In children with JIA, a single 20-minute exercise bout at 70% of maximal heart rate at 8:30 am induced a slight transient increase in the level of plasma calprotectin (MRP 8/14, a pro-inflammatory polypeptide), together with transient self-evaluated pain, but no significant change in IL-6 or soluble IL-6 receptors (31). This evidence concerns the gene IL6 and juvenile idiopathic arthritis.