The impact of school-based physical activity programs on obesity prevention

This dissertation identified the most effective programs in the school environment aimed at combatting childhood obesity, provided evidence for the effectiveness of a long-lasting program at the population level, and offered evidence for a time-efficient intervention within physical education (PE) as a tool to improve fitness among students. It includes three distinct studies with related research questions and aims. 

Study 1 involved a systematic search of the literature performed to compare the effects of interventions that targeted reduction of sedentary behaviours or increase of physical activity (PA) or physical fitness on primary prevention of obesity in 6- to 12-year-old children. The search identified 146 reports that provided relevant data for meta-analysis. Point estimates in % body fat were higher for fitness interventions compared with PA interventions (standardised mean difference = −0.11%; 95%CI = −0.26 to 0.04, and −0.04%; 95%CI = −0.15 to 0.06). Including sedentary behaviour in a PA- or fitness-oriented intervention was not accompanied by an increase in intervention effectiveness as evidenced by the point estimates being slightly smaller compared with those for PA- or fitness-only interventions. Overall, the effects tended to be larger in girls than in boys, especially for PA + sedentary behaviour interventions. There was some evidence of inequality in that the effects on body mass index (BMI) were seen when interventions were delivered in the general population (standardised mean difference = −0.05, 95%CI = −0.07 to −0.02), but not in groups of disadvantaged children (standardised mean difference = −0.01, 95%CI = −0.29 to 0.19). 

Study 2 involved an examination of the effectiveness of a population-based, real-world, long-duration, PA intervention for children aged 6–14 in Slovenia, called Healthy Lifestyle. The intervention provided two or three additional lessons of PE per week. Although the focus was the improvement of physical fitness, it examined the intervention’s effectiveness from the perspective of body mass index (BMI) units decreased and obesity cases reversed. The study studied over 34,000 participants from the Healthy Lifestyle project/cohort and compared their results with a matched sample of nonparticipants from the same schools. It employed generalised estimating equations to assess the effects of different durations of exposure to the program on BMI (from 1 to 5 consecutive years of participation) in children who enrolled with normal weight, overweight, or obesity at the start of the program. The intervention group had a significantly greater reduction in BMI than did the control group across all participation durations and irrespective of baseline weight status. The largest effect was observed in girls with obesity at baseline, whose BMI was 1.4 kg/m2 lower after 3 years of intervention compared with controls. The reversal of obesity was more pronounced in girls for whom statistically significant differences were observed between the control and intervention group after 2 years (𝜒2(1,1112) = 5.776, p = 0.016), 3 years (𝜒2(1, 669) = 9.570, p = 0.002), 4 years (𝜒2(1, 343) = 5.107, p = 0.024), and 5 years of participation (𝜒2(1, 192) = 4.551, p = 0.033). In boys, obesity reversal-rate differences between intervention and control groups attained statistical significance only after 3 years (𝜒2(1, 766) = 6.435, p = 0.011) and 5 years (𝜒2(1, 198) = 4.863, p = 0.027) of participation. Also, the number needed to treat (NNT) decreased steadily with the duration of the program in both sexes, with generally lower numbers for girls. The lowest NNTs were seen for 5 years of participation in the program (NNT = 17 and 12 for girls and boys, respectively). The proportion of obesity cases stratified by intervention participation and sex across all five years was 5-7%. Notably, a reduction in intervention effectiveness was evident in the year the program was hindered by a lack of funding. Intervention was effective with the largest BMI reduction in children presenting initially with obesity, and smallest in normal-weight children, indicating that the PA intervention(s) were able to benefit the children needing it most. 

Study 3 determined the efficacy of a high-intensity interval training (HIIT) intervention lasting 12 weeks on the health-related fitness and adiposity of 10- to 15-year-old students implemented during PE. The focus of this study was to compare two approaches for increasing fitness level among adolescents, one approach focusing on regular PE sessions in accordance with the curriculum and the other on regular PE classes augmented by HIIT. A cluster randomised control trial (RCT) (pretest/posttest) was conducted. The total number of students across both groups was 207. I used general linear models to compare fitness and adiposity changes in both groups based on the Eurofit fitness test battery. A significant effect of the HIIT intervention was present for the 20-meter shuttle-run test scores (p = 0.001). The effect of the intervention compared with the control was estimated as an additional 181.2 metres, 95% CI (70.4 to 292.0). An additional intention-to-treat (ITT) analysis showed that the effect of the HIIT intervention on the 20-meter shuttle-run test remained statistically significant (p < 0.011), although the magnitude of the estimated effect was reduced from 181.2 meters; SE = 55.4 to 119.6 meters; SE = 46.4. The effect on the 20-meter shuttle run test scores occurred with a relatively low dose of HIIT in PE lessons undertaken twice a week. Whilst it appears HIIT had the opposite of the expected effect on body fat percentiles, the effect on body composition was inconsistent. The effect of the regular PE classes compared to HIIT intervention is estimated as 2.76 percentiles, 95% CI (0.3, 5.1), with lower values among controls. However, this was also no longer evident following the ITT analysis (from p=0.03 to p=0.086). The intervention is registered with the Australian New Zealand Clinical Trials Registry (ANZCTR) [ACTRN12622000209796]. 

The overall and final conclusion resulting from this dissertation is that school-based PA programs represent a powerful tool for obesity management and cardiorespiratory fitness (CRF) enhancement. Tailoring interventions toward increasing fitness among children and adolescents should be a priority because these interventions have a twofold benefit: 1) they are effective in preventing and treating obesity, and 2) if implemented using an HIIT approach, they can effectively increase CRF in a relatively short period of time. A scaled-up, long-lasting approach should be the goal of any intervention because this approach was shown to be effective not only for preventing obesity but also for reversing obesity among children and adolescents. The longer the intervention lasts, the more effective it becomes, especially for individuals who need the intervention the most, that is, those who suffer from obesity.