We propose conducting a controlled trial investigation. This implies, that one group of study participants, called the intervention group, will do the WBV therapy, whereas a second group, called the control group, will just follow their daily habitual activities. All participants will have an initial assessment of muscle function, electrical muscle activity and joint biomechanics by completely painless measurement techniques at the Children's Hospital of Eastern Ontario (CHEO) and a nearby Human Motion Biomechanics lab at the University of Ottawa. In addition, an MRI of the lower legs without contrast media will be done to confirm the absence of joint effusions as well as bone or muscle edema. Quality of life will be assessed by a standard questionnaire that has been validated in JIA. Subsequently, study participants in the intervention group as well as their parents will be introduced to the therapy during two separate sessions at the CHEO. They will then take a WBV device home and perform 6 minutes of training on 5 days a week for 3 months. Each month, they will return to CHEO for assessment of muscle function and demonstration of training technique. At the end of the 3 month period, both intervention and control group patients will repeat the initial set of assessments including MRI. After another 3 month period, all participants will return for a final assessment of muscle function and joint biomechanics but not MRI to document persistence of any change observed.