1 Department of Pediatrics, University of Alberta, Edmonton, Alberta T6G 1C9, Canada.
2 Institute of Sport, Physical Activity and Leisure, Centre of Active Lifestyles, Carnegie Faculty, Leeds Beckett University, Headingley Campus, Leeds LS6 3QS, United Kingdom.
3 Harvard Medical School, Harvard University, Boston, Massachusetts 02115.
4 Department of Pediatrics, Wake Forest School of Medicine & Brenner Children's Hospital, Brenner FIT (Families in Training), Winston-Salem, North Carolina 27157.