The world-wide epidemic diffusion of obesity and the health and socio-economic implications of it has promoted extended research during the last decades on the aetiopathogenesis, treatment and prevention of this disease. The objective of the current paper is to review the existing literature on childhood obesity, focusing primarily on the role of physical activity, both in the pathogenesis and the treatment of the disease. Both the cross sectional and the prospective studies reviewed are quite consistent in demonstrating a relationship between obesity and physical activity in children. Furthermore the findings of the experimental studies are supportive to this relationship indicating that enhanced physical activity through structured exercise programmes, is an effective tool in treating childhood obesity. This tool can be even more effective if diet is also included as a component of the intervention.

However, the long-term benefits of such interventions are questionable and definitely not cost effective if they have to be implemented in large group of children. Understanding human behaviour and the role of family and school in the development of life habits, seems to be the key point in developing effective interventions with long term benefits. During the last two decades several school based programmes, with extended parental involvement, focusing both on developing healthy eating habits and increasing voluntarily physical activity, indicate a promising, effective approach without requiring substantial school time or new resources.

Bahrain Med Bull 2000;22(3):

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   * Kellogg’s Science and Nutrition Manager
 ** Professor of Sports and Exercise Science
      University of Ulster
      Northern Ireland.
***Professor & Director
      Preventive Medicine and Nutrition Clinic
      University of Crete.

The increased levels of adult inactivity, observed during the end of the century, seems to be highly related with the increased levels of obesity and chronic disease morbidity and mortality observed both in developed and developing world1,2,3. This relationship is also supported by research evidence showing a reduction in age standardized mortality rates in initially sedentary men who became more active4,5.

Furthermore, it seams that both the behavioral parameters (diet and physical activity) and physiological parameter (obesity) leading to increased risk for chronic diseases have their roots in childhood6,7. Specifically, it has been reported that life long physical activity is more likely to be initiated in childhood and adolescence8 and the physical activity levels in
 
 

adulthood are positively correlated with those during childhood8,9. The purpose of the present paper is to review scientific evidence focusing primarily on the role of physical activity and diet on both the etiology and the prevention of childhood obesity.

Is Children’s physical activity/inactivity related to childhood obesity?

Although there are accumulating evidence about the importance of genetic factors and the role of leptin in the development of obesity the non-genetic factors still remains the primary determinants. Precisely, when the energy expenditure is constantly lower than the energy intake over a long-term period this is leading to the development of overweight and obesity.The main components of energy expenditure are the resting metabolic rate, the thermic effect in food and the thermic effect of physical activity. Resting metabolic rate constitutes 60-70%, the thermic effect of food approximately 10% and the remainder is due to physical activity10. While the former two components are relatively constant the thermic effect of physical activity is most variable, suggesting that the main factor determining the levels of energy expenditure are the levels of physical activity.

When physical activity is measured as energy expenditure then it is necessary to adjust activity energy expenditure for body weight. This is because heavier children spend more energy for a certain activity compare to the lean children. Consequently in order to avoid misleading interpretation of the findings this correction needs to take place. An extra problem then arises regarding the appropriate correction factor. Children tend to do several activities that vary in nature (running vs cycling) regarding how much of the body weight is supported externally. Furthermore, Prentice et al11 suggested that the correct exponent is itself dependent on the relative mix of weight-dependent and non-weight dependent activities undertaken. Consequently an exponent closer to 1.0 might lead to over correction while an exponent closer to 0.5 might be more appropriate for sedentary lifestyle.

The different correction methods used in cross-sectional and prospective Double Labeled Water studies might be some of the reasons that these studies reached controversial findings and no clear conclusion can be reached12-15. Observational studies, although they are less objective, they might promote a more clear picture of children’s physical activity. Cross-sectional and prospective studies can guide us to the development of certain hypothesis. However, causal relationship can only be supported by experimental studies. For this reason studies falling is these two categories will be presented separately in the following section.

Cross-sectional

In a nationally representative cross-sectional survey in USA which took place between 1988 and 1994 on 8 to 16 year old children it was found that 20% of US children participated in 2 or lower bouts of vigorous physical activities per week. The rate was found to be higher for girls compared to boys (26% VS 17%). Overall 26% of the children were watching 4 or more hours of television per day while the highest rate was observed among non-Hispanic black children (24%). Both boys and girls who watch 4 or more hours of television per day had significantly greater body fat and body mass index compared to those who watched less than 2 hours per day16.

In agreement with these findings are the results of the study conducted by Obarzanek et al17 on 2379 black and white US children aged 9-10 years. Obarzanek et al, apart from hours of TV watching they also assessed daily physical activity with the use of 3 day activity diaries and dietary intake with the use of 3 day food records. With the use of multivariate – regression analysis they found that the variations observed in body mass index and sum of skinfold thickness can best be explained by hours of TV watching for both black and white girls and by the intake of saturated fat in black girls and intake of total fat in white girls.

Further more physical activity data was found to have a significant impact on the model explaining the variations obtained in the obesity indices only for black girls. Finally, it was found that black girls spent significantly more hours per week watching TV and video than white girls.

More or less in line with the above findings are the results of a study conducted on 712, 9-16 year old children from a low and middle income town in the Mexico City area18. They found that the mean time spent by children on TV watching (including video) was 4.1 ± 2.2 hours/day while the average time spent on moderate and vigorous physical activities were 1.8 ± 1.3 hours/day. Odds ratio of obesity were 12% higher for each hour of TV watching per day and 10% lower for each hour of moderate/vigorous physical activity per day.

In a small sample of 86 healthy 19 years old adolescents no differences were observed in body mass index between active and less active adolescents. However body composition (assessed based on an equation using arm circumference and tricep skinfold) was found to be significantly different and in favor of active adolescents compared to less active.Finally TV watching was found to be significantly and positively correlated to body mass index, tricep and subscapular skinfolds19.

In the Belgian Luxemburg child study 1028 children from the mainly rural area of the Province de Luxemburg in Belgium were examined. It was found that boys participated significantly more frequently in sport activities than girls did. A significant positive relationship between body mass index and time spent on TV watching daily was found (only) for boys, while participation in sports activities was found to be negatively related to subscapular skinfold. In girls no such relationships were found. Furthermore for both boys and girls it was found that father’s education was directly associated with participation in sports, whereas the mother being a housewife showed a negative relationship to physical activity and positive to TV watching of their children20.

In Thailand, in a study conducted by Mo-suwa and Geater21, 2161 primary school children aged 6-13 were examined. According to weight for height measurement, the prevalence of obesity was found to be 14.1%. With the use of logistic regression, childhood obesity was found to be significantly positive correlated with family income and negatively with family size. Furthermore the highest attributable factors for childhood obesity were found to be family history of obesity (34%), low exercise levels (12%) and an obese or overweight mother (10%).

In a study conducted in United Arab Emirates 566 female students from the Local University were examined. Students were classified as overweight when their weight was 110-120% of the reference weight for height and they were classified as obese when their weight exceeded 120% of the reference value. According to this criterion 10.8% of the students were classified as overweight and 30.6% as obese. Obesity was found to be associated with obesity during childhood, presence of obesity among one or both parents and food intake between meals. Limited physical activity and long afternoon napping were found to be important contributors to the development of obesity22.

Similar findings were obtained from a younger population in the same country. 220 children aged 6-18 years were divided into two groups (obese and non-obese) according to the body mass index (>90th percentile of age-sex reference data). The logistic regression analysis showed that family history of obesity, diet, physical activity and mother’s education were significant factors for the development of obesity. No relationship between socio-economic status and obesity was found23.

The same methodological approach was also used in another study conducted in Kuwait on 460 obese and 460 normal weight controls, 6-13 year old children. The logistic regression analysis showed that childhood obesity is significantly related to family history of obesity. However, no such a relationship was found for physical activity and parental social class24.

Comparisons between obese and non-obese children were also done in two recent studies. In Finland 129 obese children were compared with 142 normal weight controls. It was found that children’s obesity was negatively associated with children’s habitual physical activity and parent’s obesity (body mass index ³30 kg/m2). Also parent inactivity was a strong positive predictor of children’s inactivity25.

In Japan a matched-pair comparison was performed between 427 obese (body mass index ³18) and 854 control children. All children were 3 years old. It was found that parental overweight, children’s overweight at birth, snacking irregularity and physical inactivity are influencing factors for the development of obesity at the age of three26.

In an attempt to identify possible difference regarding cardiovascular disease risk factors between urban and rural areas of USA, 962 urban and 1151 rural third and fourth grade children were examined. It was found that although both body mass index and sum of skinfolds was significantly greater for rural children no differences were found between the two populations regarding physical activity27.

No relationship between physical activity and body weight was also found in a study conducted on an ethnically diverse, low income, urban school children population aged 9-12 year old in Canada28. Similarly, neither physical activity nor high fat food intake were found to be related to childhood obesity in a study conducted on 8-10 years old USA children29.

Prospective Studies

In a study conducted by Klesges et al30, 146 children and their families were followed for 3 years. Children’s average age at the beginning of the study was 4.4 years. It was found that increases in children’s leisure physical activity were associated with decreases in subsequent weight gain. It was also found that although parents’ BMI was related to children’s BMI, this parameter accounted less compared to children’s dietary intake and physical activity in determining changes in children’s BMI.

Similar are the findings of the well-known “Framingham children’s study”. In a paper published by Lynn et al31 the data obtained from 97 healthy children, aged 3-5 years at their entry of the study and re-examined at the 1st grade are presented. The data analysis showed that more active children (those with above-median activity levels) gained substantially less subcutaneous fat than did the less active children. When age, television viewing, energy intake, baseline triceps and parent’s body mass indices were controlled for, it was found that the less active children at baseline were 3.8 times as likely as active children to have an increasing triceps slope during follow up.

In a study conducted by Eck et al32, 92 children with one or two parents overweight and 95 children non of the parents being overweight were followed for one year. Average age for both groups at base line was 4.5 years of age and no differences regarding both weight, were observed for the two groups at baseline. At the follow up it was observed that the group of children with at least one parent overweight gained more weight (P=0.05) while no significant differences were observed between the two groups regarding total energy intake or physical activity. However, the high risk group was found to consume a significantly higher percentage of energy from fat.

Both the cross sectional and prospective studies reviewed above are quite consistent in demonstrating an association between childhood obesity and levels of physical activity. However, because of the difficulty of measuring physical activity due both the uncertainty of what is meant by physical activity and the lack of a valid, widely accepted tool for measuring it, few definitive conclusions are warranted. Perhaps the most reasonable conclusion is similar to one reached in a prospective study of 10 year weight changes in a national cohort of adults33, that low physical activity leads to weight gain, while weight gain leads to further diminution of activity. This conclusion would imply that interventions which could either increase physical activity or decrease fatness would turn the cycle in the favorite direction. In the next section the experimental studies would be reviewed looking for more solid evidence to support the causal relationship between physical activity and obesity.

Experimental studies

Supportive evidence for the value of exercise early in life for the prevention or treatment of obesity comes from experimental studies on animals34. Although it would be reasonable to formulate a hypothesis based on the findings of the animal studies it would be also wise to keep in mind the complexity of human behaviors and external parameters influencing it. For this reason in this section we will proceed with a step-wise approach presenting findings of controlled exercise interventions to more complex multidisciplinary approaches.

In a study conducted by Gutin et al35, 79, 7-11 year old, white, black and Asian children with obesity were randomly assigned to two groups. The first group was engaged in a controlled physical training for four months while the second group engaged in the physical training program the second four months. The physical training program offered in both groups, consisted of five 40 minutes sessions per week. Each session started with warm up and ended with cool down while the main part of the session consisted with at least 30 minutes aerobic activities at an indesity level of 70% of maximal heart rate. The findings of the study showed that both groups declined in percent body fat of an average 1.6% fat units during the training period. However the first group 4 months after the cessation of the training regained 1.3% of body fat35. Concluding, the finding of this study suggests that regular exercise without dietary intervention can improve the body composition profile of obese children. Furthermore it proves that obese children are capable of participating in a substantial amount of high intensity training over a long time period36,37.

A slight different approach was used in a study conducted by Epstein et al38 on 8-12 year old children from 61 families. It was found that interventions aiming to reduce sedentary lifestyle had higher, longer-term (after 1 year) beneficial effects on decreasing body fat compared to intervention focusing on reinforcing exercise. It was also found that the children participating in the mild form of intervention increased their liking for exercise and reduced their caloric intake compared to the children participating in the exercise-reinforcing group.

Although the short-term benefits of interventions focusing on exercise alone are clearly demonstrated in the above studies, the combination of dietary counseling plus exercise, is gaining more and more supporters world wide. The combination of exercise and dietary counseling has been followed in the studies reviewed bellow.

After 10 weeks of disciplinary intervention including guidance for dietary and exercise lifestyle changes on 59 obese children (mean age 2.8 ± 2.6) significant changes in total body fat mass but not in fat-free mass were observed39. No follow up was reported in this study.

Similar beneficial effects on a 10-week multidisciplinary intervention on 87, 7-17 years old obese children were reported in the study conducted by Sothern et al40. The intervention included a low calorie/high protein diet, moderate intensity progressive exercise program and behavior modification sessions. Significant favorable changes were observed in weight, body mass index, percent body fat and physical activity patterns both at the end of the intervention and in the one year follow up41,42. However no control group was used in the current study.

Supportive to the finding of the previous study are the findings of the study conducted by Johnson et al43. Similar multidisciplinary approach on obese children showed significant favorable changes on weight and their lipids profile right after the end of the 16 session intervention but also at the 5 year follow up compared to the control group.

More or less in line with the above studies are the findings of Schwingshandl et al44. In this study 30 obese children were divided into two groups. In the first group a strength training program and dietary counseling was applied where in the second group dietary counseling was applied alone. At the end of the intervention and at the one year follow up both groups improved significantly regarding body mass index. However the first group improved significantly compared to the second group regarding fat free mass.

A different approach has been tried in Thailand where 21 obese children aged 8-13 years joined a four weeks summer camp program. Exercise, swimming, group therapy and dietary restrictions during the official hours were implemented throughout the program. At the end of the program all participants had lost about 5% of their initial weight45. However, no long-term follow up has been reported from this study and whether these changes in body weight remained over time is not clear.

The findings of the above studies are consistent demonstrating favorable changes in the obesity indices of the intervention groups. However, none of these studies had a long-term follow up and it still remains questionable whether these positive changes will remain after the end of the intervention period. Further more, the absence or very limited involvement of the family jeopardize furthermore the sustainability of these results. Understanding the role of the family in the development of life habits and obesity, will help us to see the potential role that family could play in treating the problem and helping children in developing life long healthy habits. However the important role that family plays in developing children’s behaviors is generally recognized and is not a new theoretical concept46. The studies review bellow, have included families as part of their interventions.

In a very resent study conducted by Epstein et al47, ninety families with obese 8-12 year old children participated in a comprehensive family-based behavioural weight control program. These families were divided into four groups of intervention. All four interventions consisted of 6 months treatment period. Families received parent and child workbooks, which included introduction to weight control and self-monitoring the specific activity program, behaviour change techniques and maintenance of behaviour change. Periodically family members were weighted and they also attending 30-minute parent and child group meeting with individual therapist. The dietary intervention was the same for all four groups based on the Traffic Light Diet were foods are grouped in different colour groups according to their calories and nutrient content. The four interventions were varied only on the physical activity component of the intervention (emphasis on increasing physical activities VS decreasing sedentary activities) and treatment dose (low VS high). The families participating in the increase physical activity group were reinforced for increasing physical activities in addition to those engaged in at the onset of the program. Those participating in the decreasing sedentary activities group were reinforced for reducing sedentary behaviours that compete with being active. During the two years follow up it was found a significant reduction in children’s percent overweight and body fat and increase in aerobic fitness for all groups. Furthermore, obese participating parents showed a significant decrease in weight from base live to follow up. The finding of this study demonstrated that reducing sedentary behaviours through a family based weight control program can be as effective as a well validated activity in obese children, giving more flexibility for the therapists who are treating obese children.

Davis and Christoffel48, conducted one more study focusing on the dose response and the ideal age for applying an intervention on obese children. They divided 93 obese children (greater than 120% ideal body weight for height age) aged 1 to 10 years in four treatment groups defined by age (pre-school VS school age children) and frequency of visits in one year (two to three VS four or more). An individualised care plan including prescribed frequency and duration of exercise was applied for one year in all four groups. After one year of programme’s application it was found that all groups improved significantly regarding ideal body weight for height. However, the greatest changes were observed in the group with the pre-school age children with the frequent visits.

Similar encouraging findings have also being obtained from other studies applying family based programmes for obese US children with 10 years follow up49 and Chinese obese children with one year follow up50.

The findings of the studies presented above seems to indicate the positive effect of exercise, dietary counseling and the involvement of family in the treatment of childhood obesity. However, the cost of all these studies, if they have to be implemented in real life, would be tremendous since counselors and therapists would have to follow individual children and families for a quite long time. The need to develop effective, easy to implement interventions with access to large group of children and with low cost, is raising. The ideal environment for such interventions seems to be the school and a large number of studies have already tested the effectiveness and applicability of such interventions.
 

School based Interventions

The available studies applying school based interventions in order to promote physical activity and treat or prevent childhood obesity, among other coronary heart disease risk factors, can be grouped into three groups. Those focusing entirely on the enhancement of physical activity through the re-organization of the Physical Education (PE) classes. Those that focusing both on diet and physical activity, in and out of school, with no or limited parental involvement. And those which were focusing both on diet and physical activity promotion with enhanced parental participation.

Studies focusing on PE classes

During 70’s a new concept, regarding PE classes, is developing in USA, Canada and Australia, linking PE with physical fitness and the long-term promotion of health. It was believed that the more physical activity children do during PE classes the more physically active they will become after school and consequently they will adopt and track this life style into adulthood which could have a preventative action against coronary heart diseases51.

One of the first researches was executed in Canada and it is known as ‘The Trois Rivieres Study’. Five hours of PE classes, focusing on the promotion of cardiovascular fitness and strength, were added in the curriculum of 500 pupils aged 10-12 years old for four consecutive years. During the follow up it was found that the intervention group performed significantly higher in a cardiorespiratory fitness test compared to the control group which was taking only one 40-minutes PE class per week. It was also found that the amount of time devoted to moderate to vigorous activities daily was higher for the intervention group compared to the control due to more PE classes. However, it was found that control group children spent more time in moderate to vigorous activities out of school compared to intervention group52.

During the same time period another programme called ‘Vigorous Exercise Programme’ was applied in USA on 59 randomly selected school children aged 6-7 years old. These children participated in a 25 minutes well-structured aerobic exercise programme four times per week. At the end of the programme it was found that intervention group devoted significantly more time in activities elevating the heart rate above 160 bpm, both during PE classes and out of school, compared to the control group. However, no significant differences were found between groups in weight, height and skinfold thickness53.

Similar was the structure of the ‘Daily Physical Education’ programme applied in Australia on 10 years old for 14 weeks. Five hundred children were divided into three groups. The first two groups served as control groups and children participated in three 30-minutes PE classes per week, following the suggested curriculum from the Ministry of Education, or classes focusing mainly on the promotion of motor skills. The third group participated in a vigorous aerobic programme daily. At the end of the programme it was found that the group which participated daily in the aerobic exercise had a significant reduction in percent body fat and significant improvement in cardiorespiratory fitness compared to the control group54.

Recently a programme with similar structure was applied in Thailand. An exercise programme, in addition to the one hour PE class per week, consisted by a 15 minutes walk in the morning and a 20 minutes aerobic dance session, three times per week for 29.6 weeks was applies on 292 second grade elementary school children. The control group participated only in the one hour PE class per week. At the end of the intervention period no differences between the two groups were found regarding body mass index55.

Studies focusing on PE classes plus diet with no or limited parental involvement

One of the most recent and well-known programmes is the ‘Children and adolescent Trial for Cardiovascular Health’ (CATCH). This programme had three years duration and it was applied on third grade pupils. Certain changes regarding school lunch meals and PE classes were implemented in the intervention schools. The percentage of fat in the meals was reduced to 30% and the salt content of each meal was between 600-1000 mg, while at least 40% of the time during PE classes was devoted to moderate to vigorous physical activities. Intervention school children were also given a workbook where activities related to exercise, diet and smoking had to be completed at school or at home with parental involvement. At the end of the programme 2,366 intervention children and 1,653 control children were re-examined. It was found that although favorable significant changes were observed for the intervention group regarding both fat consumption and time devoted to moderate-vigorous physical activities, no differences were observed between groups regarding anthropometric indices56-59.
 

Similar structure had the ‘Cardiovascular Health in Children’ implemented in North Carolina. In this programme parental involvement was even more limited compared to CATCH. The total duration of the programme was eight weeks while the intervention group was consisted by 588 third and fourth grade pupils while the control by 686 pupils. At the end of the programme the only significant differences found between the two groups were on health knowledge and level of physical activity60.

Very similar structure with the previous programmes, but absolutely no parental involvement, was followed in a study conducted in Nebraska. The intervention had a total duration of two years while both intervention and control groups were consisted by children registered in third, fourth and fifth grade. At the end of the intervention period it was found that although intervention school lunches had significantly less fat and sodium and more fiber, according to the 24 hours dietary recall the only difference found between the two groups was for sodium. Physical activity during school hours was 6% greater for intervention group but out of school it was approximately 16% less compared to control group. Regarding body weight and body fat no differences were found between groups for both normal weight and obese children61.

Most of the above studies managed to increase children’s physical activity in the school setting. Further more some of them showed significant improvements in fitness. However, the short term benefits of all these studies regarding obesity indices or other cardiovascular risk factors are very limited or non. Furthermore it is questionable whether forms of interventions as those presented in the above studies can increase voluntarily physical activity out of school or even develop certain life style habits that could track into adulthood and help individuals to minimize the risk for cardiovascular diseases. The findings of Shephard et al52 and Donelly et al61 seams to indicate the opposite.

Similarly to the interventions out of the school setting, the ineffectiveness of the above studies seems to indicate the crucial role that family and parents can play in such interventions. The studies reviewed bellow have extended in their school based interventions to the parents/family setting.
 

Studies focusing on PE classes plus diet with parental involvement

The need to understand human behavior and the parameters influencing it was raised by more resent studies where parental participation was viewed as one of the main components of intervention. The first and most known programme of this kind was the ‘Known Your Body’ programme. The routes of this programme are back in 70’s62-64 and since then several versions of it has been applied in different regions of USA and other parts of the world.

Some of the most recent applications of the ‘Know Your Body’ programme in USA took place in New York, Houston and Michigan. In the New York and Houston programme the intervention group consisted of 2973 primary school children first to fourth grade, while the control group consisted of 1209 children. The duration of the intervention was 2 ½ years and it was consisted by activities that both children and parents had to do together at home, activities in the classroom, changes in the school lunch meals, promotion of leisure time physical activity. At the end of the intervention period significant favorable dietary changes  for the intervention group versus the control group were observed. No differences between the two groups were found for the body mass index65.

In the Michigan programme the intervention group consisted of 1200 pupils from all grades in four primary schools, while 500 pupils from four other schools served as the control group. After one year of intervention, significant favorable changes for the intervention group were found in dietary habits and levels of physical activity66.

In Israel the ‘Know Your Body’ programme was used for two years on a cohort of 242 first grade school children (both Hebrew and Arabs) while 161 pupils served as the control group. At the re-examination significant favorable changes for the intervention group were found in body mass index, serum blood lipids  and blood pressure67.

Similar favourable changes were found in Norway after two years of programme’s application on 828, 10-15 years old children68 and in Greece when the programme was applied for one year on 95, 13-14 year old children69.

More recently, in Greece, the main principles of the ‘Know Your Body’ programme were adapted in a ‘Health and Nutrition Education’ programme developed by the University of Crete. The programme had six years duration and it was applied to all children registered in first grade in 1992 in two counties of Crete, while the children from a third county served as control group. A representative sample of 602 pupils from the intervention counties and 444 from the control were examined for evaluation purposes at baseline, at the three years follow up and at the end of the intervention period, when children were at sixth grade. Significant favourable changes for the intervention group were found for the dietary habit, leisure time physical activity, anthropometric and serum lipids indices at the three years follow up70,71 and at the completion of the six years intervention72.

CONCLUSIONS

Both the methodological approaches of dietary restrictions and significant weight losses, whenever observed in the studies reviewed should be viewed with skepticism. As Quinzi73 stated children and adolescents should not be placed on restrictive diets because adequate calories are needed for proper growth and development. However, dietary guidelines and family based behavioral management plus exercise seems to be the three major components for treating childhood obesity.

On the same line is the review paper by Epstein and Goldfield74. According to their review there is not enough research data to evaluate the effects of exercise alone on treating childhood obesity. However, there is a sufficient number of studies in order to make a quantitative analysis on the comparison of diet versus diet plus exercise programmes. They suggested that exercise add to the effect of diet counseling in the short-term treatment of childhood obesity, which is in agreement with our review findings. In addition the main findings of the current review paper indicate that the ideal environment for large-scale interventions is the school setting but with extended involvement of the family too. Further more when such interventions are combined with the PE classes allow more hours of intervention with the least possible interference for the remainder of the curriculum. Such interventions provide an important model for school based health promotion for primary prevention of obesity and chronic diseases without requiring substantial school time or new resources.

Recent studies have shown that the degree of children’s participation in physical activities is very much related to the fun and enjoyment children get from their participation in the activity75-77. Furthermore, the enjoyment children get from their participation depends to a large extent on their perception of ability or self-mastery75,78. Children, who perceive that, have a low ability and feel unable to cope with the demands of the activity, are more likely to drop out78. For these reasons we might need to reconsider the objectives and the structure of the PE classes. PE classes should promote and encourage participation of all pupils of the intervention group and not just the few gifted ones79. It has been reported that training sessions of moderate intensity do not discourage the less gifted or the obese children, who actually are the ones that need most this type of intervention80,81.
 

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