***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 Although school-based behavioral interventions for increasing physical activity ( PA ) in children and adolescents have been conducted , little evidence suggests that these curriculum-based approaches lead to increases in overall activity outside of program days . The overall goal of the " Active by Choice Today " ( ACT ) trial is to exp and the body of knowledge concerning the factors that influence long-term increases in PA in underserved adolescents ( low socioeconomic status , minorities ) during their middle school years . DESIGN AND SETTING An overview of the ACT study design , theoretical framework , process evaluation , and primary hypotheses is presented . The trial involves twenty-four middle schools ( 1560 6th grade rs ) in South Carolina that are r and omly assigned to one of two after-school programs ( motivational and life skills intervention , or general health education ) .  INTERVENTION The intervention integrates constructs from Self-Determination and Social Cognitive Theories to enhance intrinsic motivation and behavioral skills for PA . The intervention targets skill development for PA outside of program days and the after-school program social environment ( autonomy , choice , participation , belongingness , fun , enjoyment , support ) is design ed to positively impact cognitive mediators ( self-efficacy , perceived competence ) , and motivational orientation ( intrinsic motivation , commitment , positive self-concept ) . MAIN HYPOTHESES/ OUTCOMES : It is hypothesized that the 17-week motivational and life skills intervention will lead to greater increases in moderate-to-vigorous PA ( based on 7-day accelerometry estimates ) at post-intervention as compared to the general health education program . CONCLUSIONS Implication s of this innovative school-based trial are discussed BACKGROUND The purpose of this study was to examine the impact of the Pathways intervention on pychosocial variables related to physical activity and diet in American Indian children . METHODS Schools serving American Indian children were r and omized to a multicomponent intervention or control condition . At baseline ( fall of third grade ) and in the spring semester of third , fourth , and fifth grade s 755 boys and 692 girls completed a classroom-administered question naire . The question naire assessed self-efficacy , knowledge , and behavioral intentions related to diet and physical activity , as well as weight loss behaviors and body image . RESULTS Knowledge of nutrition and physical activity messages increased in both boys and girls in the intervention group compared to controls ; however , knowledge of which foods contained more fat did not increase consistently . Compared to controls , self-efficacy to be physically active increased among girls in intervention schools , but not among boys , whereas self-efficacy to make more healthy food choices did not increase more than in controls in either gender . In the intervention group , compared to controls , healthy food intentions and participation in physically active behaviors increased in both boys and girls . Perception of healthy body size and weight loss attempts did not differ in the intervention and control groups . CONCLUSION The Pathways intervention program had a positive impact on several aspects of obesity-related knowledge , attitudes , and behaviors Background : Youth may choose to be sedentary rather than physically active . Purpose : The purpose of this study was to use behavioral economics methods to investigate how experimental changes in the amount of sedentary behaviors influenced physical activity . Methods : Fifty-eight 8-to 16-year-old youth were studied in a within-subject crossover design with three 3-week phases : baseline , increasing , and decreasing targeted sedentary behaviors by 25 % to 50 % . Results : At baseline , boys were more active than girls ( 518.9 vs. 401.2 accelerometer counts/min , p = .02 ) , and obese youth more sedentary than nonobese youth ( 240.5 vs. 174.4 min/day , p = .003 ) . During the increase sedentary behavior phase , targeted sedentary behaviors increased by 52.1 % , with girls increasing sedentary behaviors more than boys ( 114.7 vs. 79.8 min/day , p = .04 ) . Physical activity decreased ( −48.3 counts/min , p < .01 ) when sedentary behaviors increased , with obese youth decreasing total and moderate to vigorous physical activity ( MVPA ) more than nonobese youth ( −110.4 vs. 8.9 counts/min , p < .001 ; −3.3 vs. −.03%MVPA , p = .013 ) . During the decrease sedentary behavior phase , targeted sedentary behaviors decreased by 55.6 % from baseline as nonobese youth increased physical activity , whereas obese youth decreased physical activity ( 55.8 vs. −48.0 counts/min , p = .042 ; 1.1 vs. −2.1 % MVPA , p = .021 ) . Youth who substituted physical activity when sedentary behaviors were increased had greater st and ardized body mass index ( z-body mass index = 1.4 vs. 0.4 , p = .018 ) , whereas youth who substituted physical activity when sedentary behaviors were decreased were less active at baseline ( 396.1 vs. 513.7 counts/min , p = .035 ) . Conclusions : Behavioral economics provides a methodology to underst and changes in physical activity when sedentary behaviors are modified and to identify factors associated with substitution of physically active for sedentary behaviors Background : Previous studies have shown that choice and self-initiated behavior change are important for increasing intrinsic motivation and physical activity ( PA )  , however , little of this research has focused on underserved adolescents . Purpose : This study examined the effects of a 4-week student-centered intervention on increasing PA  in underserved adolescents . Methods : Twenty-eight students in the intervention school were matched ( on race , percentage on free or reduced-price lunch program , gender , and age ) with 20 students from another school who served as the comparison group ( 30 girls , 18 boys ; ages 10–12 years ; 83 % African American ; 83 % on free or reduced-price lunch ) . The student-centered intervention was consistent with self-determination ( motivation ) theory and social cognitive theory in that it emphasized increasing intrinsic motivation and behavioral skills for PA . Intervention adolescents took ownership in selecting a variety of PA activities in which to participate , and they generated coping strategies for making effective PA behavior changes . Results : Intervention participants showed greater increases in accelerometer estimates of time spent in moderate PA , moderate-to-vigorous PA , and vigorous PA from baseline to Week 4 of the intervention than the comparison group . Intervention participants also showed greater increases in PA motivation and positive self-concept for PA than comparison adolescents . Conclusions : This study provides preliminary evidence that increasing adolescent involvement and choice of activities may be important in developing future PA interventions for underserved adolescents Strategic self-presentation ( motivational intervention [ MI ] ) is a theoretical approach that is distinct from social cognitive theory ( SCT ) . Specifically , strategic self-presentation involves increasing motivation by creating cognitive dissonance and inducing shifts in self-concept by generating positive coping strategies during a videotaped session . Fifty-three healthy African American adolescents were r and omized to a SCT + MI , SCT-only , or an education-only group  for increasing fruit and vegetable ( F&V ) intake and physical activity . The SCT + MI and SCT-only groups received a 12-week SCT program . Students in the SCT+ MI group also participated in a strategic self-presentation videotape session . Participants completed3-dayfoodrecords , completed measures of self-concept and self-efficacy , and wore an activity monitor for 4 days atpre- and posttreatment . Both the SCT+MI ( 2.6 ± 1.4vs . 5.7 ± 2.2 , p<. 05 ) and the SCT-only ( 2.5 ± 1.2 vs. 4.8 ± 2.4 , p < . 05 ) groups showed greater increases in F&V intake from pre-to posttreatment as compared with the education-only group ( 2.3 ± 1.0 , vs. 3.3 ± 2.1 , p > .05 ) . There were no significant time or group effects for any of the physical activity measures . Correlation analyses revealed that only the SCT + MI group showed that dietary self-concept ( r = .58,r = .67,p<.05 ) and dietary self-efficacy ( r = .65 , r = .85 , p < .05 ) were significantly correlated with posttreatment F&V intake and change in F&V intake , respectively . These findings suggest that the change in F&V intake in the SCT + MI group result ed from strategic self-presentation , which induced positive shifts in self-concept and self-efficacy BACKGROUND Enjoyment has been implicated as a determinant of physical activity among youth , but advances in underst and ing its importance have been limited by the use of measures that were not adequately vali date d. The present study examined : ( 1 ) the factorial validity of the  Physical Activity Enjoyment Scale ( PACES )  , and ( 2 ) the construct validity of PACES scores . METHODS Adolescent girls ( N=1797 ) , who were r and omly assigned to calibration ( n=899 ) and cross-validation ( n=898 ) sample s , completed the PACES and measures of factors influencing enjoyment of physical education , physical activity , and sport involvement . The factorial validity of the PACES and the measure of factors influencing enjoyment of physical education was tested using exploratory and confirmatory factor analysis . The hypothesized relationships among the measures were tested using structural equation modeling . RESULTS Unidimensional models fit the PACES and the measure of factors influencing enjoyment of physical education in the calibration and cross-validation sample s. The hypothesized relationships between the PACES and the measures of factors influencing enjoyment of physical education , physical activity , and sport involvement were supported in the entire sample , were similar in African-American and Caucasian girls , and were independent of physical fitness . CONCLUSIONS Evidence of factorial validity and convergent evidence for construct validity indicate that the PACES is a valid measure of physical activity enjoyment among adolescent girls , suitable for use as a mediator variable in interventions design ed to increase physical activity BACKGROUND Underst and ing the factors that influence physical activity behavior is important in the design of intervention programs targeted at youth . METHODS A prospect i ve study design was used to identify the predictors of vigorous physical activity ( VPA ) ( > or = 6 METs ) and moderate and vigorous physical activity ( MVPA ) ( > or = 3 METs ) among 202 rural , predominantly African-American children . Selected social-cognitive determinants of physical activity were assessed via question naire in the fifth grade . Participation in VPA and MVPA was assessed via the previous day physical activity recall 1 year later in the sixth grade . RESULTS For girls , participation in community sports , self-efficacy in overcoming barriers , enjoyment of school physical education , race ( white > black ) , and perception of mother 's activity level ( active vs inactive ) were significant predictors of VPA . For  MVPA , participation in community sports and self-efficacy in overcoming barriers were significant predictors . For boys , self-efficacy in overcoming barriers was the only significant predictor of VPA , while beliefs regarding activity outcomes and participation in community sports were significant predictors of MVPA . CONCLUSION Social-cognitive constructs such as physical activity self-efficacy , access to community physical activity outlets , and positive beliefs regarding physical activity outcomes are important predictors of future physical activity behavior among rural , predominantly African-American children The choice to be physically active or sedentary depends in part on the value of the alternatives that are available . The shift from sedentary to active alternatives may be a function of the value of the sedentary alternatives . To evaluate the influence of the value of the sedentary alternatives on the choice to be physically active or sedentary , 30 nonobese 8–12-year-old youth were r and omized in groups that provided a choice between 4 active alternatives or 4 sedentary alternatives ( Group 1 ) , their least valued sedentary activity ( Group 2 ) , or their most valued sedentary activity ( Group 3 ) , on computerized and question naire versions of a behavioral choice task . The computer task required participants to work for access to the alternatives . The work required to obtain access to the active alternatives remained constant for all choices , while the work required to gain access to the sedentary alternatives progressively increased . Compared to Groups 1 and 3 , participants in Group 2 chose to be sedentary less often as they had to make a choice between being physically active or sedentary on the computerized ( p < .005 ) and the question naire version ( p < .05 ) of the behavioral choice task , which correlated r = .54 , p < .01 . These results suggest interventions design ed to increase physical activity by reducing access to sedentary behaviors may need to consider the value of the targeted sedentary behavior and the extent to which the sedentary behaviors compete with physical activity Background . Obesity has become the most common pediatric chronic disease in the modern era . Early prevention and treatment of childhood and adolescent obesity is m and ated . Surprisingly , however , only a minor fraction of obese children participate in weight reduction interventions , and the longer-term effects of these weight-reduction interventions among children have not been eluci date d. Objective . To examine prospect ively the short- and long-term effects of a 3-month , combined dietary-behavioral-physical activity intervention on anthropometric measures , body composition , dietary and leisure-time habits , fitness , and lipid profiles among obese children . Methods . In this r and omized prospect i ve study , 24 obese subjects completed the 3-month intervention and were compared with 22 obese , age- and gender-matched , control subjects . Results . At 3 months 
    Output:
    
In conclusion , physical activity intervention programs may improve self-efficacy  in youths .
Further research is needed to quantify the association of self-efficacy ratings after completing physical activity interventions with objective health improvements , such as weight loss