1. From the Medical Research Council Epidemiology Unit, Cambridge, United Kingdom (UE, JL, and SB); the School of Health and Medical Sciences, Örebro University, Örebro, Sweden (UE); the Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway (SA and LBA); the Institute of Sport Science & Clinical Biomechanics, University of Southern Denmark, Odense, Denmark (LBA and KF); the