JIA is the most common chronic form of arthritis in children and affects at least 1 in 1000 Canadian children and youth. Current data suggests that a large number of children suffering from JIA will encounter permanent joint damage, to which direct effects of inflammation are an important contributor. Nevertheless, recent research has also shown that impaired muscle function and a subsequent alteration of joint loading might by itself induce joint damage. Fifty percent of JIA patients have significant impairments of muscle function and this is often present in patients who do not have active arthritis anymore. In addition to optimum medical treatment of the disease, it is therefore important to improve muscle function in order to protect the joints.