Abstracts

INTRODUCTION

High rates of global physical inactivity are negatively impacting population health.¹⁰10 Hallal PC, Andersen LB, Bull FC, Guthold R, Haskell W, Ekelund U. Global physical activity levels: surveillance progress, pitfalls, and prospects. Lancet. 2012;380(9838):247-57. DOI:10.1016/S0140-6736(12)60646-1^,1313 Lee I, Shiroma EJ, Lobelo F, Puska P, Blair SN, Katzmarzyk PT. Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. Lancet. 2012;380(9838):219-29. DOI:10.1016/S0140-6736(12)61031-9 Understanding the factors associated with physical activity practice is an essential step for planning interventions aimed at reducing the high rates of physical inactivity observed worldwide.⁴4 Bauman AE, Seis RS, Sallis JF, Wells JC, Loos RJF, Martin BW. Correlates of physical activity: why are some people physically active and other not? Lancet. 2012;380(9838):258-71. DOI:10.1016/S0140-6736(12)60735-1 Personal, environmental, physical, and social factors are recognized as important variables associated with physical activity practice.⁴4 Bauman AE, Seis RS, Sallis JF, Wells JC, Loos RJF, Martin BW. Correlates of physical activity: why are some people physically active and other not? Lancet. 2012;380(9838):258-71. DOI:10.1016/S0140-6736(12)60735-1

The Brazilian National Adolescent School-Based Health Survey (PeNSE) showed that 43.1% of students from the 9^th grade achieved the recommended levels of physical activity for youth.⁹9 Hallal PC, Knuth AG, Cruz DKA, Mendes MI, Malta DC. Physical activity practice among Brazilian adolescents. Cienc Saude Coletiva. 2010;15(2):3035-42. DOI:10.1590/S1413-81232010000800008 However, recent reviews reinforce the importance of intervention during adolescence, particularly through school programs,¹¹11 Hoehner CM, Ribeiro IC, Parra DC, Reis RS, Azevedo MR, Hino AA, et al. Physical activity interventions in Latin America: expanding and classifying the evidence. Am J Prev Med. 2013;44(3):31-40. DOI:10.1016/j.amepre.2012.10.026^,1919 Souza EA, Barbosa Filho VC, Nogueira JAD, Azevedo Jr MR. Physical activity and healthy eating in Brazilian students: a review of intervention programs. Cad Saude Publica. 2011;27(8):1459-71. DOI: 10.1590/S0102-311X2011000800002 because of the positive impact of being active on physical, social, and mental health⁵5 Bouchard C, Blair S, Hasko W. Physical Activity and Health. Champaign: Human Kinetics; 2007. and the increased chances of keeping active during adulthood.¹1 Azevedo MR, Horta, BL, Gigante, DP, Sibbritt, D. Tracking of physical activity in the 1982 birth cohort in Pelotas. Rev Bras Ativ Fis Saude. 2011;16(2):156-61.^,1212 Kjonniksen L, Anderssen, N, Wold B. Organized youth sport as a predictor of adulthood physical activity. Scand J Med Sci Sports. 2008;19(5):646-54. DOl: 10.1111/j.16oo-0838.2oo8.00850.^,1515 Malina R. Tracking of physical activity across the lifespan. Res Q Exerc Sport. 1996;67(3 Suppl):48-57.^,2020 Tammelin T, Näyhä S, Hillas AP, Järvelin MR. Adolescent participation in sport and adult physical activity. Am J Prev Med. 2003;24(1):22-8. DOI:10.1016/S0749-3797(02)00575-5^,2121 Telama R. Tracking of physical activity from childhood to adulthood: a review. Obes Facts. 2009;2(3):187-95. DOI:10.1159/000222244 Evidence on the tracking of active behavior, particularly during adolescence, suggests moderate stability of physical activity, although most of these studies have been conducted in high-income countries.¹⁴14 Lopes, VP, Maia, JAR, Silva, RG, Seabra, A, VAsques, CMS. Estabilidade e mudança nos níveis de actividade física: uma revisão da literatura baseada na noção e valores de tracking. Rev Bras Cineantropom Desempenho Hum. 2005;7(2):69-79.

The aim of the present study was to analyze physical activity during adolescence in participants of the 1993 Pelotas Birth Cohort Study, Brazil.

METHODS

In 1993, all maternity hospitals in Pelotas, RS, Southern Brazil, were visited daily and 5,265 newborns whose family lived in the urban area of the city were identified. A total of 5,249 mothers agreed to enroll their infants in the study.²²22 Victora CG, Hallal PC, Araújo CLP, Menezes AMB, Wells JCK, Barros FC. Cohort profile: The 1993 Pelotas (Brazil) birth cohort study. Int J Epidemiol. 2008,37(4):704-9. DOI:10.1093/ije/dym177 All participants were followed-up at 11, 15, and 18 years of age. Table 1 presents details of the participants at enrolment and at the 18-year follow-up. Further details on the study methodology have been published elsewhere.²2 Araújo CL, Menezes AMB, Vieira MFA, Neutzling MB, Gonçalves H, Anselmi L, et al. The 11 year follow up of the 1993 Pelotas (Brazil) birth cohort study: methods. Cad Saude Publica. 2010;26(10):1875-86. DOI:10.1590/S0102-311X2010001000003^,2222 Victora CG, Hallal PC, Araújo CLP, Menezes AMB, Wells JCK, Barros FC. Cohort profile: The 1993 Pelotas (Brazil) birth cohort study. Int J Epidemiol. 2008,37(4):704-9. DOI:10.1093/ije/dym177

Similar data were collected in 2004 and 2008 when the participants were, on average, 11 and 15 years of age. In both surveys, trained interviewers collected data during face-to-face home interviews. For quality control, 30.0% of the interviews were repeated (10.0% in person and 20.0% by phone call) using a short version of the questionnaire. The last set of data collection was performed in 2011 when the participants were 18 years of age. Different from the previous follow-up visits, in 2011, the participants were invited to our research center for interviews and measurements.

Leisure-time physical activity was self-reported in all interviews. At 11 and 15 years of age, adolescents were prompted to recall the duration and frequency of practicing a list of different activities during the past week. The list was constructed on the basis of a pilot study that identified the most frequent activities practiced at each age. The instrument showed moderate reliability (rho = 0.62) and concurrent validity (kappa = 0.58) in a validation study.³3 Bastos JP, Araújo CLP, Hallal PC. Prevalence of insufficient physical activity and associated factors in Brazilian adolescents. J Phys Act Health. 2008;5(6):777-94. The time spent on leisure-time physical activity was estimated from the weekly frequency and duration of each activity. Participants were considered active if they performed ≥ 300 min/week of moderate-to-vigorous physical activity.²³23 World Health Organization. Global recommendations on physical activity for health. Geneva; 2010. At 18 years of age, the participants answered the leisure-time section of the International Physical Activity Questionnaire (IPAQ), long version.⁷7 Craig CL, Marshall AL, Sjostrom M, Bauman AE, Booth ML, Ainsworth, BE, et al. International Physical Activity Questionnaire: 12-country reliability and validity. Med Sci Sports Exerc. 2003;35(8):1381-95. DOI:10.1249/01.MSS.0000078924.61453.FB The same cut-off point was used.

In data analyses, we determined the levels of physical activity and other independent variables. The Chi-square test was used to compare physical activity levels according to sex at each age point. Changes in physical activity levels over time were tested using the Chi-square test for linear trend.

Poisson regression was used to analyze the associations between physical activity levels at 11 and/or 15 years of age and the levels at 18 years of age after adjusting for confounding factors. To reproduce physical activity guidelines, we used categorical physical activity variables in the periods studied. Therefore, the use of Poisson regression provided us with the likelihood of being active at any age according to activity levels at the previous age point.

Analyses were stratified by sex and the significance level was set at 5%. Data on skin color were collected at 11 years of age. The household socioeconomic index was calculated using principal component analysis of a list of household assets (TV, car, radio, computer, DVD, internet, refrigerator, freezer, vacuum cleaner, and washing machine). The continuous score of the first component was divided into quintiles. The confounding factors included in the adjusted analyses were sex, skin color, and socioeconomic index.

The study was approved by the Comitê de Ética em Pesquisa da Faculdade de Medicina da Universidade Federal de Pelotas (Process 05/2011 – 2/22/2011). All adolescents and their parents signed an informed consent form.

RESULTS

At 18 years of age, a total of 4,092 adolescents (78.0% of the original sample) were interviewed and provided data on physical activity (Table 1). All categories based on sex and family income showed participation rates higher than 75.0%. Table 2 details the types of physical activities reported at 18 years of age. The mean walking time was about 1 h/week for both sexes. More than 50.0% of females were physically inactive (Table 2). A total of 3,736 participants provided data on physical activity at each of the three age points.

Figure 1 shows physical activity levels according to age. The analysis demonstrates that regardless of the study period, boys were more active than girls (p < 0.001), and there was a significant decrease in physical activity as age increased across the sample (p < 0.001).

Table 3 shows the prevalence ratios for being active during leisure time at 18 years of age according to physical activity levels at 11 and 15 years of age. In the adjusted analysis, participants who were active at 11 and 15 years of age were 58.0% (95%CI 1.39;1.80) more likely to achieve ≥ 300 min/week of physical activity at 18 years of age compared with those who were inactive at 11 and 15 years of age.

Figure 2 shows the maintenance of physical activity across the three age points. Considering all active participants at 11 years of age, 32.0% and 8.0% of males and females, respectively, remained active at 15 and 18 years of age. Analysis of all participants who were inactive at 11 years of age (Figure 3) showed that the proportion of participants who were consistently inactive was higher among females (66.0%) than males (31.0%).

DISCUSSION

The findings of the present study support the results of previous research that has identified declining levels of physical activity during adolescence. Furthermore, the results indicate that individuals active in early adolescence have a higher likelihood of being active in early adulthood. There is a strong stability of physical inactivity across adolescence, suggesting that interventions should start as early in life as possible.

The high proportion of participants who were followed-up at each age point reduces the likelihood of selection bias. Furthermore, data on confounders such as socioeconomic status were prospectively collected, minimizing the possibility of residual confounding or other biases.

Although there are limitations of using self-reported physical activity, both instruments used in this study have been validated prior to use in our cohort. The IPAQ has been used in several countries, enabling comparison with other contexts.⁸8 Hallal PC, Gomez LF, Parra DC, Lobelo F, Mosquera J, Florindo AA, et al. Lessons learned after 10 years of IPAQ use in Brazil and Colombia. J PhysAct Health. 2010;7(2):259-64. The positive validity indicators for both instruments suggest that physical activity levels reflect the reality, minimizing the likelihood of bias resulting from the use of different instruments. Although physical activity guidelines for adults recommend half the time suggested for adolescents,²³23 World Health Organization. Global recommendations on physical activity for health. Geneva; 2010. we used the same cut-off point (≥ 300 min/week) throughout the study to allow comparison at different ages.

The finding that physical activity levels decline during adolescence is consistent with the results of previous studies.⁶6 Brodersen NH, Steptoe A, Boniface DR, Wardle J. Trends in physical activity and sedentary behavior in adolescence: ethnic and socioeconomic differences. Br J Sports Med. 2007;41(3):140-4. DOI:10.1136/bjsm.2006.031138^,1616 Nelson MC, Neumark-Stzainer D, Hannan, PJ, Sirard JR, Story, M. Longitudinal and secular trends in physical activity and sedentary behavior during adolescence. Pediatrics. 2006;118(6):1627-34. DOI:10.1542/peds.2006-0926

17 Sallis JF. Age-related decline in physical activity: a synthesis of human and animal studies. Med Sci Sport Exerc. 2000;32(9):1598-600. DOI:10.1097/00005768-200009000-00012^-1818 Seabra AF, Mendonça DM, Thomis MA, Anjos LA, Maia JA. Determinantes biológicos e sócio-culturais associados à prática de atividade física de adolescentes. Cad Saude Publica. 2008;24(4):721-36. DOI:10.1590/S0102-311X2008000400002 Besides showing lower levels of physical activity at the beginning of adolescence, girls display a greater decrease in activity over time.²⁰20 Tammelin T, Näyhä S, Hillas AP, Järvelin MR. Adolescent participation in sport and adult physical activity. Am J Prev Med. 2003;24(1):22-8. DOI:10.1016/S0749-3797(02)00575-5 The present study shows that practicing physical activity according to the recommendations (≥ 300 min/week) at 11 and 15 years of age is associated with a 58.0% increased likelihood of achieving the physical activity recommendations at 18 years of age. Studies from the 1982 Pelotas Birth Cohort Study, which tracked physical activity at 15, 18, and 23 years of age, showed similar results.¹1 Azevedo MR, Horta, BL, Gigante, DP, Sibbritt, D. Tracking of physical activity in the 1982 birth cohort in Pelotas. Rev Bras Ativ Fis Saude. 2011;16(2):156-61.

It is relevant, but worrying, that tracking of inactive behavior is stronger than that of physical activity, particularly among girls. At 11 years of age, a large number of girls did not accomplish the physical activity recommendations, and they tended to continue being inactive throughout adolescence. Physical activity practice during adolescence is related to different determinants, including personal, social, cultural, and behavioral factors.¹⁷17 Sallis JF. Age-related decline in physical activity: a synthesis of human and animal studies. Med Sci Sport Exerc. 2000;32(9):1598-600. DOI:10.1097/00005768-200009000-00012^,1818 Seabra AF, Mendonça DM, Thomis MA, Anjos LA, Maia JA. Determinantes biológicos e sócio-culturais associados à prática de atividade física de adolescentes. Cad Saude Publica. 2008;24(4):721-36. DOI:10.1590/S0102-311X2008000400002 Several demographic variables linked to physical activity, such as sex, age, skin color, and socioeconomic status, were included in the present study as possible confounders. However, other determinants that can affect physical activity, such as competence perception, parental support, and availability of facilities, were not included in this study.

In Latin America, some initiatives have produced positive results.¹¹11 Hoehner CM, Ribeiro IC, Parra DC, Reis RS, Azevedo MR, Hino AA, et al. Physical activity interventions in Latin America: expanding and classifying the evidence. Am J Prev Med. 2013;44(3):31-40. DOI:10.1016/j.amepre.2012.10.026 The school is an important place to target investments to increase physical activity among students, and physical education classes play an important role.¹¹11 Hoehner CM, Ribeiro IC, Parra DC, Reis RS, Azevedo MR, Hino AA, et al. Physical activity interventions in Latin America: expanding and classifying the evidence. Am J Prev Med. 2013;44(3):31-40. DOI:10.1016/j.amepre.2012.10.026 Brazil needs to strengthen commitment and contributions to physical education at school using polices on physical activity and sports promotion.

Findings from the present study reinforce the evidence that promoting physical activity at early stages of life is an important public health priority, given the tendency of inactive behavior to track over time. Considering the high rates of physical inactivity at the beginning of adolescence, particularly among girls, and the evidence that physical activity during adolescence can predict future active or sedentary lifestyle, it is necessary to increase efforts and interventions to promote physical activity and health during childhood.

REFERENCES

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