Four forceplates will be used to measure kinetic data and static balance. Postural stability testing will be performed on all subjects (Figure 4). We will evaluate responses to dynamic stability challenges that investigates motor and sensory control and adaptation to perturbations. Static (quiet standing) postural stability tests will be done on all subjects. A licensed physical therapist (PT) will perform the exam following the protocol of the Shriners Hospital for Children's motion lab.