Inclusion Criteria:  Confirmed diagnosis of JIA Polyarticular onset of JIA with bilateral involvement of the knee joint Age between 8 and 16 years Stable conditions (i.e., receive stable doses of medications in the past three months) Not participating in a regular exercise program in the past six months  Exclusion Criteria:  Fixed deformities History of joint surgery Ankylosing or fractures Bone destruction (erosive changes of the knee joint)