During exercise, energy comes mainly from carbohydrates and lipids. The relative contribution of lipids and glucose as energy substrates to exercise depends on the parameters of the exercise (duration, intensity and level of training) and the physiological conditions of the subject.

Inflammatory diseases such as juvenile idiopathic arthritis (JIA) are treated, for the most severe forms, by biotherapies. These treatments target certain pro-inflammatory cytokines including TNFα. In adults with rheumatoid arthritis several studies have shown that treatment with anti-TNFα increases insulin sensitivity. There is no data on the oxidation of energy substrates during exercise in children and adolescents with AJI, nor on the impact of anti-TNFα treatments on the oxidation of energetic substrates in children.

Investigators hypothesize that, compared to healthy children, children with JIA should exhibit altered oxidation of energy substrates at rest and submaximal physical exercise due to physical deconditioning and inflammation. In addition, those treated with anti-TNFα should have an oxidation profile of energy substrates at exercise different from that of patients not treated with anti-TNFα. Investigators also hypothesize that anti-TNFα treatments modify the contribution of energy chains (aerobic, anaerobic and anaerobic alactic) during the exercise.

Annual evaluation by Lipoxmax test and Wingate anaerobic test (WAnT) during 3 years or until the transition from pediatric to adult care.

For healthy volunteer, only one lipaxmax and Wingate test.

Inclusion Criteria:

• Children with juvenile idiopathic arthritis

Exclusion Criteria:

• active infection
• BMI > 25
• Systemic corticosteroid within last 3 months