aExercise, Health and Performance Faculty Research Group bArthritis and Musculoskeletal Research Group, Discipline of Physiotherapy, Faculty of Health Sciences cCharles Perkins Centre, Sydney Medical School, University of Sydney, Lidcombe dNeuroscience and Muscle Research Group, The Children's Hospital at Westmead, Westmead ePaediatric Gait Analysis Service of New South Wales, Sydney Children's Hospitals Network, Randwick and Westmead, New South Wales, Australia fHebrew SeniorLife, Harvard Medical School gJean Mayer USDA Human Nutrition Research Centre on Aging, Tufts University, Boston, Massachusetts, USA.