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 .
Intervention effects on physical activity: the HEIA study - a cluster randomized controlled trial
Background Although school-based interventions to promote physical activity in adolescents have been suggested in several recent review s , questions have been raised regarding the effects of the strategies and the methodology applied and for whom the interventions are effective . The aim of the present study was to investigate effects of a school-based intervention program : the HEalth in Adolescents ( HEIA ) study , on change in physical activity , and furthermore , to explore whether potential effects varied by gender , weight status , initial physical activity level and parental education level . Methods This was a cluster r and omized controlled 20 month intervention study which included 700 11-year-olds . Main outcome -variable was mean count per minute ( cpm ) derived from ActiGraph accelerometers ( Model 7164/GT1 M ) . Weight and height were measured objective ly . Adolescents reported their pubertal status in a question naire and parents reported their education level on the consent form . Linear mixed models were used to test intervention effects and to account for the clustering effect of sampling by school . Results The present study showed an intervention effect on overall physical activity at the level of p = 0.05 with a net effect of 50 cpm increase from baseline to post intervention in favour of the intervention group ( 95 % CI −0.4 , 100 ) . Subgroup analyses showed that the effect appeared to be more profound among girls ( Est 65 cpm , CI 5 , 124 , p = 0.03 ) and among participants in the low-activity group ( Est 92 cpm , CI 41 , 142 , p < 0.001 ) , as compared to boys and participants in the high-activity group , respectively . Furthermore , the intervention affected physical activity among the normal weight group more positively than among the overweight , and participants with parents having 13–16 years of education more positively than participants with parents having either a lower or higher number of years of education . The intervention seemed to succeed in reducing time spent sedentary among girls but not among boys . Conclusions A comprehensive but feasible , multi-component school-based intervention can affect physical activity patterns  in adolescents by increasing overall physical activity . This intervention effect seemed to be more profound in girls than boys , low-active adolescents compared to high-active adolescents , participants with normal weight compared to the overweight , and for participants with parents of middle education level as opposed to those with high and low education levels , respectively . An implementation of the HEIA intervention components in the school system may have a beneficial effect on public health by increasing overall physical activity among adolescents and possibly among girls and low-active adolescents in particular
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 .