1. D. Shirley, PT, PhD, FACP, is Coordinator of Musculoskeletal Physiotherapy, Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia.
2. H.P. van der Ploeg, PhD, is Senior Research Fellow, Cluster for Physical Activity and Health, Sydney School of Public Health, University of Sydney, Level 2, Medical Foundation Building (K25), Sydney, New South Wales 2006, Australia.
3. A.E. Bauman, PhD, FAFPHM, is Sesquicentenary Professor of Public Health (Behavioral Epidemiology and Health Promotion), Cluster for Physical Activity and Health, Sydney School of Public Health, University of Sydney.