome assessments. For test-retest reliability, intra-class correlation coefficients (ICCs) were calculated. Responsiveness was assessed using standardized response mean (SRM), stratified by Anchor method.
RESULTS: The mSQUASH measured a systematically higher activity count and had less missing values (8% vs. 16%) then SQUASH. mSQUASH correlated better with accelerometer compared to IPAQ (ρ = 0.60 vs. ρ = 0.34). Accelerometer measured most activity in light intensity, whereas mSQUASH and IPAQ predominately measured moderate intensity. Correlations with ASDAS, BASDAI, BASFI and ASQoL were better for mSQUASH then IPAQ. Test-retest reliability was good in both questionnaires. In contrast to IPAQ, responsiveness was in correspondence with self-reported changes in physical activity for mSQUASH (SRM -0.84 for improvement and 0.88 for decrease). The average completion time of the mSQUASH was 7 minutes.
CONCLUSIONS: The development of the mSQUASH resulted in an easy applicable, valid, reliable and responsive questionnaire for the assessment of daily physical activity in axSpA patients, which can be used in research and daily clinical practice.