Key messages
School-based interventions may improve physical fitness but may have little to no impact on body mass index (which is used to assess whether body weight is in a healthy range), although we do not have confidence in the evidence.
Very few studies have reported on any potential harmful effects.
Careful consideration is needed about the type of school-based physical activity programme to be implemented, and future studies should seek to identify the best types of physical activity interventions for school settings.
Why is it important to promote physical activity in children?
It is estimated that as many as 5.3 million deaths worldwide are caused by not getting enough exercise (physical inactivity), and this is a big risk factor leading to most long-lasting diseases and cancers. This is a topic of concern, particularly because it is known that physical activity patterns in childhood can lead to similar patterns in adulthood. Programmes that encourage children to exercise while at school are thought to be a way to increase activity levels of all children, regardless of other factors such as parent behaviours and social or financial factors of a child’s early lifetime.
What did we find?
We found 89 studies that looked at the effects of programmes in schools that focused on increasing physical activity, which included 66,752 children and adolescents (between the ages of 6 and 18) from around the world. The length of programme time varied from 12 weeks to 6 years. No two school-based physical activity programmes used the same combination of intervention parts. How often and how long each part of a programme was run varied a lot across studies.
Across all included studies, only very small changes were noted in the number of students undertaking physical activity or in minutes per day of moderate to vigorous physical activity or sedentary time, although these programmes were found to improve students’ physical fitness. These programmes were found to have little to no impact on measurements used to assess whether body weight is in a healthy range. Not many studies reported on any potential harmful effects, such as injury or psychological harm.
What are the limitations of the evidence?
We have little confidence in the evidence because studies were done in different ways and interventions were delivered and assessed in different ways. Also, people in the studies may have been aware of which interventions they were getting, and this can sometimes affect the outcomes reported. In addition, not all studies provided data about everything we were interested in.
How up-to-date is the evidence?
The evidence is up-to-date to June 2020 (although we did run a new search for studies in February 2021 and found studies that may be included in a future update and are now described in the “Studies awaiting classification” table).
Given the variability of results and the overall small effects, school staff and public health professionals must give the matter considerable thought before implementing school-based physical activity interventions. Given the heterogeneity of effects, the risk of bias, and findings that the magnitude of effect is generally small, results should be interpreted cautiously.
Physical activity among children and adolescents is associated with lower adiposity, improved cardio-metabolic health, and improved fitness. Worldwide, fewer than 30% of children and adolescents meet global physical activity recommendations of at least 60 minutes of moderate to vigorous physical activity per day. Schools may be ideal sites for interventions given that children and adolescents in most parts of the world spend a substantial amount of time in transit to and from school or attending school.
The purpose of this review update is to summarise the evidence on effectiveness of school-based interventions in increasing moderate to vigorous physical activity and improving fitness among children and adolescents 6 to 18 years of age.
Specific objectives are:
• to evaluate the effects of school-based interventions on increasing physical activity and improving fitness among children and adolescents;
• to evaluate the effects of school-based interventions on improving body composition; and
• to determine whether certain combinations or components (or both) of school-based interventions are more effective than others in promoting physical activity and fitness in this target population.
We searched CENTRAL, MEDLINE, Embase, CINAHL, PsycINFO, BIOSIS, SPORTDiscus, and Sociological Abstracts to 1 June 2020, without language restrictions. We screened reference lists of included articles and relevant systematic reviews. We contacted primary authors of studies to ask for additional information.
Eligible interventions were relevant to public health practice (i.e. were not delivered by a clinician), were implemented in the school setting, and aimed to increase physical activity among all school-attending children and adolescents (aged 6 to 18) for at least 12 weeks. The review was limited to randomised controlled trials. For this update, we have added two new criteria: the primary aim of the study was to increase physical activity or fitness, and the study used an objective measure of physical activity or fitness. Primary outcomes included proportion of participants meeting physical activity guidelines and duration of moderate to vigorous physical activity and sedentary time (new to this update). Secondary outcomes included measured body mass index (BMI), physical fitness, health-related quality of life (new to this update), and adverse events (new to this update). Television viewing time, blood cholesterol, and blood pressure have been removed from this update.
Two independent review authors used standardised forms to assess each study for relevance, to extract data, and to assess risk of bias. When discrepancies existed, discussion occurred until consensus was reached. Certainty of evidence was assessed according to GRADE. A random-effects meta-analysis based on the inverse variance method was conducted with participants stratified by age (children versus adolescents) when sufficient data were reported. Subgroup analyses explored effects by intervention type.
Based on the three new inclusion criteria, we excluded 16 of the 44 studies included in the previous version of this review. We screened an additional 9968 titles (search October 2011 to June 2020), of which 978 unique studies were potentially relevant and 61 met all criteria for this update. We included a total of 89 studies representing complete data for 66,752 study participants. Most studies included children only (n = 56), followed by adolescents only (n = 22), and both (n = 10); one study did not report student age. Multi-component interventions were most common (n = 40), followed by schooltime physical activity (n = 19), enhanced physical education (n = 15), and before and after school programmes (n = 14); one study explored both enhanced physical education and an after school programme. Lack of blinding of participants, personnel, and outcome assessors and loss to follow-up were the most common sources of bias.
Results show that school-based physical activity interventions probably result in little to no increase in time engaged in moderate to vigorous physical activity (mean difference (MD) 0.73 minutes/d, 95% confidence interval (CI) 0.16 to 1.30; 33 studies; moderate-certainty evidence) and may lead to little to no decrease in sedentary time (MD -3.78 minutes/d, 95% CI -7.80 to 0.24; 16 studies; low-certainty evidence). School-based physical activity interventions may improve physical fitness reported as maximal oxygen uptake (VO₂max) (MD 1.19 mL/kg/min, 95% CI 0.57 to 1.82; 13 studies; low-certainty evidence). School-based physical activity interventions may result in a very small decrease in BMI z-scores (MD -0.06, 95% CI -0.09 to -0.02; 21 studies; low-certainty evidence) and may not impact BMI expressed as kg/m² (MD -0.07, 95% CI -0.15 to 0.01; 50 studies; low-certainty evidence). We are very uncertain whether school-based physical activity interventions impact health-related quality of life or adverse events.