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Effect of school-based interventions on physical activity and fitness in children and adolescents: a review of reviews and systematic update
  1. S Kriemler1,2,
  2. U Meyer1,
  3. E Martin2,
  4. E M F van Sluijs3,
  5. L B Andersen4,5,
  6. B W Martin2
  1. 1Swiss Tropical and Public Health Institute, University of Basel, Basel, Switzerland
  2. 2Institute of Social and Preventive Medicine, University of Zürich, Zürich, Switzerland
  3. 3Medical Research Council Epidemiology Unit & UKCRC Centre of Excellence in Diet and Activity Research, University of Cambridge, Cambridge, UK
  4. 4Center for Research in Childhood Health, Department of Exercise Epidemiology, University of Southern Denmark, Odense, Denmark
  5. 5Department of Sports Medicine, Norwegian School of Sports Sciences, Oslo, Norway
  1. Correspondence to S Kriemler, Swiss Tropical and Public Health Institute, University of Basel, Socinstr 59, 4002 Basel, Switzerland; susi.kriemler{at}unibas.ch

Abstract

Background School-based interventions are thought to be the most universally applicable and effective way to counteract low physical activity (PA) and fitness although there is controversy about the optimal strategy to intervene.

Objectives The objective of this review was to summarise recent reviews that aimed to increase PA or fitness in youth and carry out a systematic review of new intervention studies.

Methods Relevant systematic reviews and original controlled and randomised controlled school-based trials with a PA or fitness outcome measure, a duration of ≥12 weeks, a sufficient quality and involvement of a healthy population aged 6–18 years that were published from 2007 to 2010 were included.

Results In these reviews, 47–65% of trials were found to be effective. The effect was mostly seen in school-related PA while effects outside school were often not observed or assessed.

Conclusions The school-based application of multicomponent intervention strategies was the most consistent, promising strategy, while controversy existed regarding the effectiveness of family involvement, focus on healthy populations at increased risk or duration and intensity of the intervention. All 20 trials in the review update showed a positive effect on in-school, out-of-school or overall PA, and 6 of 11 studies showed an increase in fitness. Taking into consideration both assessment quality and public health relevance, multicomponent approaches in children including family components showed the highest level of evidence for increasing overall PA. This review confirms the public health potential of high quality, school-based PA interventions for increasing PA and possibly fitness in healthy youth.

https://doi.org/10.1136/bjsports-2011-090186

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    Introduction

    Physical inactivity and low fitness in children and adolescents are raising health burdens worldwide. Physical inactivity in adults has been established as one of the leading established risk factors for mortality1 and burden of disease.2 Moreover, high fitness has been shown to prolong life and even seems to be able to counterbalance adiposity-related mortality.1 The fact that these factors also track into adulthood3 emphasises the necessity to evaluate and find effective strategies for increasing physical activity (PA) and fitness in youth. School is the place where almost all children and adolescents spend most of their days and family-based interventions have been shown to be of limited effectiveness.4 5 Therefore, a focus on the globally available school system seems justified.

    As well-performed and relatively recent systematic reviews were available, we decided to summarise existing knowledge from these reviews and focus on the new literature of school-based interventions not included in the earlier reviews. We have used compatible search strategies and have not included articles published during the periods studied in the earlier reviews, but some studies may have been included in several reviews.

    The objective of this review was therefore to: (1) summarise recent reviews of studies that aimed to increase PA or fitness in children and adolescents; (2) define, based on these reviews, potentially relevant factors for a positive outcome; (3) carry out a systematic review of new intervention studies and prospectively verify the predefined factors.

    Methods

    The base of this review was the collection of recent systematic reviews published after 2006 that summarised the evidence on PA promotion in children and adolescents and to update these reviews by searching original controlled and randomised controlled school-based trials published afterwards. The reviews were analysed in detail by one researcher (SK) and discussed with the coauthors.

    Literature search and quality control

    For our own systematic review, we used a combination of the search strategy used by others5 6 and applied it to Pubmed, Medline, Embase, Psycinfo, Sportdiscus and Embase using a time frame from January 2007 to December 2010 (online supplementary table 1). Inclusion criteria were: (1) controlled trials (CTs) or randomised controlled trials (RCTs) of interventions that aimed to increase PA or fitness, (2) target populations including school-aged children from 6 to 18 years of age (corresponding to the mandatory school age), (3) PA or fitness measured as an outcome at baseline and at least one follow-up, (4) a duration of the intervention of at least 3 months, (5) intervention delivered at school, (6) control group not receiving a PA intervention and (7) statistical analyses of the PA/fitness outcome reported. Studies in children with a specific disease or studies applying structured exercise programmes for obese children were excluded. Likewise, we did not include trials with the main goal of decreasing inactivity.

    Two reviewers (SK, MU) each checked half of the titles and abstracts obtained from the searches. After exclusion of non-relevant studies, the full text of each remaining paper was read by two researchers (MU and SK or EM) who independently scored them. The methodological quality of the studies was then assessed using a predefined previously used quality assessment tool focusing mainly on internal validity (online supplementary table 3).5 Any disagreement was solved by discussion and studies with a weak methodology, that is, with a score below 5 of 10, were excluded.

    Data extraction and evaluation

    An overview of the studies included was established. Thereafter, a checklist with the relevant trial characteristics was constructed to allow systematic data extraction. These factors included the age group (children vs adolescents), duration of the trials (interventions of 1 year or less vs longer trials), focus of the trials (solely on the school setting vs including also family or community components), implementation by classroom teachers or physical education (PE) specialists, mandatory or voluntary nature of the intervention and method of outcome assessment (accelerometers, pedometers or observation vs questionnaires; Vo2max test vs field tests). Children were defined as the age group up to 12 years, while adolescents were 13 years old or older. A programme was defined as mandatory if the intervention was an integral part of the school curriculum in which neither teachers nor children had the free choice of participation or withdrawal, and if there was a report of compliance or the intervention was monitored. This rating was carried out by two independent researchers prior to the systematic reporting of study results. In case of disagreement consensus was reached by discussion.

    Results

    Summary and synthesis of recent reviews with focus on the school setting

    Table 1 provides an overview of the four most recent and comprehensive systematic reviews covering PA promotion in schools.4,–,8 The reviews included CT or (cluster)-RCTs with the goal of PA promotion in youth reporting a baseline and at least one follow-up measure of PA and/or fitness. Between 75%4 and 100%6of the studies included focused on the school system. While the upper range of age included was generally 18–19 years, the lower range of age varied from no limit5 to 4 years,4 6 years6 or 10 years.7 A description of the reviews and their conclusions is provided below.

    View this table:
    Table 1

    Overview of systematic reviews of school-based PA or lifestyle interventions to increase PA or fitness in children and adolescents

    Dobbins et al6reviewed the available evidence of school-based PA promotion including trials up to June 2007. After a rigorous quality control of the potentially eligible trials based on Cochrane recommendations, they reported results of 26 studies. They reported positive impact on duration of PA (mostly for PA during school time) and on aerobic fitness measured by Vo2max, but there was no evidence that school-based trials also affected out-of-school PA positively. Although the authors were positive about the beneficial effects in general, this evidence was mostly based on self-reports. The authors discussed several limitations of the included studies such as the low number of trials reporting out-of-school PA (n=7) despite the fact that the primary goal of most trials was to promote overall PA, the lack of long-term follow-up and the measurement of PA mostly by self-report, which may have attenuated the results due to the inability to accurately report PA by children.9 They further remarked that the most notable difference regarding effects on out-of-school PA was the use of PE specialists to deliver the intervention. For PA in school, successful trials tended to intervene for a longer period and applied multicomponent approaches. All these studies were conducted in children.

    De Meester et al7 included trials in European teenagers that were published from 1995 to May 2008 and identified 20 relevant studies. They found that school-based interventions lead to short-term improvements in PA levels, but effects were limited to school-related PA with no conclusive transfer to out-of-school PA. In a second article integrating the analyses of effect sizes8 they concluded, in contrast to the original review, that a multicomponent approach including environmental components and a focus on PA only rather than aiming to change several health behaviours was most effective. PA improvements were reported to be of short duration, as in all three studies including longer term follow-up increases were not maintained. The authors also discussed the absence of school-based PA increases to out-of-school PA increases. Their original suggestion of an additional involvement of families was supported by three favourable trials combining the school and family setting. However, based on the effect size calculations it was later considered premature.8

    Salmon et al4 reviewed the literature from 1985 to June 2006 and summarised the findings of 76 studies, with 57 (75%) of them carried out in the school setting. Half of the studies were effective at increasing PA (not further specified). The authors observed that 16 (64%) of 25 studies using objective PA measures reported positive effects on PA compared with 25 (38%) of 66 studies using questionnaires. They felt that multicomponent interventions focusing on PE that implemented activity breaks or included family strategies were most successful among children, but the situation was inconclusive in adolescents. In many trials, overall PA was not measured, leaving the debate open whether successful increases in PA during school would be sustained during out-of-school or rather compensated by a respective decrease as suggested10 11 by others. Many of the studies included in this review were not considered in the review by Dobbins et al6 because of weaknesses in their methodology, although this was recognised.

    Van Sluijs et al5 summarised all interventions with a PA promotion in youth up to December 2006. Fifty-seven studies were identified, with 47 involving the school system and about half of them of high quality. As in the other reviews presented above, a meta-analysis was not performed, because of the methodological heterogeneity of the studies. Although all studies that fulfilled the inclusion criteria were included, the level of evidence was drawn on the basis of consistency of results of studies with the highest available level of quality. Strong evidence was found for the effectiveness of multicomponent interventions and for trials including both school and family or community components in adolescents, while there was no conclusive finding for the best strategy in children. Interventions seemed to be more effective in adolescents than in children. Based on their findings, the authors questioned the usefulness of interventions targeting ethnic minority populations or girls only, or approaches using isolated educational approaches. They also mentioned important limitations of many studies caused by the absent description of attendance, of implementation or of quality assurance in the interventions. The total lack of cross-cultural evaluation of the studies also made it impossible to generalise findings from different parts of the world.

    In summary, the existing reviews of trials promoting PA in schools agreed upon their positive impact but have not supplied a clear picture of effective strategies to increase PA and/or fitness in youth. Their conclusions concerning the effects of specific intervention types in different age groups varied. Methodological limitations in existing studies were cited including the lack of valid PA measures, lack of data on overall PA and compliance, and the lack of studies with long-term follow-up or clear implementation strategies. All reviews requested that more trials of adequate quality should be performed.

    New literature since January 2007

    Figure 1 presents a flowchart of the literature search. We identified 20 relevant trials (11 RCTs and 9 CTs) (online supplementary table 2)12,–,33 of sufficient quality (see online supplementary table 3 for the rating system and the results of the methodological quality assessment) published between January 2007 and December 2010. Sixteen of 20 trials reported effects on a PA outcome, 11 of 20 reported on a fitness-related outcome and 6 of 20 also assessed motor skills. A list of excluded studies, based on full text reviews, is provided in online supplementary table 4.

    Figure 1
    Figure 1

    Flowchart of study selection.

    Three trials were performed in the USA, two in Canada, 12 in Europe and one each in Australia, Brazil and Iran. The study size at baseline ranged from 132 to 2848 and the duration of the intervention from 6 months to 4 years, including seven trials with a duration of more than a year.12 14 18 23 28 29 32Only three trials reported follow-ups of 6–12 months after the end of the intervention.15 24 25 Fourteen trials included children until 12 years of age, four studies were done in adolescents and two trials included both age ranges. Most studies focused on a general population of school children, two studies only included girls27 30 and three focused on children from low socioeconomic backgrounds.21 24 25 About half of the programmes were mandatory rather than voluntary, also half of them were multicomponent and 60% included family or community components. The intervention was applied by PE experts in five studies, while in nine studies classroom teachers were responsible for the implementation and in three studies a combination was used. Among the 16 studies with a PA outcome, 6 trials solely used questionnaires to assess PA13 16 21 26 28 30 and 10 used accelerometers or pedometers in the whole sample15 17 20 22 24 25 or a subsample,12 17 19 32 including 6 that used a combination of PA assessments. Common methodological limitations of the included studies were missing information on the use of intention-to-treat analyses, on blinding procedures or on randomisation procedures and compliance.

    Contentwise, each single study was different and none of the programmes used the same content of intervention. Overall, four programmes focused solely on education, four applied only curricular changes, one only changed the environment while the remaining trials used any combination of approaches with educational, curricular or environmental adaptations. About half of the programmes complemented PE lessons and/or added PA breaks, supported active play during recess, lunchtime or after school. This included, for example, adding additional PE lessons, provision of equipment, more time for breaks, PA homework or special events during weekends. In addition, most programmes added some sort of education as extra lessons during school or as an integrated part of the usual curriculum. Two-thirds of all trials integrated family components ranging from simple written advice to audiovisual education or active participation in workshops with or without the children or adolescents. Main results are described in table 2.

    View this table:
    Table 2

    Overview of the studies included in the updated review, classified by effectiveness on PA, fitness and motor skills

    Effect on PA

    The overall picture shows that every single study with a PA outcome (n=16) reported a significant intervention effect in at least one domain of PA, in-school, out-of-school or overall. We defined a hierarchy of PA findings including assessment quality (ie, objective vs subjective means of PA measurement, RCT vs CT) and public health relevance (ie, overall vs in-school vs out-of-school PA) by using one key PA measure per study that provided the strongest evidence of an intervention effect. Five studies were effective at increasing total PA assessed by accelerometers or pedometers,15 17 20 22 25 but two of them showed significant effects only in a subgroup.15 22 By the use of questionnaires, total PA was increased in four studies14 16 27 30 (one in a subgroup14) while one did not show effects.19 In-school PA was increased in two studies,24 31 both using objective means of assessing PA. Out-of-school PA was only assessed by subjective means, but all these four studies12 13 21 28 showed significant positive effects on PA in favour of the intervention. Among the three studies documenting a longer follow-up (6–12 months), all reported maintained effects in at least one measure of PA.15 25 34 Two RCTs with an intervention duration of one school year attained the highest hierarchy level of evidence with significant increases of objectively measured overall PA in the whole study population of children. One applied daily PE lessons with additional PA breaks and PA homework,20 the other focused on providing weekly sessions of behavioural modification (regarding PA and sedentary behaviour), improvement of fundamental motor skills or a combination of both.25 Both RCTs were integrated as part of the school curriculum, used PE specialists and included family support.

    Effect on aerobic fitness and motor skills

    Aerobic fitness was assessed in 11 studies, of which 3 used spiroergometry (Vo2max)27 33 35 and the remaining used field tests such as the shuttle run or a 6-minute run. Six studies20 22 23 27 29 33 showed significant intervention effects, including all studies with Vo2max measurements. They all used PE specialists to implement the weekly programme, which generally consisted of five sessions of at least 45 min. Six studies also assessed motor skills in addition to fitness or PA.14 17 25 29 31 33 Measurements differed considerably, ranging from observational ratings of the form and function of fundamental movement skills like forehead strike, lift and carry or leap14 to different validated test batteries such as the body coordination test (KTK)18 33 or the Eurofit test.29 32 Four of the trials10 13 22 26 showed significant positive intervention effects. Concomitant effects on fitness or PA were inconsistent and heterogeneous. No follow-up assessments for fitness or motor skills were reported.

    Discussion

    The school setting has long been defined as the ideal setting for PA promotion interventions. As young people spend the majority of their waking hours in the school setting, it is possible to globally reach the population of interest without having to stigmatise or discriminate and without being primarily dependent on families. Recent reviews generally showed that school-based PA promotion was effective at increasing PA during school, while the critical transfer to a parallel increase in out-of-school or overall PA was less clear. The reviews agreed that multicomponent interventions combining educational, curricular and environmental elements seem to be more effective than isolated education5 or curricular changes4, but opinions differed on whether this was the case for children and adolescents. In some reviews, the focus on change of multiple health behaviours instead of focusing only on PA was considered as a stumbling block for success.6 7 The involvement of families within school-based interventions was well supported by most,4,–,6 but not all reviews.7 8 While van Sluijs et al5 stated that studies in adolescents tended to be more successful than in children possibly because of more potential for change and/or a higher quality of the studies, the other reviews were unable to draw the same conclusion, possibly limited by the small numbers of trials in the adolescent age range. In general, it was highlighted that many studies were of questionable methodology, that is, they assessed only school-related PA and used only questionnaires or permitted only conclusions on short-term follow-up. There was questionable generalisability because of the lack of trans-cultural studies.

    The updated literature review identified 20 studies that fulfilled the inclusion and quality criteria and revealed a highly consistent picture with all included studies documenting significant effects on at least one measure of PA and 6 out of 11 trials reporting a significant positive effect on fitness. These findings document stronger evidence than ever that school-based PA interventions are able to increase PA and possibly fitness in healthy children and adolescents. The intervention effects were consistently positive for PA in school, out-of-school PA and even more importantly in 9 out of 10 studies for overall PA. In contrast to most previous reviews, only trials with adequate methodology, a preassessment and postassessment of PA or fitness and a minimal duration of 3 months were included. The minimal duration was chosen to ascertain training effects36 and at least some sustainability of behavioural change as suggested,6 thereby increasing the strength of evidence of these findings. Of note, the inclusion of four studies excluded only based on short duration37,–,40 would not have changed the conclusions drawn here.

    Publication bias in the sense of under-reporting of studies with negative effects might have influenced the overall picture, particularly given the high number of effective studies. However, given the considerable effort that goes into carrying out a proper outcome assessment, it can be assumed that researchers willing to make this effort will also strive to publish their findings even if they are negative. Therefore, one might consider not generalising the conclusions of this review to low intensity and low effort PA promotion interventions in schools.

    The fact that 20 trials were eligible over a 4-year period (compared with 26 trials over 50 years in the Cochrane review6) shows important progress in quality of the published studies. Seventy-five per cent of all trials assessing a PA outcome reported on overall PA; in 60% of all studies the PA outcome was measured by objective means. The predominance of positive intervention effects on PA was no longer limited to school-based PA, but extended to out-of-school and overall PA. From a public health perspective, this is a very important finding.

    In the current review compared with the previous reviews, the proportion of European studies was considerably higher. The methodological quality of the included studies has improved considerably, with more overall and objective assessments of PA and with more adequate statistical analyses (ie, power analyses, cluster adjustment). When looking at the trials with the highest combined hierarchy level of quality and public health relevance (ie, RCTs that assessed overall PA objectively and found significant effects in the whole study population), they included children, intervened over one school year by multicomponent approaches including PE, behavioural modification lessons or a combination. The programmes were integrated into the regular school curriculum and taught by PE experts, and tried to involve families using written information. Although one has to be cautious to draw conclusions based on two trials, a multicomponent mandatory programme with the involvement of specialists and supported by the families seems to be effective in increasing overall PA in children. Interestingly, similar conclusions have been drawn for lifestyle interventions in children to reduce obesity.41

    These findings confirm previous recommendations to use multicomponent approaches in children to broaden the reach of the population of interest,4 5 and to include families as important mediators for PA outside the school4 and for positive attitudes towards PA in general.42 Whether the involvement of family components in school-based interventions for adolescents proves beneficial remains open for debate. While van Sluijs et al5 described strong evidence based on positive findings in two out of three high quality RCTs, the findings in the review by De Meester et al7 were inconclusive and effect sizes in the three effective studies were at most moderate.8It is possible that the influence of the family on health behaviour becomes less important in debonding adolescents who are trying to become autonomous.

    There was no difference in the effect of interventions on PA regardless of whether the study used objective or self-report measures of PA, which is in contrast to the findings of previous reviews.4 5 However, several studies used objective means of PA assessment only in a subpopulation,17 19 31 43 which may have induced a selection bias, and some even reported discordant findings when objective and subjective means were both applied.19 Nevertheless, there is no doubt that objective means of assessing PA in the whole study population should be the goal in the future.44 Methodological limitations such as the absence of proper description of the randomisation procedures to judge representativeness of the population, of documentation of compliance of those applying or receiving the intervention and, finally, of long-term follow-ups were still present.

    Trials assessing aerobic fitness by Vo2max were consistently effective at increasing it, while only half of the trials using field tests showed positive effects. Additional factors differentiating effective from ineffective trials were a duration of the intervention of less than 1 year, a mandatory compared with a voluntary nature of the intervention, and an intervention in school only rather than extending it to the family or community. Importantly, all these trials used PE specialists to implement the programme, which consisted of daily sessions of at least 45 min. Studies without an effect on fitness were less intensive, less extensive and mostly voluntary in nature. This underlines the importance of an intervention of sufficient quantity and quality. The method of measuring aerobic fitness may also be an important consideration, since field tests may have methodological limitations in precision, motivation and standardisation. The fact that shorter programmes were more effective highlights the risk of losing the interest of teachers and pupils over time. The success of mandatory programmes could be indirect evidence that compliance is one of most critical factors in school-based interventions to raise aerobic fitness as one of the most important health factors in youth.36

    In general, effects of the intervention on PA were stronger than the effects on fitness. This might be because the changes in PA were not sufficient to cause changes in fitness, the measurements were not of sufficient accuracy or there was simply over-reporting.

    Motor skills were not defined as a main outcome in this review, but they were reported as an additional finding in some trials. Four of six studies showed significant intervention effects on motor skills, but concomitant effects on fitness or PA were heterogeneous. Based on this review we cannot draw any conclusion on the relevance of focusing on motor skills to increase PA or fitness, although it may be plausible that children and adolescents with improved motor skills would have the precondition to increase their fitness or PA by their improved competence.45

    There is now good evidence that school-based interventions can increase PA and fitness in youth. Although this is a first step towards improving health and well-being in youth, we are still faced with the much bigger challenge of establishing the sustainability of these interventions and their effects as well as transferring these programmes into real-world settings. The proof of sustainability of effects in these efficacy trials will probably never be done due to the ‘dispersion nature’ of schoolchildren. Some research groups have tried to perform long-term follow-ups but evidence remains brittle because of the tiny percentage of the original study populations that could be reached.46,–,48 Yet, effectiveness trials in larger populations and different settings may shed light on the capacity of large-scale and long-term health effects of PA promotion in youth as nicely shown in malaria prevention programmes.49 One programme that may be an example in this direction is the Action Schools! BC initiative,50 51 which was started in 2004 including 275 schools and 25 740 children and reaching 550 000 children 6 years later. This implementation was supported by the provincial government mandating 30 min of daily PA in schools. In order to find the best effectiveness for PA interventions in youth, research efforts should include studying mediation of the intervention effect52 53 and implementation issues,43 54 which should enable us to successfully reach large populations. Further research also needs to consider the generalisability of the results as most of the studies included in the updated review originated from Europe. Now that we are more confident that school-based PA interventions have the potential to change young people's PA behaviour, at least in the short term, we need to focus on programmes that obtain the highest effect sizes,8 but also study the cost-effectiveness in real-world trials ideally with long-term follow-ups. Only then can we be more confident that PA changes in youth can be sustained and translated into better health in later life, as previously suggested.36 48 55,–,57

    Conclusion

    This review shows strong evidence for the positive effect of school-based interventions on PA in children and adolescents. These conclusions are based on four systematic reviews published after 2006 of studies focusing on PA promotion in school and other settings and on a new systematic review of trials published between January 2007 and December 2010. Our review of the more recent publications is the first to show that PA promotion in the school setting leads to an increase in school-based PA and is associated with an increase in out-of-school, and even more importantly, in overall PA. There is some evidence that school-based interventions can have positive effects on aerobic fitness, although this evidence is weak. Since efficacy of school-based PA promotion is globally evident, the time is ripe to look at long-term effects and figure out effective implementation strategies.

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