1. Institute for Neuroscience and Muscle Research; The Children's Hospital at Westmead; Westmead Australia
2. Discipline of Physiotherapy, Faculty of Health Sciences; The University of Sydney; Lidcombe Australia
3. Paediatric Gait Analysis Service of New South Wales; Sydney Children's Hospitals Network (Randwick and Westmead); Sydney Australia
4. Discipline of Exercise and Sport Science, Faculty of Health Sciences; The University of Sydney; Lidcombe Australia
5. Sydney Medical School & Charles Perkins Centre; The University of Sydney; Camperdown Australia
6. Hebrew Senior Life, and Jean Meyer USDA Human Nutrition Research Center on Aging; Tufts University; Boston MA 02111 USA
7. T.Y. Nelson Department of Neurology & Neurosurgery; The Children's Hospital at Westmead; Westmead Australia