Can fitness testing promote physical activity in adolescents with juvenile idiopathic arthritis?

Physical activity (PA) is important for disease management and overall health in adolescents with juvenile idiopathic arthritis (JIA). In clinical practice, identifying low cardiorespiratory fitness (CRF) and encouraging higher-intensity PA are priorities. We investigated whether introducing submaximal treadmill fitness testing could increase PA, estimated peak oxygen uptake (VO_2peak), walking distance, physical function, and health-related quality of life (HRQoL) in adolescents with JIA, and examined associations between PA, VO_2peak, and walking distance.

In this exploratory pre-post study, adolescents aged 10-18 years with non-systemic JIA were consecutively recruited during routine physiotherapy visits at a rheumatology clinic. A submaximal treadmill test was used to estimate VO_2peak at baseline and follow-up. Self-reported PA was assessed with the International Physical Activity Questionnaire Short-Form (IPAQ-SF), and physical function and HRQoL with the Juvenile Arthritis Multidimensional Assessment Report (JAMAR). Within-participant changes were analysed with paired tests; associations were assessed using Spearman's rank correlation.

Thirty-four participants were included; 24 completed follow-up. IPAQ-derived PA did not change significantly between assessments. Estimated VO_2peak was higher at follow-up by 2.4 (SD 4.4) mL∙kg^- 1∙min^- 1 (P = 0.01) and walking distance was higher by 31 (69) metres (P = 0.04), whereas no significant changes were observed in JAMAR physical function or HRQoL. Vigorous PA showed the strongest associations with estimated VO_2peak at baseline and follow-up (rho up to 0.51; P < 0.05). Associations of moderate-to-vigorous and total PA with VO_2peak were weaker and evident only at follow-up (rho ~ 0.41-0.43), and vigorous PA correlated with walking distance at follow-up (rho = 0.42; P = 0.040); other associations were low or non-significant.

Introducing submaximal treadmill fitness testing in routine care did not change self-reported PA, but estimated VO_2peak and walking distance increased significantly. Submaximal testing may be a feasible clinical tool to identify low CRF and support counselling. Larger studies are needed to determine whether fitness testing can promote PA and to identify which adolescents benefit most, using measurement approaches that capture complementary aspects of PA (e.g., self-report for context and perceived behaviour, and device-based metrics for volume and intensity where appropriate).