1 1Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), Barcelona, Spain; 2Department of Health Sciences, Faculty of Earth and Life Sciences, VU University, Amsterdam, The Netherlands; 3Royal Netherlands Football Association, FIFA Medical Centre of Excellence, Zeist, The Netherlands; and 4CIBER Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain.