The relative decline in MVPA affects both sexes from an early age ; however , it is greater among girls .
Moderate-to-vigorous-intensity  physical activity ( MVPA )  is important for childhood obesity prevention and treatment , yet declines with age .
Timing and magnitude of the decline in MVPA in children and adolescents are unclear but important for informing effective obesity intervention development .
This systematic review aim ed to determine and compare the year-to-year changes in MVPA among children and adolescents .
Objectively measured physical activity and sedentary time: cross-sectional and prospective associations with adiposity in the Millennium Cohort Study
Objective To examine whether physical activity ( PA ) and sedentary time ( ST ) in primary school-aged children are associated with adiposity at the start of secondary school , and whether these associations differ by sex or ethnic group . Design Nationally representative prospect i ve cohort study . Setting Children born across the UK , between 2000 and 2002 . Participants 6497 singleton children . Outcome measures Measures of adiposity ( body mass index ( BMI ) , fat mass index ( FMI ) and fat free mass index (FFMI))—obtained at 7 and 11 years . Explanatory measures  Total daily PA ( mean counts per minute ( cpm ) ) ; minutes of moderate-to-vigorous PA ( MVPA ) ; and ST .  All assessed at 7 years using accelerometers . Results In cross-sectional analyses , total PA was inversely associated with FMI ( 3.7 % ( 95 % CI 2.7 % to 4.7 % ) reduction per 150 cpm increase ) , as was MVPA ( 4.2 % ( CI 3.2 % to 5.2 % ) reduction per 20 min/day increase ) . Associations were stronger in black and South Asian ethnic groups . Total PA and MVPA were not associated with FFMI . ST was positively associated with FMI ( 1.3 % ( CI 0.2 % to 2.3 % ) increase per 50 min/day increase ) and inversely associated with FFMI ( 0.5 % ( CI 0.2 % to 0.7 % ) reduction per 50 min/day increase ) . Longitudinally , MVPA at age 7 years remained inversely associated with FMI at age 11 years ( 1.5 % ( CI 0.4 % to 2.6 % ) reduction per 20 min/day increase ) . No association was found between total PA and ST and any of the later adiposity measures . Conclusions 7-year-old children who are more physically active are less likely to be obese at that age and at age 11 years . These associations were particularly evident in children from black or South Asian ethnicity at age 7 years and in boys at age 11 years . Measurements of fat mass provide valuable insights into ethnic differences in associations between adiposity and activity
The relative decline in MVPA affects both sexes from an early age ; however , it is greater among girls .
Moderate-to-vigorous-intensity  physical activity ( MVPA )  is important for childhood obesity prevention and treatment , yet declines with age .
Timing and magnitude of the decline in MVPA in children and adolescents are unclear but important for informing effective obesity intervention development .
This systematic review aim ed to determine and compare the year-to-year changes in MVPA among children and adolescents .