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[Background]: The combined effect of cardiorespiratory fitness (CRF) and body mass index (BMI) on cardiovascular disease (CVD) risk in young people remains to be fully determined. We examined the individual and combined associations of CRF and BMI with clustered CVD risk factors, and the mediator role of BMI in the association between CRF and clustered CVD risk factors in children and adolescents., [Methods]: 237 children (111 girls) and 260 adolescents (120 girls) were included in this cross‐sectional study. Height and weight were assessed and BMI was calculated. A CVD risk factor index (CVDRF‐I) was computed from: waist circumference, systolic blood pressure, triglycerides, high‐density lipoprotein cholesterol and glucose. CRF was assessed using the 20‐m shuttle run test. Regression analysis, analysis of covariance and mediation analysis (Baron and Kenny procedures) were used to test the independent and combined effect of CRF and BMI on CVDRF‐I, and to test mediation hypothesis, respectively., [Results]: CRF was negatively associated with CVDRF‐I (all P, [Conclusions]: BMI is an independent predictor of CVDRF‐I and a mediator of the association between CRF and CVDRF‐I in children and adolescents. These results help to clarify the associations between CRF, weight status and cardiovascular health, suggesting that future CVD health would benefit from maintaining an optimal weight status., This work was supported by the National Plan for Research, Development and Innovation (R + D + i) from the Spanish Ministry of Science and Innovation [DEP 2010‐21662‐C04‐00 (DEP 2010‐21662‐C04‐01: DEP 2010‐21662‐C04‐02: DEP 2010‐21662‐C04‐03: DEP 2010‐21662‐C04‐04)]; and by the Spanish Ministry of Education [FPU15/05337]. IEC is supported by a grant from the Alicia Koplowitz Foundation.

The study aimed (a) to examine changes in physical activity (PA) during the whole day, school hours, recess, and physical education classes (PEC) during a 2‐year period in primary and secondary students; (b) to identify changes in the proportion of compliance with specific PA recommendations for these periods; and (c) to examine whether PA levels at baseline are associated with PA levels 2 years later. Eight hundred and fourteen (51.8% boys) children and 658 (50.1% boys) adolescents from 41 Spanish schools participated in the study. Hip‐worn accelerometers were used to assess PA during different time periods. Light PA (LPA) declined during the whole day, school hours, recess (all P < 0.001, except child girls for recess), and PEC (all, P < 0.05) in children and adolescents. Moderate‐to‐vigorous PA (MVPA) during the whole day and recess declined in child boys (P < 0.01 and P < 0.001, respectively) and adolescent boys (P < 0.001 and P < 0.05, respectively). MVPA during PEC declined in adolescent boys (P < 0.001) and adolescent girls (all P < 0.05). The proportion of compliance with the specific PA recommendations for these periods declined (P < 0.05), except for PEC in adolescent girls. PA during the whole day at baseline was moderately associated with PA during the whole day years later (ICCs = 0.210‐0.544, with one exception), but this association was lower for the school‐based PA. In conclusion, time spent in MVPA and LPA during the whole day and recess declined over time in child and adolescent boys and during PEC in adolescents. These findings highlight the need to promote PA interventions in these settings., This study was supported by the DEP 2010‐21662‐C04‐00 (DEP 2010‐21662‐C04‐01: DEP 2010‐21662‐C04‐02: DEP 2010‐21662‐C04‐03: DEP 2010‐21662‐C04‐04) grant from the Spanish National Plan for Research, Development and Innovation (R+D+i), MICINN. The Spanish Ministry of Economy, Industry and Competitiveness awarded a "Juan de la Cierva" postdoctoral grant to the author DSO (FJCI‐2015‐25867) and a “Ramón y Cajal” postdoctoral grant to the author DMG (RYC‐2016‐20546). VCS was supported by an FPI grant from the Autonomous University of Madrid. AGC is grateful to the "Program to promote and boost research activity" of the University of Cádiz for the granting of a mobility aid.