Rodríguez-Gómez I, Martín-García M, García-Cuartero B, et al. - Using lean mass (LM) and percentage of fat mass (%FM) as mediator variables, researchers analyzed the impact of cardiorespiratory fitness (CRF) and muscle power output (MPO) on bone mass of prepubertal and pubertal children. The assumption was that during the sexual maturation period, both LM and %FM would be independent mediators of the relationships. Two hundred children [88 boys and 112 girls (11.5±2.0 years)] were analyzed in this investigation. While the independent mediator role of LM and %FM was present during the prepubertal stage in the associations between CRF or MPO and bone mass, only LM remained its mediator role in these relations during the postpubertal period. Therefore, the full effect of LM appears to increase with growth and sexual maturation, while the influence of %FM seems to disappear.