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.


 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 (VO2 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].  VO2 Peak [p = 0.019; -1.4 (-2.5 to -0.2) ml/kg/min] decreased with age.  Females tended to have lower VO2 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.


 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.
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