Results There was consistent evidence for a positive association between MF and physical activity .
For both MF components , there was support for objective ly measured physical activity , particularly for activity of vigorous intensity .
Sports participation was also consistently linked with both MF components , whereas the association with active transport was inconsistent .
For both MF components , associations with sedentary behaviors were inconsistent irrespective of measurement method , and the association between MF and sleep was considered uncertain .
Conclusions The available evidence supports a link between MF and physical activity , particularly for vigorous intensity activity and organized sports participation .
Background Muscular fitness ( MF ) is considered a powerful marker of health , but the extent to which common health behaviors are associated with MF during childhood and adolescence is currently unclear .
Objective We conducted a systematic review of studies investigating associations between MF ( i.e. , strength/power , local muscular endurance ) and physical activity , sedentary behaviors , and sleep in children and adolescents .
Cross-sectional and prospective associations between sleep, screen time, active school travel, sports/exercise participation and physical activity in children and adolescents
Background The aim of this study was to investigate how sleep , screen time , active school travel and sport and /or exercise participation associates with moderate-to-vigorous physical activity ( MVPA ) in nationally representative sample s of Norwegian 9- and 15-y-olds , and whether these four behaviors at age nine predict change in MVPA from age nine to 15 years . Method We pooled cross-sectional accelerometer and question naire data  from 9- ( n = 2366 ) and 15-y-olds ( n = 1554 ) that participated in the first ( 2005/06 ) and second ( 2011/12 ) wave of the Physical Activity among Norwegian Children Study to investigate cross-sectional associations . To investigate prospect i ve associations , we used data from a sub- sample that participated in both waves ( at age nine and 15 years , n = 517 ) . Results Cross-sectional analyses indicated a modest , inverse association between screen time and MVPA among 9- ( − 2.2 min/d ( 95 % CI : -3.1 , − 1.3 ) ) and 15-y-olds ( − 1.7 min/d ( 95 % CI : -2.7 , − 0.8 ) ) . Compared to their peers with 0–5 min/d of active travel to school , 9- and 15-y-olds with ≥16 min/d accumulated 7.2 ( 95 % CI : 4.0 , 10.4 ) and 9.0 ( 95 % CI : 3.8 , 14.1 ) more min/d of MVPA , respectively . Nine-y-old boys and 15-y-olds reporting ≥8 h/week of sports and /or exercise participation accumulated 14.7 ( 95 % CI : 8.2 , 21.3 ) and 17.9 ( 95 % CI : 14.0 , 21.8 ) more min/d of MVPA , respectively , than those reporting ≤2 h/week . We found no cross-sectional association between sleep duration and MVPA in either age group . None of the four behaviors predicted change in MVPA from age nine to 15 years ( p ≥ 0.102 ) . Conclusion Active travel to school and sport/exercise participation may be important targets for future interventions aim ed at increasing MVPA in children and adolescents . However , future studies are needed to determine causality
Results There was consistent evidence for a positive association between MF and physical activity .
For both MF components , there was support for objective ly measured physical activity , particularly for activity of vigorous intensity .
Sports participation was also consistently linked with both MF components , whereas the association with active transport was inconsistent .
For both MF components , associations with sedentary behaviors were inconsistent irrespective of measurement method , and the association between MF and sleep was considered uncertain .
Conclusions The available evidence supports a link between MF and physical activity , particularly for vigorous intensity activity and organized sports participation .
Background Muscular fitness ( MF ) is considered a powerful marker of health , but the extent to which common health behaviors are associated with MF during childhood and adolescence is currently unclear .
Objective We conducted a systematic review of studies investigating associations between MF ( i.e. , strength/power , local muscular endurance ) and physical activity , sedentary behaviors , and sleep in children and adolescents .