Ulf Ekelund1, Adrian Bauman2, I-Min Lee3. 1. Department of Sport Medicine, Norwegian School of Sport Sciences, Oslo 0806, Norway. Electronic address: ulf.ekelund@nih.no. 2. School of Public Health, Sydney University, Sydney, NSW, Australia. 3. Division of Preventive Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; Department of Epidemiology, Harvard T H Chan School of Public Health, Boston, MA, USA.