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Background This study aimed to explore the association of the sarcopenia questionnaire Strength, Assistance with walking, Rise from a chair, Climb stairs, Falls (SARC-F) with muscle strength, physical performance, daily activity, patient-reported outcomes (PROs) and body composition in patients with axial spondyloarthritis (axSpA) and psoriatic arthritis (PsA).Methods In this cross-sectional study, patient and disease characteristics including physical function, performance measures and body composition assessed by dual-energy X-ray absorptiometry (DXA) were analysed. Variables were compared between patients with a SARC-F score ≥4 and <4, higher versus lower sarcopenia risk. Linear regression examined associations, adjusted for age and sex.Results Overall, 54 of 213 patients with SpA (65.7% axSpA, 34.3% PsA) had a SARC-F score ≥4 (24.4%). DXA identified sarcopenia and sarcopenic obesity in 4 patients each (7.7%). Patients with SARC-F scores ≥4 were older, predominantly female or obese, had longer disease duration, higher disease activity, lower physical performance, decreased muscle strength and daily activity and more unfavourable body composition. Total SARC-F score was consistently associated with muscle strength, physical performance, PROs and DXA components. Higher body mass index and patient global assessment were independently associated with higher SARC-F scores. The SARC-F ≥4 threshold showed moderate specificity (76%) but low sensitivity (50%) for DXA-defined sarcopenia, with a high negative predictive value (97%).Conclusions SARC-F was significantly associated with disease activity, muscle strength and physical performance, but showed limited ability to identify DXA-defined sarcopenia. Further research is needed to clarify its clinical utility for risk stratification in rheumatic diseases.