The value of performance-based tests in the assessment of patients with fibromyalgia: a construct validity and comprehensiveness analysis of a standardized test battery.

Background: Comprehensive assessment of functioning in fibromyalgia (FM) requires the integration of objective and subjective outcome measures. Although performance-based tests (PBTs) are increasingly recommended for evaluating physical function, evidence supporting their construct validity within a standardized multidimensional assessment framework remains limited. Furthermore, the complementary contribution of accelerometer-derived physical activity measures has not been fully established. Objective: To evaluate the construct validity and comprehensiveness of a standardized assessment battery integrating PBTs, patient-reported outcome measures (PROMs), and accelerometer-derived physical activity measures in women with FM within an International Classification of Functioning, Disability and Health (ICF)-based framework. Methods: A cross-sectional study included 87 women with FM recruited from four tertiary hospitals. Participants completed four PBTs (6-minute walk test, handgrip strength test, 8 foot up and go test, and Berg Balance Scale), accelerometer-based physical activity assessment, and validated Spanish PROMs assessing physical functioning, emotional distress, and pain impact and symptom burden. Construct validity was evaluated by testing predefined hypotheses for convergent and discriminant validity using Spearman correlations. Exploratory factor analysis (EFA) was conducted to examine the latent multidimensional structure of the proposed assessment framework. Results: The EFA identified four latent constructs corresponding to physical functioning, activity behavior, emotional distress, and pain impact and symptom burden, explaining 67.1% of the total variance. The physical functioning construct accounted for the largest proportion of explained variance (22.6%), followed by activity behavior (18.6%), emotional distress (13.3%), and pain impact and symptom burden (12.7%). Correlation analyses supported the predefined hypotheses, demonstrating moderate to strong within domain associations and generally weak to moderate between domain correlations, confirming both convergent and discriminant validity. ICF mapping showed that the proposed battery provided broad coverage of key body functions and activity domains, while accelerometer-derived variables emerged as an independent construct, supporting their complementary value beyond PBTs and PROMs. Conclusion: The proposed standardized assessment battery demonstrates strong construct validity and provides a comprehensive ICF-based evaluation of functioning in women with FM. The combination of PBTs, accelerometry, and PROMs offers a multidimensional characterization of functioning that may improve functional assessment, individualized rehabilitation planning, and treatment monitoring. Clinical Trial Registration: https://clinicaltrials.gov/study/NCT06819930, identifier NCT06819930.