Secondary consequences of juvenile idiopathic arthritis in children and adolescents with knee involvement: physical activity, adiposity, fitness, and functional performance

Objective: Secondary consequences of juvenile idiopathic arthritis (JIA) may impact long-term health outcomes. This study examined differences in physical activity, cardiorespiratory fitness, adiposity, and functional performance in children and adolescents with JIA compared to their typically developing (TD) peers. Methods: Participants with JIA (n = 32; 10–20 years old) and their TD peers (n = 35) volunteered for assessments of: daily moderate-to-vigorous physical activity (MVPA, body-worn accelerometer); peak oxygen consumption (VO_{2 Peak}, incremental bike test); fat mass index (FMI, dual-energy X-ray absorptiometry); and triple-single-leg-hop (TSLH) distance. Statistical analyses were performed in R using four linear mixed-effect models with Bonferroni adjustment (⍺ = 0.0125). Fixed effects were group, sex, and age. Participant clusters based on sex and age (within 1.5 years) were considered as random effects. Results: Participants with JIA displayed lower mean daily MVPA than their TD peers [p = 0.006; β (98.75% CI); −21.2 (−40.4 to −2.9) min]. VO_{2 Peak} [p = 0.019; −1.4 (−2.5 to −0.2) ml/kg/min] decreased with age. Females tended to have lower V_{O2 Peak} [p = 0.045; −6.4 (−13.0 to 0.4) ml/kg/min] and greater adiposity [p = 0.071; 1.4 (−0.1 to 3.0) kg/m²] than males. Conclusion: The findings support the need for strategies to promote MVPA participation in children and adolescents with JIA. Sex and age should be considered in research on the consequences of JIA.