***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE : To identify correlates of objective ly measured moderate and vigorous physical activity ( MVPA ) in children during preschool attendance . METHODS : This cross-sectional study included data from 426 apparently healthy Danish children ( 49.5 % boys ) , 5 to 6 years of age enrolled in 42 r and omly selected preschools . The percentage of time spent in MVPA ( ≥574 counts/15 second ) during preschool attendance was measured using ActiGraph accelerometers over 4.3 preschool days in May and June in 2009 . Thirty-seven potential correlates across the child , preschool staff , and preschool environment domains were tested for associations with MVPA . RESULTS : The final multivariate model identified 9 significant correlates of MVPA . Preterm birth , vegetation on the playground , and rainy days were negatively associated with MVPA , whereas child motor coordination , location of preschool building on the playground , gender ( boys ) , percentage afternoon hours , and size of indoor area per child were positively associated with MVPA . The direction of the significant association with the parental mean education level was unclear . CONCLUSIONS : We identified a number of new modifiable correlates  of MVPA  during preschool attendance . The positive association with size of indoor area per child and location of the preschool building on the playground seem important correlates to be targeted in future studies BACKGROUND Underst and ing the determinants of physical activity in children is critical for the treatment and prevention of childhood obesity . Social-cognitive theory has been used to underst and behavioral patterns in children . OBJECTIVES To explore the relationship between health beliefs , self-efficacy , social support , and sedentary activities and physical  activity levels in children and to examine the relationship between physical activity and  children 's  self-esteem . METHODS Ninety-two children aged 10 to 16 years completed the study .  Physical activity was monitored for 1 week with a motion detector ( Actitrac ; IM Systems , Baltimore , Md ) . Moderate-level activity and high-level activity were defined based on the results of treadmill testing . Health beliefs , self-efficacy , social influences , and time spent in sedentary behaviors were determined through question naires . Self-esteem was measured using the Piers-Harris Children 's Self-Concept Scale . Chronic anxiety was measured with the Revised Children 's Manifest Anxiety Scale . RESULTS There was a significant decline in physical activity levels between ages 10 and 16 years , particularly in girls . Preteen girls spent approximately 35 % more time in low- and high-level activity than did teenage girls ( P<.001 ) . Overall , children spent 75.5 % of the day inactive , with a mean + /- SD of 5.2 + /- 1.8 hours watching television , sitting at the computer , and doing homework . In contrast , only 1.4 % of the day ( 12.6 + /- 12.2 minutes ) was spent in vigorous activity . Time spent in sedentary behaviors was inversely correlated with the amount of moderate-level activity ( P<.001 ) but not high-level activity . In contrast , time spent in high-level activity correlated with self-efficacy scores ( P<.001 ) and social influences scores ( P<.005 ) . High-level physical activity was also associated with improved self-esteem ( P<.05 ) . Higher health beliefs scores were not correlated with physical activity levels . CONCLUSIONS Children and adolescents are largely sedentary . Correlates of high- and low-level physical activity are different . Time spent on sedentary activities is inversely correlated with moderate-level activity , while self-efficacy and social influences are positively correlated with more intense physical activity . In addition , increased high-level physical activity is an important component in the development of self-esteem in children OBJECTIVE This study compared correlates of  physical activity ( PA )  among African-American and white girls of different weight groups to guide future interventions . RESEARCH METHODS AND PROCEDURES Participants were 1015 girls ( mean age , 14.6 years ; 45 % African-American ) from 12 high schools in South Carolina who served as control subjects for a school-based intervention .  Post-intervention measures obtained at the end of ninth grade were used . PA was measured using the Three-Day PA Recall , and a question naire measured social-cognitive and environmental variables thought to mediate PA . Height and weight were measured , and BMI was calculated . Girls were stratified by race and categorized into three groups , based on BMI percentiles for girls from CDC growth charts : normal ( BMI < 85th percentile ) , at risk ( BMI , 85th to 94th percentile ) , and overweight ( BMI > or = 95th percentile ) . Girls were further divided into active and low-active groups , based on a vigorous PA st and ard ( average of one or more 30-minute blocks per day per 3-day period ) . Mixed-model ANOVA was used to compare factors among groups , treating school as a r and om effect RESULTS None of the social-cognitive or environmental variables differed by weight status for African-American or white girls . Perceived behavioral control and sports team participation were significantly higher in girls who were more active , regardless of weight or race group . In general , social-cognitive variables seem to be more related to activity in white girls , whereas environmental factors seem more related to activity in African-American girls . DISCUSSION PA interventions should be tailored to the unique needs of girls based on PA levels and race , rather than on weight status alone The decline in physical activity with age may be the most consistent finding in physical activity epidemiology . Although this phenomenon is well accepted , it is not well understood . The purpose s of this symposium are to determine whether there are critical periods of decline and quantify sex differences in the decline . Data from cross-sectional and prospect i ve studies indicate the decline is steepest between the ages of 13 and 18 . The decline is generally greater for male than female subjects , and the decline varies by type and intensity of the activity . A review of animal studies documented the age-related decline in many species . This suggests a biological basis , and a probable mechanism is the dopamine system that regulates motivation for locomotion . The decline in  physical activity  with age is antithetical to public health goals , so methods of countering the decline need to be developed , based upon an improved underst and ing of the phenomenon and its causes 
    Output:
    
Research demonstrated that peers and friends have an important role to play in the physical activity behavior of adolescents .
Six processes were identified through which peers and /or friends may have an influence on physical activity including : peer and /or friend support , presence of peers and friends , peer norms , friendship quality and acceptance , peer crowds , and peer victimization .