1. Department of Public Health and Policy, University of Liverpool, Liverpool, United Kingdom;
2. Department of Children's Orthopaedic Surgery, Alder Hey Hospital, Liverpool, United Kingdom;
3. Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom;
4. School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, Australia;
5. School of Medicine, University of Liverpool, Liverpool, United Kingdom;
6. Norwich Medical School, University of East Anglia, Norwich, United Kingdom; and
7. Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom