1 Institute Sport, Exercise and Health, Division of Surgery and Interventional Science, UCL, London, UK rweiler@doctors.org.uk.
2 Amsterdam Collaboration on Health and Safety in Sports, Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Centre Amsterdam, Amsterdam, Noord-Holland, The Netherlands.
3 The Football Association, St George's Park, Burton-upon-Trent, UK.
4 Fortius Clinic, London, UK.
5 University Hospitals Dorset NHS Foundation Trust, Poole Hospital, Poole, UK.
6 School of Sport, Health and Exercise Science, University of Portsmouth, Portsmouth, UK.