***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: Background This study aim ed to evaluate the associations of selected demographic , individual , social , and environmental factors with moderate-to-vigorous physical activity ( MVPA ) in a sample of children and adolescents . Methods  MVPA  was assessed among youth ( n = 294 ) 10 - 17-years-old using the ActiGraph accelerometer . Youth completed measures of demographic and individual variables related to physical activity ( PA ) , perceived social support by parents and peers , and perceived neighborhood characteristics . Parents completed the long-form of the International Physical Activity Question naire . The Physical Activity and Media Inventory was used to measure the home environment and Geographical Information Systems software was used to measure the physical neighborhood environment . Bivariate correlations and hierarchical multiple regression were conducted stratified by gender . Results Boys participated in significantly more MVPA than girls . In hierarchical analyses , peer support , home PA equipment , and temperature were significantly associated with MVPA among boys whereas distance to the school they attended was associated with MVPA among girls . The final models accounted for 25 % and 15 % of the variance in MVPA among boys and girls , respectively . Conclusions Important differences exist among the individual , social , and environmental factors related to MVPA between boys and girls . Boys ' levels of activity appear to be influenced by factors closely linked to unstructured and social types of activities whereas girls ' activities relate to internal and external barriers as well as their proximity to their schools . The prospect i ve contribution of these important individual , social , and environmental factors to changes in MVPA among children and adolescents remains to be determined 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 To test whether self-efficacy for overcoming barriers to physical activity has direct , indirect ( i.e. , mediated ) , or moderating relations with naturally occurring change in perceived social support and declines in physical activity during high school . METHODS Latent growth modeling was used with measures completed in the 8th , 9th , and 12th grade s by a cohort of 195 Black and White girls . RESULTS Self-efficacy was stable and moderated the relation between changes in physical activity and perceived social support . Girls who maintained a perception of strong social support had less of a decline in physical activity if they also had high self-efficacy . However , girls having high self-efficacy had a greater decline in physical activity if they perceived declines in social support . CONCLUSIONS R and omized controlled trials of physical activity interventions based on social cognitive theory should consider that the influence of girls ' perceptions of social support on their physical activity may differ according to their efficacy beliefs about barriers to physical activity OBJECTIVE To identify factors associated with changes in physical activity in adolescent girls at risk for sedentary lifestyles and obesity . DESIGN A cohort study was performed with 201 high school girls recruited to participate in an evaluation study of a school-based obesity prevention physical education program . Three assessment s were performed during an 8-month period . MAIN OUTCOME MEASURES Associations between physical activity and a range of personal factors ( self-acceptance , self-worth , athletic competence , body image , depressive mood , perceived benefits , enjoyment of physical activity , self-efficacy , and body mass index ) , behavioral factors ( watching television and time constraints )  , and socioenvironmental factors ( social support and costs/re sources )  were assessed . RESULTS The 2 strongest and most consistent factors associated with change in physical activity were time constraints and support for physical activity from peers , parents , and teachers . Measures assessing self-perceptions , global ( ie , self-worth ) and specific to physical activity ( ie , self-efficacy to be physically active ) , were also associated with change in physical activity . For example , a decrease of 2.0 U for an adolescent 's perceived time constraints ( possible range , 3.0 - 12.0 U ) would be expected to lead to an increase of 53 minutes of moderate to vigorous physical activity per week ( 95 % confidence interval , 33 - 72 minutes ) . An increase of 2.0 U in perceived support for physical activity ( possible range , 3.0 - 12.0 U ) would be expected to lead to an increase of 35 minutes of moderate to vigorous physical activity per week ( 95 % confidence interval , 13 - 56 minutes ) . An increase of 3.0 U on the self-worth scale ( possible range , 5.0 - 20.0 U ) might be expected to lead to an increase of 19 minutes of moderate to vigorous physical activity per week ( 95 % confidence interval , 0 - 40 minutes ) . CONCLUSION The effectiveness of interventions aim ed at increasing physical activity among adolescent girls might be enhanced by engaging support from friends , family , and caring adults ; addressing real and perceived time constraints ; and helping adolescent girls feel more confident about themselves and their ability to engage in physical activity OBJECTIVE : To test the feasibility of creating a valid and reliable checklist with the following features : appropriate for assessing both r and omised and non-r and omised studies ; provision of both an overall score for study quality and a profile of scores not only for the quality of reporting , internal validity ( bias and confounding ) and power , but also for external validity . DESIGN : A pilot version was first developed , based on epidemiological principles , review s , and existing checklists for r and omised studies . Face and content validity were assessed by three experienced review ers and reliability was determined using two raters assessing 10 r and omised and 10 non-r and omised studies . Using different raters , the checklist was revised and tested for internal consistency ( Kuder-Richardson 20 ) , test-retest and inter-rater reliability ( Spearman correlation coefficient and sign rank test ; kappa statistics ) , criterion validity , and respondent burden . MAIN RESULTS : The performance of the checklist improved considerably after revision of a pilot version . The Quality Index had high internal consistency ( KR-20 : 0.89 ) as did the subscales apart from external validity ( KR-20 : 0.54 ) . Test-retest ( r 0.88 ) and inter-rater ( r 0.75 ) reliability of the Quality Index were good . Reliability of the subscales varied from good ( bias ) to poor ( external validity ) . The Quality Index correlated highly with an existing , established instrument for assessing r and omised studies ( r 0.90 ) . There was little difference between its performance with non-r and omised and with r and omised studies . Raters took about 20 minutes to assess each paper ( range 10 to 45 minutes ) . CONCLUSIONS : This study has shown that it is feasible to develop a checklist that can be used to assess the method ological quality not only of r and omised controlled trials but also non-r and omised studies . It has also shown that it is possible to produce a checklist that provides a profile of the paper , alerting review ers to its particular method ological strengths and weaknesses . Further work is required to improve the checklist and the training of raters in the assessment of external validity The aim of this study was to examine modifiable biological , psychological , behavioral and social-environmental correlates of physical activity among 1129 Norwegian 11-year-old children within a cross-sectional sample from the HEalth In Adolescents study .  Physical activity was assessed by accelerometer , and weight and height were measured objective ly . Age- and gender-specific cut-off points proposed by the International Obesity Task Force were used to define body mass index . Social-environmental variables were self-reported by question naire . Hierarchical regression ( linear mixed models ) revealed that normal weight children scored higher on percentage daily moderate-to-vigorous physical activity [ % daily moderate to vigorous physical activity ( MVPA ) ] than overweight/obese children ( P<0.001 ) . Self-efficacy ( P<0.01 ) and perceived social support from friends ( P<0.01 ) were positively associated with children 's % daily MVPA , and a negative association was found for computer/game-use on weekends ( P<0.01 ) . A moderator effect of weight category ( normal vs overweight/obese ) in the relationship between computer/game-use on weekends and % daily MVPA was detected ( P<0.05 ) , reflecting that higher computer/game-use on weekends was associated with lower % MVPA among the overweight/obese , but not among the normal weight . Modifiable correlates from multiple domains accounted for 14 % of the variance in % daily MVPA . Prospect i ve and intervention studies are needed to examine whether these factors act as mediators for physical activity change in pre-adolescent children OBJECTIVE This study examined differences in ( 1 ) psychosocial correlates of physical activity and in ( 2 ) physical activity within different context s and sedentary behaviors between normal weight and overweight adolescents . It further explored whether the prediction of physical activity by the psychosocial correlates is different in normal weight and overweight adolescents . RESEARCH METHODS AND PROCEDURE A community sample of 6078 11 to 19 year olds from 38 secondary schools , which were r and omly selected throughout the country , completed a vali date d computerized question naire about physical activity , sedentary behaviors , and psychosocial correlates . Differences in mean scores on the psychosocial correlates and on the self-rated physical activity were analyzed between the normal weight ( n=5563 ) and the overweight ( n=515 , 8.5 % ) group . RESULTS This study showed that overweight adolescents do less intense physical activities ( p<0.001 ) and have less favorable psychosocial correlates related to physical activity ( p<0.001 ) than their normal weight counterparts . However , the strength of the associations between psychosocial variables and total physical activity were comparable in overweight and normal weight adolescents . More support from family and friends , more fun in physical activity , higher self-efficacy , the perception of more competition benefits , and the perception of less lack of interest were all associated with higher total levels of physical activity . The results suggest that no specific tailoring on psychosocial correlates of physical activity is necessary for overweight adolescents compared with normal weight ones . DISCUSSION Both overweight and normal weight adolescents can be approached by interventions focusing on the same psychosocial variables to increase physical activity The present study examined whether self-efficacy mediates the relationship between family social influence and physical activity among youth who have experienced a recent lapse in their physical activity participation . Using a prospect i ve , longitudinal design , participants completed measures of social influence , self-regulatory efficacy and physical activity .  Only those participants whose physical activity declined were retained for further analysis . Self-regulatory efficacy partially mediated the relationship between family social influence and physical activity , with self-efficacy mediating 36 percent of the total effect . The results provide support for self-regulatory efficacy as a mediator and provide preliminary insight into the potential mechanisms for preventing lapses in activity from developing into prolonged periods of inactivity within this population OBJECTIVE To determine if perceptions of the social and physical environment are associated with active transport and leisure-time sports among Belgian youth and to investigate if this relationship is moderated by self-efficacy . METHODS In February-May 2008 , 1445 adolescents ( 17.4+/-0.6 yrs ) were recruited in 20 r and omly selected Belgian schools .  Physical activity , psychosocial , and environmental factors were assessed using vali date d question naires . Moderated multilevel regression analysis was used to examine the association between physical activity and possible correlates . RESULTS Social environmental variables  ( modeling and social support ) were positively associated with active transportation and leisure-time sports ( p<0.05 ) . Higher l and use mix diversity , higher street connectivity , more attractive environments 
    Output:
    
Social support was positive and consistently associated with the physical activity level of adolescents in cross-sectional and longitudinal studies .
Those who received more overall social support  as well as support from both parents , friends and family showed higher levels of physical activity .