1. Faculty of Health Promotion, Sport and Leisure Studies, School of Education, University of Iceland, Stakkahlid, 105 Reykjavik, Iceland
2. Faculty of Medicine, School of Health Sciences, University of Iceland, Laeknagardur 4th Floor, Vatnsmyrarvegur 16, 101 Reykjavik, Iceland
3. Department of Pediatrics, National University Hospital, Hringbraut, 101 Reykjavik, Iceland