Teses e Dissertações

• Teses
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Nível de atividade física aumenta entre meninos e diminui entre meninas Esse foi o resultado de um estudo feito pelos pesquisadores Samuel Dumith, Denise Gigante e Marlos Domingues, do Programa de Pós-Graduação em Epidemiologia da Universidade Federal de Pelotas, e que contou com a colaboração do pesquisador Harold Kohl, da Universidade do Texas, Estados Unidos. Foram entrevistados 4.120 adolescentes que fazem parte de um projeto chamado Coorte de 1993, o qual acompanha todos os indivíduos que nasceram em Pelotas, RS, no ano de 1993. Esses adolescentes foram visitados em suas casas em 2004, quando tinham 11 anos de idade, e em 2008 quando tinham 15 anos. Enquanto a maioria dos estudos mostra que existe um declínio da atividade física durante a adolescência, os resultados do estudo realizado em Pelotas mostram redução somente para as meninas, de 120 para 90 minutos por semana (redução de 25% dos 11 aos 15 anos). Por outro lado, os meninos da Coorte de 93 aumentaram sua atividade física, passando de 270 minutos por semana em 2004 para 330 minutos por semana em 2008 (aumento de 22%). Dessa forma, o aumento na prática de atividade física entre os adolescentes do sexo masculino pode ser visto como um resultado surpreendente e positivo. Um dado interessante, segundo Dumith, é que os adolescentes que não praticam determinada atividade aos 11 anos, dificilmente começarão a praticar após essa idade. Sendo assim, estimular o envolvimento em diversos tipos de atividades esportivas durante a infância e início da adolescência deveria ser uma prioridade de políticas públicas para promover a prática de atividade física. Outro resultado que merece destaque é que adolescentes ativos aos 11 anos têm mais chance de serem ativos aos 15 anos. Isso mostra que o comportamento futuro tem forte relação com o comportamento apresentado no passado, ao menos no que se refere à prática de atividade física. Os pesquisadores também investigaram os fatores responsáveis pela mudança da atividade física durante a adolescência. O principal fator, dentre os diversos estudados, foi o nível de atividade física da mãe. Os adolescentes cujas mães aumentaram a prática de atividade física tiveram mais chance de se tornarem ativos. Outro fator importante foi a maneira de criação do adolescente. Aqueles que foram criados mais soltos, comparados aos seus amigos, foram mais ativos do que aqueles criados mais dentro de casa. Algumas diferenças foram observadas conforme o sexo do adolescente. Entre os meninos, por exemplo, os que mais aumentaram a prática de atividade física foram os mais pobres. A hipótese para isso é que os mais ricos estão mais envolvidos em atividades sedentárias. Outro achado interessante é que os meninos que têm medo de morar no bairro têm menos chances de virem a ser ativos. Assim, cuidar da segurança do bairro pode contribuir para aumentar a prática de atividade física. Para as meninas, aquelas que tiveram sua menstruação mais cedo (antes dos 12 anos) tiveram maior redução no nível de atividade física do que aquelas que menstruaram mais tarde. Além das alterações hormonais dessa fase, as meninas mais maduras podem apresentar maior interesse por outras atividades e menor atração pela prática de esportes. Mas também é possível que as meninas mais ativas menstruem mais tarde. Outra variável importante para elas foi o tempo gasto na frente da televisão, videogame e computador. As adolescentes que aumentaram o tempo ocupado com tais atividades tiveram mais chance de se tornarem sedentárias dos 11 aos 15 anos. Este é o primeiro estudo no Brasil que investigou a mudança da atividade física na adolescência e os fatores responsáveis por esse evento. A pesquisa mostra dados inéditos e de grande importância para pais, professores, pesquisadores, gestores de saúde, órgãos públicos e privados. Os resultados completos desta pesquisa serão publicados em breve, em revistas especializadas, sob a forma de artigos científicos.


ARTIGOS

1- Physical activity change during adolescence: a systematic review and a pooled analysis

RESUMO: It is presumed that physical activity (PA) level decline during the lifespan, particularly in adolescence. However, currently, there is no study that quantifies these changes and pools results for a common interpretation.
Objective: To systematically review the literature regarding PA change during adolescence, and to quantify that change according to a series of methodological variables, exploring gender-and-age differences.
Data sources: Medline/PubMed; Web of Science.
Study selection: Longitudinal studies with, at least, two PA measures throughout adolescence (10 to 19 years old) or the first PA measure during childhood and the second one during adolescence.
Data extraction: Study project name, country, year of the first data collection, sample size, baseline age, follow-up duration, characteristics of the instrument (type, recall time, PA intensity and PA domain), unit of PA measure, and report of statistical significance.
Results: Overall, 26 studies matched the inclusion criteria. Most were carried out in the United States, assessed PA by questionnaire, and found a decline in PA levels during the adolescence. On average, the mean percentage PA change per year, across all studies, was -7.0 (95%CI: -8.8 to -5.2), ranging from -18.8 to 7.8. The decline was significant according to most sub-groups of variables analyzed. Although earlier studies revealed a higher PA decline in boys, the decline has been greater in girls in more recent studies (commenced after 1997). Moreover, although the decline among girls was higher in younger ages at baseline (9-12 y), it was higher in older ages (13-16y) among boys.
Conclusions: The decline of PA during adolescence is a consistent finding in the literature. Differences between boys and girls were observed, and should be explored in future studies. Interventions that attempt to attenuate the PA decline, even without an increase in PA levels, could be considered as effective.
Palavras-chave: physical activity; sports; adolescent; children; longitudinal studies

2- Physical activity prevalence and correlates among adolescents from Southern Brazil

RESUMO: The aim of this study was to evaluate the prevalence of physical activity and its correlates among adolescents aged 14-15 years.
METHODS: A cross-sectional study was carried out in Pelotas, Southern Brazil, comprising 4325 individuals from the 1993 Birth Cohort. Physical activity was analyzed using three approaches: 1) prevalence of any leisure-time physical activity; 2) prevalence of any active commuting to school; 3) prevalence of engagement in at least 300 min/wk of a combination of both. The correlates examined included demographic, socioeconomic, behavioral, social and biological factors, as well as the number of leisure-time physical activities practiced. Statistical analyses were done through Poisson regression.
RESULTS: The proportion of adolescents engaged in any leisure-time physical activity was 75.6%; and 73.4% were active commuters. Total physical activity prevalence (score  300 min/wk) was 48.2%, being higher for boys (62.6%) than girls (34.5%), and increasing linearly according to the number of physical activities performed (p<0.001). The correlates of physical activity according to the 300 min/wk threshold were: being non-white, having failed at school and time spent playing video games. Lower socioeconomic status, higher computer use and parents’ physical activity demonstrated association only among girls only.
CONCLUSIONS: Fewer than half of adolescents met the recommendations for physical activity, and this proportion tended to decrease among the wealthiest. Correlates of physical activity in adolescence differed according to the domain investigated (i.e. leisure time or transport). Engagement in a wide variety of physical activities should be encouraged since childhood.
Palavras-chave: Motor activity. Exercise. Sports. Adolescent. Prevalence. Epidemiology. Health promotion. Brazil.

3- A longitudinal evaluation of physical activity in adolescents: tracking, change and predictors

RESUMO: This longitudinal study aimed to: a) describe the change in leisure-time physical activity (LTPA) during early-to-mid adolescence; b) analyze the tracking of LTPA during this period; c) identify the predictors of LTPA change over the follow-up. The sample consisted of 4,120 adolescents from the 1993 Pelotas Birth Cohort, Brazil, who were followed from 11 to 15 years of age. LTPA was self-reported during home-based interviews, and measured in minutes per week (min/wk). Although boys increased their LTPA level over the four years (median=60 min/wk; P<0.01); a decrease was observed among girls (median=-30 min/wk; P<0.01). Kappa coefficients of participation in each kind of physical activity (PA) were weak. Either the probability to become engaged in a given activity during the follow-up or the probability to remain engaged in a given PA was low. However, the likelihood to be active at the end of the study was 50% higher (P<0.001) for those who were active at baseline. The main predictor of LTPA change was the number of physical activities performed at the age 11. Thus, an involvement in a variety of leisure-time physical activities should be encouraged since childhood. Finally, regular PA early in life can predict this behavior afterwards.

Palavras-chave: motor activity; exercise; sports; adolescent; child; cohort studies; developing countries; Brazil

4- Predictors of physical activity change during adolescence: a 3.5 years follow-up
RESUMO: The literature on determinants of physical activity (PA) among children and adolescents is still scarce and frequently conflicting. Thus, our objective was to investigate the predictors of changes in PA from early to mid adolescence in a cohort of adolescents.
Methods: This was a prospective study in Southern Brazil, conducted between 2004 and 2008. Overall, 4,120 adolescents were followed from 11 to 15 years of age. PA at baseline and follow-up was assessed with a questionnaire, administered through face-to-face interviews. The outcome was analyzed in two different ways: 1) the change in PA level in minutes per week (min/wk) between both observation points; 2) the PA trajectory in four groups (inactive-inactive, inactive-active, active-inactive and active-active) according to the recommended 300 min/wk threshold. Predictors evaluated were socio-demographic (race and socioeconomic level), biological (sexual maturation), environmental (exposure to outdoors while growing up and fear of living in the neighborhood), physical (body mass index), behavioral (screen time) and parental (maternal PA level) factors. Multiple linear regression and Poisson regression were used to analyze PA in its continuous and categorical form, respectively. Analyses were stratified by gender.
Results: Maternal PA change and more exposure to outdoors were directly associated with change in PA level (min/wk) for both genders. An inverse association was observed with socioeconomic level among boys. Higher maturation status (among boys) and later menarche were also directly associated with PA change. Predictors to remain inactive, compared to those who became active during the follow-up, were: socioeconomic level among boys (direct association); maternal PA (inverse association); more exposure to outdoors; fear of living in the neighborhood (among boys); and non-overweight girls. Predictors to become inactive, compared to those who remained active in both waves, were: socioeconomic level among boys (direct association) and change in screen time among girls (direct association).
Conclusions: This study demonstrates that social, family, biological, behavioral and environmental factors exert an important role in the PA change among youth as they move into adolescence. These findings may be relevant to the design of policies and intervention programs aimed at promoting PA in teenagers.