1. Department of Sports Medicine, The Norwegian School of Sport Sciences, Oslo, Norway.
2. Oslo Centre for Biostatistics and Epidemiology, Oslo University Hospital, Oslo, Norway.
3. Department of Physical Performance, The Norwegian School of Sport Sciences, Oslo, Norway.
4. Department of Paediatrics, Haukeland University Hospital, Bergen, Norway.
5. Paediatric Oncology/Haematology, University Children's Hospital Basel, Basel, Switzerland.
6. Childhood Cancer Research Group, Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
7. Division for Paediatric- and Adolescence Medicine, Department of Paediatric Haematology and Oncology, Oslo University Hospital, Oslo, Norway.
8. Institute for Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.