Obesity is more strongly associated with physical performance and body composition than sarcopenia in patients with spondyloarthritis.

OBJECTIVES: Integrated data on body composition, objective physical performance and daily physical activity are limited in spondyloarthritis (SpA). The objective of this study is to describe DXA-derived body composition phenotypes and examine their cross-sectional associations with objective physical performance and daily physical activity in axial SpA (axSpA) and psoriatic arthritis (PsA). METHODS: In this single-center cross-sectional study, 213 patients with axSpA or PsA underwent performance testing and completed the mSQUASH questionnaire. Obesity was defined using DXA-derived body fat percentage (≥30% in men, ≥40% in women). Physical activity was categorized into tertiles. ANCOVA models adjusted for age, BMI and diagnosis assessed independent effects of physical activity on performance and body composition. RESULTS: Physical performance was largely preserved. DXA-defined obesity was common whereas sarcopenia was rare. Higher levels of daily activity were consistently associated with better physical performance and favorable body composition. Patients in the highest mSQUASH activity tertile demonstrated significantly higher grip strength (45.3 (13.0) kg), faster gait speed (1.60 (0.27) m/s), and higher SPPB scores (11.5 (1.0), alongside lower FMI and higher ALM/BMI. In sex-stratified analyses, TNFi-treated men had lower body fat and obesity prevalence than men on conventional therapy; no differences were observed in women. In adjusted models, daily physical activity remained independently associated with ALM/BMI, grip strength and ASPI, whereas diagnosis showed no independent association. CONCLUSION: In SpA, DXA-defined obesity was common and associated with worse objective performance, whereas sarcopenia was rare. Higher levels of daily physical activity were independently associated with better physical performance and more favourable muscle-related body composition indices.