School-Based Intervention Programs for Preventing Obesity and Promoting Physical Activity and Fitness: A Systematic Review

With the significant decrease in physical activity rates, the importance of intervention programs in the schools, where children spend a significant part of the day, has become indisputable. The purpose of this review is to systematically examine the possibility of school-based interventions on promoting physical activity and physical fitness as well as preventing obesity. A systematic approach adopting PRISMA statement was implemented in this study. Three different databases (2010–2019) were screened and primary and secondary school-based intervention programs measuring at least one variable of obesity, physical activity, or physical fitness were included. The risk of bias was assessed using the validated quality assessment tool for quantitative studies. Among 395 potentially related studies, 19 studies were found to meet the eligibility criteria. A general look at the studies examined reveals that among the outcomes, of which most (18/19) were examined, a significant improvement was provided in at least one of them. When the program details are examined, it can be said that the success rate of the physical activity-oriented programs is higher in all variables. School-based interventions can have important potential for obesity prevention and promotion of physical activity and fitness if they focus more on the content, quality, duration and priority of the physical activity.


Introduction
Physical activity (PA) is one of the most effective ways of preventing cardiovascular and mental illnesses and improving physical fitness (PF). Regular PA reduces the risk factors of many diseases such as high blood pressure, diabetes and obesity [1]. On the other hand, inactivity may cause obesity and a low level of cardiovascular fitness and increase the risk of high blood pressure and cholesterol with children. This situation also may lead to the development of chronic diseases such as high blood pressure and diabetes during adulthood [2]. In the systematic study of Janssen and Leblanc [3] where the relationship between PA, PF, and health of school-age children and adolescents were examined, it was found that PA contributed significantly to health, especially in high-risk youth, and that PA should be continued at least moderately to maintain health benefits and that vigorous activities provided more benefits. In another systematic study examining the interventions to increase moderate-to-vigorous (MVPA) PA in physical education classes, it was concluded that the intervention could increase MVPA levels throughout the course and provide significant benefits to public health [4].
To achieve health benefits, it is recommended to exercise with MVPA intensity for five days a week or more for at least 30 min, or with vigorous intensity for at least 20 min for 3 days [5]. The World Health Organization (WHO) [6] recommends MVPA for children and adolescents for at least 60 min per day. Despite the importance of regular PA, PA levels have started to decrease together with the new tools such as smartphones, computers, tablets, video games and social media, that have come into our lives in relation to technology [1]. PF of children has also declined with low levels of PA [7]. High levels of PF in children and adolescents are linked to physical and mental health [8]. At this point, the role of schools, where children and adolescents spend a significant portion of their days, in providing PA opportunities has reached an even more critical point. Despite this critical situation, the scope, quantity and quality of physical education courses, as well as the participation rates in extracurricular physical activities are not at the desired levels and differ significantly from school to school [9][10][11]. Schools are easy and provide accessible settings to promote engagement in PA because it is related to the objectives of the physical education curriculum. Children can learn the knowledge, skills and attitudes necessary for lifelong PA habits in schools. WHO [6] maintained that "all children and young people should be physically active with the support of schools or public institutions through games, sports, recreation, physical education and planned physical activities" and underlined the mission of schools regarding PA. School-based PA interventions include various categories such as physical education curriculum, classroom activity breaks, active commuting to school, modified playgrounds and comprehensive multi-component approaches. Along with learning in psychomotor, cognitive and affective domains, PA and PF levels will be promoted and obesity will be prevented over time. In this context, the priority is that children have meaningful learning experiences during their school years. Considering the seriousness of problems, which may occur related to inactivity in children, increasing school-based PA options of children and ensuring that children spend time with PA at schools should be considered a vital task.
Although PA programs in schools are one of the primary sources for promoting PA and FP, children are not active enough and their obesity/overweight levels have reached alarming levels [12][13][14][15]. A sedentary lifestyle and changing dietary habits have significantly increased obesity among children and adolescents [16]. Overweight and obesity are operationally defined as "abnormal or excessive fat accumulations that negatively affect health" [17]. WHO accepts childhood obesity as one of the most important global problems of the 21st century [18]. Overweight or obesity is a very complex phenomenon with many different causes. Although it is widely accepted that the increase in obesity stamps from the imbalance between energy intake and expenditure, it is known that there are many other genetic, environmental and behavioral reasons. The ecological model, as described by Davison et al., suggests that child risk factors for obesity include dietary intake, PA, and sedentary behavior [19]. In addition, environmental and socio-cultural factors such as family characteristics and parents' lifestyle, school policies, and screen culture affect eating and activity behaviors [20]. Therefore, school-based intervention programs to prevent obesity should be designed and diversified in a comprehensive and multicomponent way. Physical inactivity is one of the most important factors in the emergence of obesity [21,22]. Traditional interventions for overweight or obesity include training in healthy nutrition and changing lifestyles by increasing PA. In this context, interventions based on increasing PA are often considered to be the most effective method, not only because they help in weight control but also because of health benefits such as the strengthening of bones and muscles, better sleep, improving mental health and reducing the risk of cardiovascular disease [3,23]. In a longitudinal study performed on more than 6000 children at the age of 7 years doing regular PA, it was concluded that performing PA was associated with the body fat percentage of children at the age of 11 years [24]. Again, researches conducted on children aged between 4 and 18 show that being engaged in regular PA has basic health benefits such as the increasing of bone density, good blood pressure and the improving of metabolic or cardiopulmonary health [3,25]. Apart from these, the benefits of PA can be stated as increased attention span, healthy functioning of cognitive processes, mental health and a general state of being healthy [26,27]. Regardless of the intensity, PA is associated with better health, motor skills and positive cognitive outcomes [28].
School-based PA is a necessary process that requires the structuring of all the time spent in the school, beginning with the planning of the child starting the day actively as s/he comes to school. In order to increase the participation of children in PA in schools and to prevent obesity effectively, it is necessary to increase the active time in physical education courses, to diversify the content of the course, to reevaluate the teacher qualifications and the number of students, to examine the effectiveness of programs for recess, in-school activity, extracurricular activities and school teams. Some systematic studies conducted in this respect have shown that school-based interventions can be effective in preventing obesity and promoting PA [29][30][31]. On the other hand, there are also studies in which variables such as obesity, PA and sedentary behavior are measured and no significant development can be observed [23,32,33]. In a significant part of the studies carried out in the literature, the differentiation of the success of situations in terms of the variables examined necessitates the examination of the studies conducted in this field from different aspects [34][35][36]. In this systematic review, it is aimed to contribute to the literature from different perspectives by including variables such as the content, type and duration of the physical activity which can directly affect the success of the school-based programs and are not sufficiently emphasized in other systematic review studies. Additionally, more studies are needed to evaluate the different contexts regarding the potential of school-based interventions. In this context, the study aims to systematically examine the possibility of school-based interventions for preventing obesity and promoting PA and PF.

Materials and Methods
The framework used analytically by Kahn et al. [37] and modified by Demetriou and Honer [30] was organized and used particularly in this study. In this sense, the expected characteristics of the school-based interventions, the expected outcomes and the interventions that are accepted to be used outside of PA in such programs are presented in Figure 1. The systematic review does not include content that violates human rights, in compliance with the Helsinki Declaration; therefore, ethical approval was not needed.

Literature Search and Study Selection
In order to fully incorporate the relevant literature, a thorough electronic screening was conducted. The following databases were used to scan the data: (1) PubMed, (2) Web of Science, (3) Scopus.
The scanning was focused on the following four key elements: population (children, adolescents), study design (trial), behavior (physical activity, walking, running, games, sports, etc.), and intervention (behavior change, higher BMI, level of physical activity, fitness). Focusing on these 4 elements, combinations of the terms school-based, physical activity, health, child, adolescent, intervention, overweight and obese were used in searching concepts (Supplementary File S2).
After the first screening based on databases, the title and abstracts were exported to an Excel file and records were screened by two researchers. At this stage, researchers excluded studies if they did not include physical activity and primary or secondary school students, and if it were not clearly indicated that the program was in a school setting. After the title and abstract review, the full texts of potentially related studies in the databases were recorded.

Eligibility Criteria
The main criteria used for inclusion in this study were the application of at least one of the programs presented in Figure 1 within the scope of school-based PA, and that the results of this intervention regarding at least one variable among the components of body composition, waist circumference, skinfold, PA level, and PF were measured. In addition to this, the studies consisted of primary or secondary school students as a sample and were published between the years 2010-2019, with English accepted as a criterion. Studies published in languages other than English were excluded. Besides, studies that did not take place within the scope of school-based PA and that did not involve intervention were excluded from the study even if the age group matched. The studies that did not include clear information regarding the measurement of outcomes about obesity and PA level or how PA was implemented were also excluded.

Data Extraction and Risk of Bias
The researchers initially summarized the abstracts of each article in the Excel file in order to serve the purpose of the research. At this stage, two different researchers examined the studies according to the criteria to be included in the study and articles that did not meet the criteria for inclusion in the study were extracted. The research design, population, intervention type, intervention details, data collection process, measured characteristics and findings of the studies remaining after this stage were filed. At the next stage, two independent researchers evaluated the quality of the full text of the studies through the "validated quality assessment tool for quantitative studies" developed in the Effective Public Health Practice Project (EPHPP) (Supplementary Table S1) [38].
The EPHPP quality assessment tool gives the six study components a strong, moderate or weak assessment (Table 1). Based on these ratings, a global quality rating is made. Powerful studies have no weak components. Moderate studies have only one weak component. Weak studies have two or more weak components.

Results
In the first screening based on databases, 395 studies (PubMed: 188, WoS: 134, Scopus: 73) were obtained. After the exclusion of 58 repeated studies, 337 remaining titles and abstracts were read and evaluated by the researchers. In addition, systematic studies were examined, and the 12 studies found were included in the review process at this stage. After the title and summary review, the full texts of 71 studies in the databases were recorded. Nineteen studies were included in the final process after the studies that did not fit the criteria were excluded following the full-text review. The process was summarized and presented in the PRISMA flow diagram [39] (Figure 2). Nineteen studies from 14 different countries (USA, Australia, England, France, Czech Republic, Iceland, Switzerland, Norway, Scotland, South Africa, China, India, Pakistan, Israel) met the eligibility criteria. 42.10% of these studies were identified as cluster randomized controlled trials, 21.05% as a non-randomized controlled trial, 15.78% quasi-experimental design, 10.52% randomized controlled trial and 10.52% as one-group, repeated measures design and mixed-effects model. An examination of the distribution of the schools studied revealed that 68.42% of the school-based intervention was realized in primary schools and 31.57% in secondary schools.

Description of Intervention and Study Quality
When the studies were evaluated according to the focus of the school-based program, the ratio of the physical activity-oriented studies (at least a direct intervention) was determined to be 73.68% and the ratio of the studies with education, guidance, counseling, and orientation support was determined to be 26.31%. The state of PA intervention being focused was evaluated according to whether it has a strategy or practice aimed at direct implementation of PA after the program details were examined. Among these studies, PA interventions have been in the form of increasing the duration of physical education or changing its content, performing extracurricular physical activities, doing activities during breaks or lunch breaks or giving activity breaks in the lessons other than physical education. In some researches, school-based interventions were in the form of examining the effects of a general project, while in some other researches it was in the form of directly intervening in a special group. In the control groups, nothing was changed. Two independent researchers helped to evaluate the quality of the studies. The results of the evaluation are given in Table 2. To examine the feasibility of the school-based program and its effect on blood pressure and body mass index among pre-adolescent girls.

Aperman-Itzhak et al. [41]
A non-randomized controlled trial To evaluate the effectiveness of a healthy lifestyle intervention on health knowledge, behavior, and anthropometric measurements.
To examine the 5-year impact of the program on preventing fat and improving PF and lifestyle.

Brown et al. [43]
A one-group, repeated measures design • 3290 children aged 4-12 years from southwest Scotland.
To examine body mass index standard deviation score changes following a Child Healthy Weight pilot intervention.

Carlson et al. [44]
Mixed-effects model To examine the effects of a multicomponent school-based intervention on anthropometric outcomes.

Hollis et al. [47]
Cluster randomized controlled trial To report the secondary outcomes of the study; to determine whether the intervention impacted on adiposity outcomes (weight, body mass index (BMI), BMI z-score.

Kipping et al. [48]
Cluster randomized controlled trial To investigate the effectiveness of a school-based intervention to increase PA, reduce sedentary behaviour, and increase fruit and vegetable consumption in children.

Kriemler et al. [49]
A cluster randomized controlled trial. To assess the effectiveness of a school-based PA program during one school year on physical and psychological health in children.

Li et al. [50]
Non-randomized controlled trial To assess the effectiveness of a school-based PA intervention during 12 weeks on obesity and related health outcomes in school children. To examine the impact of Energy Balance for Kids with Play (EB4K with Play), on students' PA, dietary habits and knowledge, and weight status over 2 years.
To assess the effects of a 2-year intervention program on body composition and objectively measured cardiorespiratory fitness.

Shore et al. [54]
A quasi-experimental design To determine the effects of a school-based pedometer intervention (SBPI) on daily accrued steps, academic performance, attendance, tardiness, and fitness performance in middle school students.

Sigmund et al. [55]
Non-randomized controlled trial • Four schools (2 control, 2 intervention) in the Czech Republic. To investigate the effect of increased PA on increasing daily PA and decreasing obesity in 6-9-year children. Besides, evaluation details are provided in the Supplementary Material. According to the evaluation results, 10 of the studies were evaluated as strong [40,47,49,50,52,[54][55][56][57][58] and the remaining nine studies were evaluated as moderate. There were no studies evaluated as weak. In the general evaluation, the studies where two researchers made different decisions were discussed by them and the final decision was made. The efficiency and details of the studies are presented in Tables 3 and 4. The "+" symbol indicates significant difference, the "−" symbol indicates no significant difference, and the abbreviation "NA" indicates that the relevant variable has not been examined in the study. The difference between systolic blood pressure (SBP), diastolic blood pressure (DBP) and BMI z scores (BMIz) of the experimental group and control group was found to be significant (1.9 mm Hg, 0.7 mm hg and 0.55 kg/m 2 ).

Aperman-Itzhak et al. [41]
Type: A healthy lifestyle intervention • Eating a healthy breakfast, drinking water, PA, and reading food labels.
• Safe and attractive playgrounds • Active play during break times Intensity: NA The intervention did not reduce BMI (kg/m 2 ) or the prevalence of overweight/obesity, but waist circumference was lower than the control group (p = 0.004).
• Nutrition education • Healthier school meals • Health and nutrition education for teachers, pupils, and families

Brown et al. [43]
A school-based pilot intervention   Body composition was not statistically significant (p > 0.05). Children in the intervention group increased their fitness by an average of 0.37 z score units more than the controls (p = 0.18). There was no significant difference in waist circumference and skinfold results (p > 0.05).

Shore et al. [54]
Step-Count Promotion • Self-monitoring through pedometer use

Step-count (steps/d) Intervention Group
Step-count (steps/d) Control Group Step-count promotion program significantly increased daily accrued step counts versus control (p < 0.05). Shuttle and mile run performance decreased from pre-to post-intervention in both groups.

PA: Caltrac accelerometer and Yamax Digiwalker SW-200 pedometer
There was a significant increase in daily activity levels compared to the control group (from 1718 to 3247 steps per day; and from 2.1 to 3.6 Kcal/Kg per day). The school-based intervention allows children to take more than 10,500 steps and reduces the risk of declined PA.

Thivel et al. [56]
PA program: • 120 min (two times for 60 min) of supervised physical exercise in addition to 2 h of Physical Education classes per week.
Significant improvement was observed in four (50%) of the eight studies (skinfold, waist circumference or digital measurement) in which body fat percentage was measured [41,42,49,50]; no significant difference was found in three studies (37.5%) [46,56,57]. However, while no significant difference was found in waist circumference and skinfold values in the study conducted by Magnusson, Hrafnkelsson, Sigurgeirsson, Johannsson and Sveinsson [53] (p > 0.05), the difference between the increases in fat percentage was found to be significant in favor of the experimental group (p < 0.05).
Obesity is also a variable directly related to the duration of intervention. In this context, when the studies lasting less than 6 months and the studies lasting longer than 6 months are compared according to the duration of the intervention [40][41][42]46,49,52,53,56], the success rate of the BMI variable was 62.5% (5/8); in studies less than 6 months [43,45,47,50,51,57] this rate was 66.66% (4/6). This result shows that shorter interventions can achieve similar success in the BMI variable.
In brief, it is understood that in almost half of the studies, there was an improvement in BMI (53.33%), waist circumference or skinfold (50%) values. It was determined that, in line with the type of intervention, the BMI variable improved significantly in 72.77% (8/11) of the physical activity-oriented studies and that a success rate of 50% (2/4) could be achieved in interventions focused on training, guidance, orientation or providing support.
Apart from that, while PA levels increased significantly in seven of the studies with the physical activity-oriented intervention [42,44,45,49,50,54,55], no significant development was observed in three of them [47,52,57]. Whereas PA levels increased significantly in one of the studies predominantly based on education and orientation [58], no significant increase was observed in the other two studies [48,51]. In addition, while PA levels increased significantly in two of the studies conducted through surveys [42,50]; the number of studies showing a significant increase in the studies measured by pedometer or accelerometer was determined to be four [49,54,55,58]. When evaluated in terms of duration, while a significant increase was observed in three of the studies where the intervention period lasted 6 months or less [45,50,54], no significant increase was observed in one study [51]. In the studies, which lasted over 6 months, while a significant increase was found in PA levels in five studies [42,44,49,55,58], development was not found to be significant in four studies [47,48,52,57].
In brief, although the type and extent of the interventions were different, PA levels of children increased in a significant proportion of the studies. While 70% (7/10) of the physical activity-oriented studies showed a significant increase, that 33.33% (1/3) success rate was achieved in studies focused on training and orientation. This result demonstrates the importance of applying PA strategies at the focus of the intervention program to increase the levels of PA.

Physical Fitness
In seven studies examined, components related to fitness were analyzed [42,45,49,[52][53][54]56]. As the first variable, the property of aerobic endurance was evaluated in terms of shuttle run, 1-mile run test and ergometer bike. It was concluded that in four of the studies examining the aerobic endurance, this variable increased significantly compared to the control group [45,49,53,56]. No significant development was observed in two studies [52,54]. Considering the type of intervention, significant improvement was observed in four intervention physical activity-oriented studies [42,45,49,56] and no significant improvement was observed in terms of aerobic endurance in two studies [52,54]. In the study, which was focused on education and orientation, significant developmental findings were found [53]. When evaluated in terms of intervention duration, the rate of studies that provided significant improvement in aerobic endurance in the intervention performed at 6 months or less was determined to be 66.66% (2/3) [45,56]. No significant difference was found in the study conducted by Shore, Sachs, DuCette and Libonati [54]. In studies with intervention over 6 months, the rate of studies, in which aerobic capacity increased significantly, was determined to be 66.66% (2/3) [49,53]. In the study conducted by Madsen, Linchey, Gerstein, Ross, Myers, Brown and Crawford [52], the change in the aerobic capacities of children was not found to be significant (p > 0.05).
Apart from aerobic endurance, four studies, most of which belong to health-related PF components, were examined in variables such as flexibility, speed, power, muscular strength and muscular endurance [42,45,54,56]. Among these, in the study conducted by Bhave, Pandit, Yeravdekar, Madkaikar, Chinchwade, Shaikh, Shaikh, Naik, Marley-Zagar and Fall [42], there was a significant improvement in favor of the intervention group in running, long jump, sit-up and push-up tests. In the study conducted by Eather, Morgan and Lubans [45], different variables related to PF were evaluated and significant improvement was observed in flexibility and muscular fitness properties in favor of the intervention group. In another study of Shore, Sachs, DuCette and Libonati [54], measurements were made regarding muscular strength, endurance and flexibility, but no significant difference was found compared to the control group. In the study where anaerobic capacity was measured in addition to health-related components, Thivel, Isacco, Lazaar, Aucouturier, Ratel, Dore, Meyer and Duche [56] found a significant difference in anaerobic fitness capacity in favor of the intervention group.
In brief, it is seen that in interventions based in school, measurements regarding all the health-related PF components (body mass index was examined in previous sections) were performed. Significant improvements were found in most of the studies predominantly focusing on aerobic capacity (66.66%). Improvements were observed in two of the three studies examining the different components of health-related PF. These improvements related to health-related PF parameters are valuable in terms of highlighting the importance of PA in improving children's health.

Discussion
The purpose of this systematic review is to examine the potential of school-based interventions for obesity parameters (BMI, waist circumference, skinfold), PA level, and PF. Overall, 18 of the 19 studies examined were able to achieve significant improvements in at least one variable. It can be said that the content and details of the school-based intervention program are the most important factors in determining the efficiency in the studies examined. When the studies were classified according to the focus of PA in the program details, in 14 studies a strategy for direct PA and focus within the program was found [40,[42][43][44][45][46][47]49,50,52,[54][55][56][57]. Additionally, in five studies, it was understood that the education, guidance, orientation, and support in material of the staff and teachers in subjects such as health, nutrition and healthy life were in focus [41,48,51,53,58]. When the variables examined are considered, it can be said that the success rates in the physical activity-oriented studies are higher in all variables compared to those that are multicomponent but not centered on PA. This reveals the necessity of centralizing strategies aimed at PA to prevent obesity, promote PA and PF. Of course, the priority of programs for lifelong PA and health should be to prepare appropriate learning environments. Health-based physical education curriculum models aiming at a physically active life lead to the preparation of appropriate learning environments [59]. However, the relationship between the curriculum and pedagogy needs to be well understood in order to adopt more available approaches and not to neglect the enjoyable aspects of school-based PA [60]. From a holistic perspective, school-based PA programs can be more successful in promoting PA and PF. Castelli et al. [61] listed some of the properties that schools should have in order to educate physically active children: (a) a holistic approach and (b) effective and diversified pedagogy. Measuring of multicomponent interventions involving environmental and educational strategies is a complex and challenging process [62]. In this sense, although evaluations of different variables were made in school-based PA studies, only variables related to physiological dimensions were considered in this systematic research in line with the purpose.
Health promotion was the primary emphasis in school-based intervention programs. When health was evaluated from the physical aspect, the importance of school-based PA programs in improving health was revealed in this study. Similarly, in the systematic review made by Naylor et al. [63], most of the school-based intervention studies (11/15) were found to be positively associated with at least one health outcome. Of course, any program structured so as not to compromise health in relation to PA will contribute positively to health, but programs that are more comprehensive, centered on PA and games can be more helpful in this sense. In support of this situation, in the systematic study conducted by De Bourdeaudhuij et al. [64], it was suggested that the school environment should be rendered appropriate for PA, and PA durations should be increased in order to promote health. It would be more appropriate to integrate school-based programs into curriculum models in health promotion [59]. Curriculum models will ensure the persistence of effective and cognitive learning, which is crucial for the development of healthy living habits [65,66].
In eight of the 15 studies that evaluated obesity-related parameters, significant improvements were observed in variables such as BMI, skinfold, waist circumference and body fat; in seven studies, no significant development was observed regarding the whole group. In this sense, failure to achieve full success in almost half of the studies (46.66%) reveals that both the applied program and environmental conditions should be re-evaluated. Regarding this issue, in some systematic studies examining the effect of school-based PA on obesity parameters, it was concluded that it has no positive effect [23,67]. Although PA interventions are of great value in terms of short-term benefits in the fight against obesity or overweight, comprehensive programs are needed to have healthy living habits in the long term. At this point, it was understood that in most of the studies conducted to prevent obesity, multicomponent programs focusing on more than one dimension were applied [64,68]. These multicomponent programs should focus on content, teacher training and curriculum design to help children learn knowledge, skills and attitudes. In the study conducted by Brown and Summerbell [69], it was stated that the combination of programs based on nutrition and PA might be more effective in the struggle with obesity in the long term. For a more effective and permanent solution against the struggle with obesity, such comprehensive programs should include at least 60 min of MDVA, and interventions should be aimed at healthy diet and healthy living habits. Regarding the duration of the intervention, there was no difference in efficiency between the studies that lasted less than 6 months and more. In a meta-analysis by Harris et al., the shorter or longer duration of the intervention did not change the outcome of obesity [23].
Significant reductions in PA levels increase the importance of schools in providing a diversity of PA. In this sense, the use of different types of physical activities in school can increase children's interest and encourage them to be more active [70,71]. In our study, improvement has been achieved in eight (61.53%) of the 13 studies aimed at increasing the level of PA. Similarly, in the systematic compilation conducted by Demetriou and Honer [30], it was concluded that in PA interventions in the school environment, 56.8% success was achieved in terms of increasing the level of PA. In the studies, in which PA intervention was predominantly in the center, development success on PA level reached higher rates (70-33.33%). An increase in the level of PA is important in every aspect, but when considered in relation to health, it is also important to indicate the intensity of PA. PA for at least 60 min per day with MDVA is suggested in order to improve health [3,6]. As interventions are very heterogeneous in terms of type, intensity and extent, there are difficulties in evaluating them at the point of MVPA. However, school-based PA programs have the potential to provide MVPA with high-intensity activity types [4]. In some of the studies evaluating the intensity of PA, interventions were found to be associated with MVPA [44,48]. Fairclough and Stratton stated that students engaged in MVPA for 27% to 47% of physical education class time [72]. To increase the intensity and duration of PA, it should be ensured that children are active when coming to school in the morning, during the break time, lunch break, in other lessons or at the extracurricular activities other than the physical education class. Physical education can be an effective influence on promoting PA [73]. Physical education courses should be the most complementary part of school-based PA, but this course only is not sufficient and more comprehensive programs are needed for lifelong activity [73]. The use of school-based interventions to increase the PA level of today's children is very valuable. Some studies clearly demonstrate this potential [74,75].
The last variable considered in the study was the concept of PF. In seven of the studies conducted on this subject, components related to PF were evaluated and positive developments were observed in many of these studies. The primary objective of school-based PA programs is to reach and maintain health-related PF. Therefore, in the studies reviewed, the focus was rather on health-related fitness components. These are factors including components such as health-related PF, BMI, cardiorespiratory endurance (aerobic endurance), muscular strength, muscular endurance and flexibility [8]. While the feature that is mainly desired to be improved in the studies examined is aerobic endurance, it was found that there were also evaluations regarding the other components. In some studies, conducted in this sense, there are findings concerning the potential of school-based programs in improving PF [29,76]. There are also studies demonstrating the potential of the developed curricula for fitness education [59,77]. The results of our study show that even if the programs are multicomponent, the way of PA intervention is the most decisive factor at this point. In this sense, PA and games are essential for promoting PF in such programs [78].
The problems in evaluating the efficiency of such studies include: (1) the presence of very heterogeneous groups in general, and (2) the implementation of many interventions without adequate supervision, focusing only on guidance in schools, not long-term, and some of the measurement methods used are not objective. In order to prevent these problems, programs should be continued from preschool to the end of high school so that children have lifelong healthy living habits and they also should be based on a theoretical framework. The results obtained indicate that school-based intervention programs can have important potential for preventing obesity and promoting PA and PF if these problems are overcome and they focus more on PA.
The limitations of this study can be classified as follows: (1) In this research, publications other than articles (theses, papers, books, etc.) and studies published in languages other than English were not included. (2) Although many variables are measured in school-based PA programs, it was focused only on measurements related to obesity, PA, and PF in this study. (3) Since the contents and the type of implementation of PA programs are generally multi-component, it is difficult to understand what the most effective way is in such studies. (4) Evaluation of the focus of school-based intervention programs was determined according to the details given in the articles. (5) Besides, some variables were measured by questionnaire and some studies did not provide enough details. (6) In this study, variables such as curriculum, teaching models and teacher competencies related to the learning process in PA, and PF developmental processes were excluded.

Practical Implications
The main purpose of the studies related to school-based PA programs and should be used to develop the motor skills necessary for children to be active throughout their lives, and also to educate children who exhibit positive social behaviors while improving their PA and fitness levels. In this sense, physical education teachers such as school sports leaders should consider different learning domains and include administration, family and other courses in the programs. Health professionals or experts should carry out PA interventions with sports scientists. In most of the studies examined, it was seen that the intensity of exercise was not planned before the interventions. In order to increase health-related contributions, interveners need to pay attention to this issue. Nowadays, school time is more precious than ever. Sports scientists should have more contact with this field and participate more actively in designing school-based intervention programs.

Conclusions
School-based interventions can have important potential in the health promotion of children in terms of obesity, PA level and PF. However, the quality, duration, and priority of PA intervention in comprehensive school-based programs and teacher capacity are some of the most important factors for preventing obesity and promoting PA and PF. If more impact is desired in school-based intervention programs, the focus of the program should be PA and, as far as possible, physical activities should be implemented directly. To prevent obesity and to promote PA and PF, the characteristics of more effective programs should be examined in detail and appropriate intervention programs should be designed. Such programs should be multicomponent and longitudinal to foster children's lifelong PA habits. This habit requires knowledge, skills and attitudes. Our study focuses on the aspect of skill (physical). Furthermore, future studies should also focus on knowledge and attitudes in order to demonstrate holistic understanding. At the same time, for children to adopt a habit of PA, issues such as motivation, physical competence and interaction with the environment, which are at the basis of the cycle according to physical literacy, are also important. In this sense, the role of school-based interventions in improving children's physical literacy should also be examined. Author Contributions: H.S.Y. participated in study design and conceptualization, contributed to methodology, validation, original draft preparation, and review and editing. F.N.Ş. contributed to the methodology and original draft preparation. N.M. contributed to the investigation, analysis, and data curation. P.D. contributed to the investigation, analysis, and visualization. A.B. participated in review and editing, contributed to visualization and supervision. The final manuscript has been approved by H.S.Y., F.N.Ş., N.M., P.D., and A.B. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.