***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 The physical activity ( PA ) levels of many children and adolescents in Australia are currently insufficient to promote health benefits . Physical education ( PE ) programs aim to promote PA and reach nearly all school-aged children , but PA levels within PE lessons are often low . PE teachers may influence children ’s motivation to be physically active in PE lessons , but little is known about teacher strategies that effectively motivate children to participate in PA , and few intervention studies have examined motivational strategies in PE . The purpose of this study was to compare the effect of three motivational strategies , each based on Self-Determination Theory ( SDT ) , on PA levels , and their hypothesized antecedents , during year 8 PE lessons . Methods / design This study employed a cluster-r and omized controlled trial design . Following a familiarization session , PA levels and hypothesized PA antecedents were measured during a baseline lesson and a post-intervention or control lesson .  Teachers ( n = 16 ) and their classes from five secondary schools in Sydney , Australia were r and omly assigned into four blocks and instructed to provide one of four 20-min lesson teaching strategy conditions : ( 1 ) explaining the relevance of activities ; ( 2 ) providing choice from PA options selected by the teacher ; ( 3 ) providing equipment and free choice of activities ; or ( 4 ) usual practice . The primary outcomes were lesson time spent in moderate-to-vigorous PA , and motivation towards the lesson . Secondary outcomes were perceptions of teacher behavior , psychological needs satisfaction , and lesson time spent in sedentary behavior . PA and sedentary behavior were measured during baseline and post-intervention lessons with waist-mounted Actigraph GT3X accelerometers . Teacher behavior , psychological needs satisfaction , and motivation were assessed via question naires at the end of each lesson . Linear mixed-model analyses will be run on all outcomes , with students nested within teachers as a r and om effect . Discussion Study findings will inform the development of effective SDT-based teaching strategy interventions to enhance students ’ psychological needs satisfaction , motivation , and PA levels . More effective teaching strategies may be identified that are capable of improving  adolescents ’ PA levels , and thereby provide beneficial population health outcomes .Trial registration This trial is registered with Current Controlled Trials and is traceable as IS RCT N07038258 BACKGROUND It is unclear how moderate and vigorous intensities of physical activity ( PA ) are associated with cardiovascular fitness ( CVF ) and percentage of body fat ( % BF ) in adolescents . OBJECTIVE We tested the hypothesis that vigorous PA , to a greater degree than moderate PA , would be associated with better CVF and lower % BF . DESIGN This was a cross-sectional study of 421 black and white high school students ( x age : 16 y ) .  PA was measured with 5 d of accelerometry and expressed in min/d of moderate or vigorous PA .  CVF was measured with a multistage treadmill test and was expressed as the oxygen consumption at a heart rate of 170 bpm . % BF was measured with dual-energy X-ray absorptiometry . Multiple regressions were used to determine the degree to which variance in CVF and % BF was explained by PA , after control for age , sex , race , and the sex x race interaction . RESULTS A higher index for CVF was associated with higher amounts of moderate and vigorous PA ;  more variance was explained by vigorous than by moderate PA .  Lower % BF was associated with higher amounts of vigorous PA but not with the amount of moderate PA . CONCLUSION Black and white adolescents who engaged in relatively large amounts of free-living vigorous exercise were likely to be relatively fit and lean This study examined the effectiveness of an intervention to increase  levels of moderate-to-vigorous intensity physical activity ( MVPA )  during girls ' physical education lessons . Two Year 7 classes ( age 11 - 12 years ) were r and omly appointed to control and experimental groups . Both followed the same six-lesson unit of gymnastics with identical lesson objectives . The experimental class teacher included the additional objective of increasing MVPA during each lesson . MVPA  was assessed in all six lessons using heart rate ( HR ) monitoring and systematic observation . After each lesson , students ' intrinsic motivation and perceived competence were assessed , and the teachers evaluated whether they had met planned objectives . The experimental group engaged in more  MVPA  [ F(1 , 21 ) = 8.49 , P = 0.008 ( HR ) , t8 = -2.35 , P = 0.048 ( observation ) ] than the control group and also had most opportunities for skill practice ( t8 = -2.81 , P = 0.023 ) . Intrinsic motivation and perceived competence levels were similar between the groups for each lesson , and teachers reported that lesson objectives were satisfactorily achieved . This intervention succeeded in increasing MVPA without compromising intrinsic motivation , perceived competence or planned lesson objectives Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more PURPOSE This study was conducted to determine the effect of physical education class enrollment and physical activity on academic achievement in middle school children . METHODS Participants were 214 sixth- grade students r and omly assigned to physical education during either first or second semesters .  Moderate and vigorous physical activity ( MVPA ) ( number of 30-min time blocks ) outside of school was assessed using the 3-d physical activity recall ( 3DPAR ) . The 3DPAR time blocks were converted to ordinal data with scores of 1 ( no activity ) , 2 ( some activity ) , or 3 ( activity meeting Healthy People 2010 guidelines ) . Academic achievement was assessed using grade s from four core academic classes and st and ardized test scores ( Terra Nova percentiles ) . RESULTS Grade s were similar regardless of whether students were enrolled in physical education during first or second semesters . Physical education classes averaged only 19 min of MVPA . Students who either performed some or met Healthy People 2010 guidelines for vigorous activity had significantly higher grade s ( P < 0.05 ) than students who performed no vigorous activity in both semesters . Moderate physical activity did not affect grade s. St and ardized test scores were not significantly related to physical education class enrollment or physical activity levels . CONCLUSION Although academic achievement was not significantly related to physical education enrollment , higher grade s were associated with vigorous physical activity , particularly activity meeting recommended Healthy People 2010 levels BACKGROUND Although adolescence is a time when physical activity levels decline , few interventions have targeted high school-aged girls in the school setting . OBJECTIVE To evaluate the effects of a life skills-oriented physical activity intervention for increasing overall physical activity in high school-aged girls . DESIGN R and omized controlled trial . SETTING Baltimore magnet high school . PARTICIPANTS A total of 221 ninth- grade girls , 83.0 % of whom were African American . Intervention Participants were r and omized to an 8-month physical intervention conducted in physical education class or to a st and ard physical education class ( control ) . MAIN OUTCOME MEASURES Self-reported estimated daily energy expenditure ( physical activity ) , self-reported sedentary activities ( television viewing and computer or Internet use ) , cardiorespiratory fitness , and selected cardiovascular disease risk factors . RESULTS Intervention classes spent 46.9 % of physical education class time in moderate to vigorous activity compared with 30.5 % of time for control classes ( P<.001 ) . There were no significant between-treatment group differences for mean daily energy expenditure ( P = .93 ) , moderate-intensity energy expenditure ( P = .77 ) , or hard to very hard energy expenditure ( P = .69 ) . The proportion of participants who spent 3 or more hours viewing television during school days declined from 22.3 % to 17.0 % in the intervention group , but remained at 26.7 % for the control group ( P = .03 ) . Both groups improved their cardiorespiratory fitness ( P<.001 ) . CONCLUSION A life skills-oriented physical education curriculum may need to be combined with other approaches to increase the magnitude of effects on physical activity behavior in predominantly African American high school-aged girls Background Physical activity interventions targeting children and adolescents ( ≤18 years ) often focus on complex intra- and inter-personal behavioral constructs , social-ecological frameworks , or some combination of both . Recently published meta-analytical review s and large-scale r and omized controlled trials have demonstrated that these intervention approaches have largely produced minimal or no improvements in young people ’s physical activity levels . Discussion In this paper , we propose that the main reason for previous studies ’ limited effects is that fundamental mechanisms that lead to change in youth physical activity have often been overlooked or misunderstood . Evidence from observational and experimental studies is presented to support the development of a new theory positing that the primary mechanisms of change in many youth physical activity interventions are approaches that fall into one of the following three categories : ( a ) the expansion of opportunities for  youth  to be active by the inclusion of a new occasion to be active , ( b ) the extension of an existing physical activity opportunity by increasing the amount of time allocated for that opportunity , and /or ( c ) the enhancement of existing physical activity opportunities through strategies design ed to increase physical activity above routine practice . Their application and considerations for intervention design and interpretation are presented . Summary The utility of these mechanisms , referred to as the Theory of Exp and ed , Extended , and Enhanced Opportunities ( TEO ) , is demonstrated in their parsimony , logical appeal , support with empirical evidence , and the direct and immediate application to numerous setting s and context s. The TEO offers a new way to underst and youth physical activity behaviors and provides a common taxonomy by which interventionists can identify appropriate targets for interventions across different setting s and context s. We believe the formalization of the TEO concepts will propel them to the forefront in the design of future intervention studies and through their use , lead to a greater impact on youth activity behaviors than what has been demonstrated in previous studies Background Recent data show that only 15 % of Australian adolescents participate in adequate amounts of physical activity ( PA ) and those students from Asian and Middle-Eastern background s in Grade s 6–12 are significantly less active than their English-speaking background peers . Schools have recently been recognised as the most widely used and cost-effective setting for promoting PA among youth and one domain within schools where PA can occur regularly for all youth , regardless of cultural background or socio-economic status , is during physical education ( PE ) . Methods This study describes changes in physical activity ( PA ) , lesson context and teacher interaction in physical education over the first two years in culturally and linguistically diverse secondary schools . Grade 7 PE classes in six schools were r and omly observed using systematic direct observation ( n = 81 ) and then followed up over the same period ( n = 51 ) twelve months later . Results There was no significant decline in moderate-to-vigorous physical activity ( MVPA ) during PE ( MD = −4.8 % ; p = .777 ) , but a significant decline and medium negative effect in time spent in vigorous physical activity ( VPA ) ( MD = −7.9 % ; p = .009 ) during PE was observed . Significant declines and large negative effects over time in percentage of PE time spent in management ( MD = −8.8 % ; p < .001 ) and the number of observations where teachers promoted  PA ( MD = −20.7 % ; p < .001 ) . Conclusions The decline of VPA and teacher promotion of PA in culturally and linguistically diverse schools is of concern . Given the declines in VPA and the increases in time spent in game play , further research is needed to ascertain whether PE instruction could be improved by focussing on skill instruction and fitness in a games-based PE instruction model . Further research for increasing teacher promotion of PA during PE is needed The Central Texas Coordinated Approach To Child Health ( CATCH ) Middle School Project is a 3.5-year school-based project aim ed at promoting physical activity ( PA ) , healthy eating , and obesity prevention among public middle school students in Texas . This article describes the CATCH intervention model and presents baseline findings from spring 2009 . CATCH comprises six core components : CATCH Team , CATCH PE , CATCH Classroom , CATCH Eat Smart Cafeteria , CATCH Family , and CATCH Social Marketing . A group r and omized serial cross-sectional design is being employed to test the effect of three program support conditions ( n = 10 schools each ) on energy-balance behaviors : Basic ( training and curriculum only ) , Basic Plus ( training and curriculum plus CATCH facilitator support ) , and Basic Plus Social Marketing ( all inputs plus social marketing component ) . The study sample is composed of a cross-sectional sample of eighth- grade students ( primary outcome evaluation sample ) and sixth- and seventh- grade students ( PE process evaluation sample ) who are selected and measured each year . At baseline , 37.9 % of eight- grade students ( n = 2,841 ; 13.9 years ) were  overweight/obese  and 19.2 % were obese . Eighth- grade students reported , on average , consuming sugar-sweetened beverages more than two times on the previous day and fruits and vegetables roughly three times on the previous day ; only two of five school districts surpassed the recommended 50 % cut-point for class time spent in moderate- and -vigorous PA as measured in classes of sixth- and seventh- grade students . Additional behavioral findings are reported . Body mass index and behaviors were comparable across conditions . Baseline findings underscore the need to promote student energy-balance behaviors This study was design ed to explore the effects of a health-related physical fitness physical education model on students ' physical activity , perceived competence , and enjoyment .  61 students ( 25 boys , 36 girls ; M age = 12.6 yr . , SD = 0.6 ) were assigned to two groups ( health-related physical fitness physical education group , and traditional physical education group ) , and 
    Output:
    
Findings differed according to the method of MVPA assessment .