Ubago Guisado, EstherVlachopoulos, DimitrisFerreira de Moraes, Augusto CésarTorres Costoso, Ana IsabelWilkinson, Kelly MichelleMetcalf, Brad S.Sánchez Sánchez, JavierGallardo Guerrero, LeonorGracia Marco, Luis A.2019-10-142019-10-142017Ubago, E., Vlachopoulos, D., Ferreira, A. C., Torres, A., Wilkinson, K., Metcalf, B., ... & Gracia, L. (2017). Lean mass explains the association between muscular fitness and bone outcomes in 13‐year‐old boys. Acta Paediatrica, 106(10), 1658-1665. https://doi.org/10.1111/apa.139720803-52531651-2227http://hdl.handle.net/11268/8353Aim: This study investigated the associations between fitness indices and bone outcomes in young males. Methods: Data were collected between autumn and winter 2014–2015 on 121 males with a mean age of 13.1 ± 0.1 years: 41 swimmers, 37 footballers, 29 cyclists and 14 nonathletes. Participants were recruited from athletic clubs and schools across South West England. Lean mass, areal bone mineral density and hip structural estimates were measured using dual-energy X-ray absorptiometry. The relationships between bone outcomes and the vertical jump, standing long jump and the 20-m shuttle run test were analysed using three regression models: model 1 was adjusted by age and stature, model 2 added vigorous physical activity and model 3 then added lean mass. Results: The boys’ performance in the vertical jump and standing long jump was positively associated with the majority of bone outcomes in models 1 and 2, but most of these disappeared in model 3. The 20-m shuttle run test was positively associated with most bone outcomes in all three models. Lean mass played a key role in the association between muscular fitness and bone outcomes. Conclusion: Vigorous physical activity did not explain the associations between fitness and bone outcomes, but lean mass did.engjournal article10.1111/apa.13972restricted accessHuesosMotricidadMúsculosPediatríaDeporte