1 Original Article A Six-Year Exercise Program Improves Skeletal Traits without Affecting Fracture Risk – a Prospective Controlled Study in 2621 Children † Fredrik Detter MD, Björn E. Rosengren MD, PhD, Magnus Dencker* MD, PhD, Mattias Lorentzon** MD, PhD, Jan-Åke Nilsson BSc, PhD, Magnus K. Karlsson MD PhD Clinical and Molecular Osteoporosis Research Unit, Department of Clinical Sciences and Orthopedics, Lund University, and Department of Clinical Physiology*, Skåne University Hospital, SE-205 02 Malmö, Sweden ** Gothenburg University, Sahlgrenska University Hospital, Sweden Short title: Physical activity and accrual of bone mass and size during childhood. Correspondence: Fredrik Detter MD., Department of Orthopedics, Skåne University Hospital, SE - 205 02 Malmö, Sweden. Tel: +46 40 331000; Fax: +46 40 336200; Email: fredrik.detter@med.lu.se Abbreviations: bone mineral content (BMC), bone mineral density (BMD), 95% confidence interval (95% CI), counts per minute (counts/min or cpm), cross-sectional area (CSA), polar stress-strain index (polar SSI), dual X-ray absorptiometry (DXA), femoral neck (FN), Metabolic Equivalents (METs), moderate-to-vigorous physical activity (MVPA), Pediatric Osteoporosis Prevention (POP) Study, rate ratio (RR), standard deviations (SD), section modulus (Z), vigorous physical activity (VPA). Conflict of interest All authors have completed the Unified Competing Interest form at http://www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous six years, no other relationships or activities that could appear to have influenced the submitted work. † This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: [10.1002/jbmr.2168] Initial Date Submitted August 27, 2013; Date Revision Submitted December 18, 2013; Date Final Disposition Set December 21, 2013 Journal of Bone and Mineral Research © 2014 American Society for Bone and Mineral Research DOI 10.1002/jbmr.2168