Objective To review the published literature on the effectiveness of interventions to promote physical activity in children and adolescents. Design Systematic review. Data sources Literature search using PubMed, SCOPUS, Psychlit, Ovid Medline, Sportdiscus, and Embase up to December 2006. Review methods Two independent reviewers assessed studies against the following inclusion criteria: controlled trial, comparison of intervention to promote physical activity with no intervention control condition, participants younger than 18 years, and reported statistical analyses of a physical activity outcome measure. Levels of evidence, accounting for methodological quality, were assessed for three types of intervention, five settings, and three target populations. Results The literature search identified 57 studies: 33 aimed at children and 24 at adolescents. Twenty four studies were of high methodological quality, including 13 studies in children. Interventions that were found to be effective achieved increases ranging from an additional 2.6 minutes of physical education related physical activity to 283 minutes per week of overall physical activity. Among children, limited evidence for an effect was found for interventions targeting children from low socioeconomic populations, and environmental interventions. Strong evidence was found that school based interventions with involvement of the family or community and multicomponent interventions can increase physical activity in adolescents. Conclusion Some evidence was found for potentially effective strategies to increase children's levels of physical activity. For adolescents, multicomponent interventions and interventions that included both school and family or community involvement have the potential to make important differences to levels of physical activity and should be promoted. A lack of high quality evaluations hampers conclusions concerning effectiveness, especially among children.

Physical activity and sedentary behaviour in youth have been reported to vary by sex, age, weight status and country. However, supporting data are often self-reported and/or do not encompass a wide range of ages or geographical locations. This study aimed to describe objectively-measured physical activity and sedentary time patterns in youth. The International Children’s Accelerometry Database (ICAD) consists of ActiGraph accelerometer data from 20 studies in ten countries, processed using common data reduction procedures. Analyses were conducted on 27,637 participants (2.8–18.4 years) who provided at least three days of valid accelerometer data. Linear regression was used to examine associations between age, sex, weight status, country and physical activity outcomes. Boys were less sedentary and more active than girls at all ages. After 5 years of age there was an average cross-sectional decrease of 4.2 % in total physical activity with each additional year of age, due mainly to lower levels of light-intensity physical activity and greater time spent sedentary. Physical activity did not differ by weight status in the youngest children, but from age seven onwards, overweight/obese participants were less active than their normal weight counterparts. Physical activity varied between samples from different countries, with a 15–20 % difference between the highest and lowest countries at age 9–10 and a 26–28 % difference at age 12–13. Physical activity differed between samples from different countries, but the associations between demographic characteristics and physical activity were consistently observed. Further research is needed to explore environmental and sociocultural explanations for these differences.

Background School-based interventions are thought to be the most universally applicable and effective way to counteract low physical activity (PA) and fitness although there is controversy about the optimal strategy to intervene. Objectives The objective of this review was to summarise recent reviews that aimed to increase PA or fitness in youth and carry out a systematic review of new intervention studies. Methods Relevant systematic reviews and original controlled and randomised controlled school-based trials with a PA or fitness outcome measure, a duration of ≥12 weeks, a sufficient quality and involvement of a healthy population aged 6–18 years that were published from 2007 to 2010 were included. Results In these reviews, 47–65% of trials were found to be effective. The effect was mostly seen in school-related PA while effects outside school were often not observed or assessed. Conclusions The school-based application of multicomponent intervention strategies was the most consistent, promising strategy, while controversy existed regarding the effectiveness of family involvement, focus on healthy populations at increased risk or duration and intensity of the intervention. All 20 trials in the review update showed a positive effect on in-school, out-of-school or overall PA, and 6 of 11 studies showed an increase in fitness. Taking into consideration both assessment quality and public health relevance, multicomponent approaches in children including family components showed the highest level of evidence for increasing overall PA. This review confirms the public health potential of high quality, school-based PA interventions for increasing PA and possibly fitness in healthy youth.

Many youth fail to meet the recommended guidelines for physical activity. Walking and cycling, forms of active travel, have the potential to contribute significantly towards overall physical activity levels. Recent research examining the associations between physical activity and the environment has shown that environmental factors play a role in determining behaviour in children and adolescents. However, links between the environment and active travel have received less attention.

Data are available on correlates of physical activity in children and adolescents, less is known about the determinants of change. This review aims to systematically review the published evidence regarding determinants of change in physical activity in children and adolescents. Prospective quantitative studies investigating change in physical activity in children and adolescents aged 4-18 years were identified from seven databases (to November 2010): PubMed, SCOPUS, PsycINFO, Ovid MEDLINE, SPORTDdiscus, Embase, and Web of Knowledge. Study inclusion, quality assessment, and data extraction were independently validated by two researchers. Semi-quantitative results were stratified by age (4-9 years, 10-13 years, and 14-18 years). Of the 46 studies that were included, 31 used self-reported physical activity; average methodologic quality was 3.2 (SD=1.2), scored 0-5. Of 62 potential determinants identified, 30 were studied more than three times and 14 reported consistent findings (66% of the reported associations were in the same direction). For children aged 4-9 years, girls reported larger declines than boys. Among those aged 10-13 years, higher levels of previous physical activity and self-efficacy resulted in smaller declines. Among adolescents (aged 14-18 years), higher perceived behavioral control, support for physical activity, and self-efficacy were associated with smaller declines in physical activity. Few of the variables studied were consistently associated with changes in physical activity, although some were similar to those identified in cross-sectional studies. The heterogeneity in study samples, exposure and outcome variables, and the reliance on self-reported physical activity limit conclusions and highlight the need for further research to inform development and targeting of interventions.