Abstract: Three out of 16 identified studies met the inclusion criteria, with a total of 212 participants. All the included studies fulfilled at least seven of 10 methodological criteria. The outcome data of the following measures were homogenous and were pooled in a meta-analysis: functional ability (n = 198; WMD -0.07, 95% CI -0.22 to 0.08), quality of life (CHQ-PhS: n = 115; WMD -3.96, 95% CI -8.91 to 1.00) and aerobic capacity (n = 124; WMD 0.04, 95% CI -0.11 to 0.19). The results suggest that the outcome measures all favoured the exercise therapy but none were statistically significant. None of the studies reported negative effects of the exercise therapy. Overall, based on 'silver-level' evidence (www.cochranemsk.org) there was no clinically important or statistically significant evidence that exercise therapy can improve functional ability, quality of life, aerobic capacity or pain. The low number of available RCTs limits the generalisability. The included and excluded studies were all consistent about the adverse effects of exercise therapy; no short-term detrimental effects of exercise therapy were found in any study. Both included and excluded studies showed that exercise does not exacerbate arthritis. The large heterogeneity in outcome measures, as seen in this review, emphasises the need for a standardised assessment or a core set of functional and physical outcome measurements suited for health research to generate evidence about the possible benefits of exercise therapy for patients with JIA. Although the short-term effects look promising, the long-term effect of exercise therapy remains unclear.

Plain-language summary: The number of joints with pain was not measured in these studies. We often do not have precise information about side effects and complications. This is particularly true for rare but serious side effects. No short-term adverse effects of exercise therapy were found in the studies that make up this review. What is exercise therapy and what is JIA? Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic disease in children and is an important cause of short-term and long-term disability. In JIA the cause of the arthritis is unknown. It generally begins in children younger than age 16 years. It always lasts for at least six weeks. A physician will rule out other conditions that may be causing the symptoms before diagnosing JIA. Several types of exercise therapy are described in this review, for example, physical training programs such as strength training for improving muscle strength and endurance exercise for improving overall fitness (either land based or in a pool). Best estimate of what happens to children with JIA and exercise Ability to function: a child's ability to function changed less than 1 more point on a scale of 0 to 3. Other studies state that a change of 0.13 on the score of the Childhood Health Assessment Questionnaire (CHAQ) is a clinically important improvement from the perspective of children and their parents. This level of change has not been found in this review Quality of life: a child's quality of life changed between 2.5 and 4 more points on a scale of 1 to 50. There may be little or no difference with exercise. It is possible that these differences are the result of chance. Adverse effects: no short-term effects have been reported after exercise therapy for children with JIA.