The objective of this review was to systematically synthesize the results of original studies on the association between physical activity and social support in adolescents, published until April 2011. Searches were carried out in Adolec, Eric, Lilacs, Medline, SciELO, Scopus, SportsDiscus and Web of Science electronic databases and the reference lists of selected articles. Searches for articles, data extraction and assessment of methodological quality were conducted independently by two reviewers. In total, 75 articles met inclusion criteria and were analyzed. Most studies were published over the past 6 years (2006-11), conducted in high-income countries, with a cross-sectional design, using subjective measures of physical activity (e.g. questionnaires and recall) and exhibited medium to high methodological quality level. Social support was positive and consistently associated with the physical activity level of adolescents in cross-sectional and longitudinal studies. Those who received more overall social support as well as support from both parents, friends and family showed higher levels of physical activity. It is concluded that social support is an important factor associated with physical activity level in adolescents and should be targeted in intervention programs that aim to increase physical activity levels in this population group.

Parents and friends have a social influence on adolescents' level of physical activity through the mechanism of behavior modeling or through social support, mediated by self-efficacy.

Objective: To determine the prevalence of excessive screen time and to analyze associated factors among adolescents. Methods: This was a cross-sectional school-based epidemiological study with 2874 high school adolescents with age 14---19 years (57.8% female) from public and private schools in the city of João Pessoa, PB, Northeast Brazil. Excessive screen time was defined as watching television and playing video games or using the computer for more than 2 h/day. The associated factors analyzed were: sociodemographic (gender, age, economic class, and skin color), physical activity and nutritional status of adolescents. Results: The prevalence of excessive screen time was 79.5% (95%CI 78.1---81.1) and it was higher in males (84.3%) compared to females (76.1%; p<0.001). In multivariate analysis, adolescent males, those aged 14-15 year old and the highest economic class had higher chances of exposure to excessive screen time. The level of physical activity and nutritional status of adolescents were not associated with excessive screen time. Conclusions:The prevalence of excessive screen time was high and varied according to sociodemographic characteristics of adolescents. It is necessary to develop interventions to reduce the excessive screen time among adolescents, particularly in subgroups with higher exposure. Comportamento sedentário; Atividade motora; Obesidade Prevalência de tempo excessivo de tela e fatores associados em adolescentes Resumo Objetivo: Determinar a prevalência do tempo excessivo de tela e analisar fatores associados em adolescentes. Métodos: Trata-se de um estudo epidemiológico transversal, de base escolar, com 2.874 adolescentes de 14 a 19 anos de idade (57,8% do sexo feminino), do ensino médio das redes pública e privada no município de João Pessoa, PB. O tempo excessivo de foi definido como assistir televisão, usar o computador e jogar videogames por mais de duas horas por dia. Os fatores associados analisados foram: sociodemográficos (sexo, idade, classe econômica, cor da pele), prática de atividade física e estado nutricional do adolescente. Resultados: A prevalência de tempo excessivo de tela foi de 79,5% (95%IC: 78,1---81,1) e mais elevada no sexo masculino (84,3%) comparado com o feminino (76,1%; p<0,001). Na análise multivariada, verificou-se que os adolescentes do sexo masculino, de 14 a 15 anos idade e aqueles que pertenciam às classes econômicas mais altas apresentaram maiores chances de exposição ao tempo excessivo de tela. O nível de atividade física e o estado nutricional dos adolescentes não se associaram ao tempo excessivo de tela. Conclusões: A prevalência do tempo excessivo de tela foi elevada e variou com as características sociodemográficas dos adolescentes. Faz-se necessário desenvolver intervenções para reduzir o tempo excessivo de tela entre os adolescentes, particularmente nos subgrupos com maior exposição.

Objective:To determine the prevalence of excessive screen time and to analyze associated factors among adolescents.Methods:This was a cross-sectional school-based epidemiological study with 2874 high school adolescents with age 14-19 years (57.8% female) from public and private schools in the city of João Pessoa, PB, Northeast Brazil. Excessive screen time was defined as watching television and playing video games or using the computer for more than 2 h/day. The associated factors analyzed were: sociodemographic (gender, age, economic class, and skin color), physical activity and nutritional status of adolescents.Results:The prevalence of excessive screen time was 79.5% (95%CI 78.1-81.1) and it was higher in males (84.3%) compared to females (76.1%; p<0.001). In multivariate analysis, adolescent males, those aged 14-15 year old and the highest economic class had higher chances of exposure to excessive screen time. The level of physical activity and nutritional status of adolescents were not associated with excessive screen time.Conclusions:The prevalence of excessive screen time was high and varied according to sociodemographic characteristics of adolescents. It is necessary to develop interventions to reduce the excessive screen time among adolescents, particularly in subgroups with higher exposure.