Sociodemographic and behavioral factors associated with physical activity in Brazilian adolescents

The importance of physical activity for health has been demonstrated in various studies [1, 2]. During childhood and adolescence, the benefits offered by moderate-to-vigorous physical activity (MVPA) include lower cardiometabolic risk [3, 4], less fat mass [3, 5], and greater physical fitness (especially cardiorespiratory) [3]. In addition to these immediate results, physical activity in adolescence increases the probability of becoming an active and healthy adult [6] and lowers the risk of future health problems, such as fractures [7] and breast cancer [8]. Nevertheless, worldwide, fewer than 20% of adolescents aged 13 to 15 years practice physical activity at the recommended levels (more than 60 minutes of MVPA per day) [9].

Physical activity is determined by complex factors that vary widely between countries, and thus, it is important to research this topic [10]. Paradoxically, although 80% of the global population is located in low-and middle-income countries, only a small fraction of studies on the determinants of physical inactivity are conducted in these nations [10, 11].

In Brazil, physical activity among adolescents has been studied in school, during sports participation, during leisure time, and during active commuting [12‐14] However, few studies with representative data for the entire Brazilian population have investigated the role of socio-demographic and behavioral variables in determining the level of physical activity in adolescents [15]. The present study’s aims are as follows: 1) to describe the physical activity of Brazilian adolescents in various domains (physical education at school, during leisure time, and during active commuting) and 2) to investigate the socio-demographic and behavioral factors associated with physical activity.

More than two-thirds of the students studied resided in south-central Brazil (66.7%), and slightly more than one-fifth (22.4%) resided in state capitals. Most students were aged 14 to 15 years (63.9%), attended public school (82.8%), and self-identified as black or brown (55.6%). Less than one-sixth of the students (13.2%) reported working. Nearly half of the students (39.0%) were the children of mothers who did not complete elementary school. Slightly more than one-tenth of the students (12.5%) had mothers with higher education. Approximately two-thirds of the students came from families with at least one vehicle (63.8%). In the 30 days preceding the study, 5.1% of the adolescents smoked, 26.1% drank alcohol, and 2.4% used drugs. The mean nutritional score for the students was 42.50 (SE = 0.22) (Table 1).

Most of the students (97.0%) engaged in physical activity in at least one of the domains studied, especially physical education at school (81.7%) and leisure time physical activity (67.5%). The weekly frequency of all activities was greater among boys than among girls (Table 2). Only 29% reached the recommended level (> 300 min/week) of physical activity. Boys reached the recommended levels more often than girls (38.6% vs. 20%, respectively). Moreover, nearly two-thirds (61.8%) of students spent more than two hours per day engaging in sedentary behaviors; the prevalence of sedentary behaviors was similar between boys and girls (59.0 and 64.5%, respectively).

The results of the adjusted multiple regression models revealed the set of factors associated with each domain of physical activity. The prevalence of physical education at school was higher among the students who resided in capital municipalities, students aged 15 years or younger, white students, those who reported working, and those from a family with a vehicle (Table 3).

With regard to leisure time physical activity, the prevalence was greater among adolescents from the north region, those residing in rural municipalities, males, those younger than 13 years, those attending private schools, and those who reported having a vehicle in the household (Table 3).

The prevalence of active commuting was higher among students of yellow and brown race, those aged 15 years or younger, those who worked, those whose mothers had a secondary education (complete or incomplete), and those from families without a vehicle (Table 3).

Among the adolescents who reached the minimum recommended time for physical activity, the various domains contributed the following proportions to total physical activity: leisure time physical activity (PR 12.5; 95% CI 11.17-13.97), active commuting (PR 1.63; 95% CI 1.59-1.67), and physical education at school (PR 1.36; 95% CI 1.29-1.44).

Leisure time physical activity, active commuting, and LPA were associated with higher nutritional scores. However, physical education at school was associated with smoking at least once during the previous 30 days. Similarly, greater levels of physical activity were associated with the use of alcohol and drugs at least once during the previous 30 days (Table 4).

This study was the first Brazilian study to investigate the association between physical activity in various domains with socio-demographic and behavioral variables among adolescents using data from the nationally representative PeNSE 2012. The results of the present study indicate that only 29% of adolescents reach the recommended 300 minutes of physical activity per week, despite the high prevalence of physical activity. In 2009, the prevalence of physical activity in adolescents was 43, 1% (56, 2% in boys and 31, 3% in girls), however it is important to highlight that the coverage of the research and the physical activity questionnaire (commute and leisure time domains) has been changed for PeNSE 2012. In other Latin American countries such as Argentina, Chile and Venezuela around 10% of the adolescents are physically active (more than 60 min per day of moderate to vigorous physical activity), while in Uruguay, Peru, Ecuador, Colombia, Guyana and Suriname this proportion increases to 20% [9].

Brazil is a country with a continental dimension with a persisting social, cultural and economic heterogeneity. Programs and policies that promote physical activity should take into account differences between geographic locations. We found no difference for the prevalence of physical education at school among the regions in the adjusted models. As the country has a national policy for this matter, the differences verified (unadjusted) are possibly relate to the lack of infrastructure (such as sports goods and adequate physical space). This is probably the case in the North and Northeast regions (less developed regions of the country) and may by the case in the Southeast region (where the biggest share of the public schools are located, increasing the complexity of its administration). Leisure time physical activity was more prevalent in the North region, probably due to cultural factors and urban environments that allow (or promote) this domain of activity, situation less often verified in the regions South, Southeast and Midwest. However, accurately understanding such a phenomena becomes difficult facing rare/none publications in physical activity field concerning specifically the situation in each region and the lack of information about possible determinants of the disparities in PeNSE. Thus, studies, and even the surveillance system, designed specifically to understand the correlates/determinants of physical activity domains across the Brazilian regions are necessary”.

Additionally, students in rural municipalities participated in less physical education at school; however, these locations had a greater proportion of leisure time physical activity. Socioeconomic class is another aspect that should be considered. Higher education levels were associated with a greater probability of reaching the recommended levels of physical activity. A similar finding was reported by another study [27].

As in the other domains, there was less participation in physical education classes among older students, corroborating the results of prior studies [12, 28]. However, this age-related difference did not hold for meeting the recommended level of physical activity. The prevalence of physical education at school and active commuting was similar between the genders. Women are less involved in physical activity at all ages [12]. Therefore, proper planning of physical education at school and incentives for active commuting could be good strategies for getting women to reach the minimum recommended weekly levels of physical activity.

Despite high adherence among adolescents (82%), physical education at school only increased the probability of achieving the recommended levels by 36%. This finding can be explained by the low frequency and short duration of physical education classes. In Brazil, although law requires physical education classes, the minimum number of classes per week is not specified [29, 30]. They are generally offered twice a week and last 50 minutes, for a total of 100 minutes per week; this time is one-third of the recommended level for the age group. In addition, studies have shown that students are engaged in moderate-to-vigorous physical activity (objective measurements of MVPA) for only 20-47% of the physical education class time [31‐33]. Therefore, increasing the frequency and quality of physical education classes could improve the health of adolescents and promote activity in adulthood [34]. School is a suitable environment for developing active behavior: it is relatively safe, the required space and equipment are available, and appropriate professional guidance is offered. Therefore, school is a strategic location for reducing levels of physical inactivity in infants and adolescents. In addition, future studies could investigate environmental, sociocultural, and different physical education classes approach that are strongly related to a better adhesion to the practice in this domain.

Among the domains we studied, leisure time physical activity was the most important (PR 12.5; 95% CI 11.17-13.97) for achieving the recommended level of physical activity. This finding strongly suggests that adolescents who reach the recommended minimum of 300 minutes of physical activity per week do so more because of leisure time physical activity than because of physical education at school or active commuting. Leisure time physical activity is the main way that adolescents incorporate physical activity into their daily lives, reflecting the preferences of the study population. Therefore, strategies that promote physical activity by focusing on leisure time [35] could see better adherence rates, especially for groups of people who are just beginning to engage in physical activity (i.e., public school students, girls, and the children of mothers with little education). Studies have shown that interventions in public spaces, with easily accessible facilities and proper guidance, affect individual choices to engage in physical activity [10, 36‐38]. Providing appropriate public spaces lowers the physical, psychological, and financial barriers to leisure time physical activity [10, 37]. Conducting programs at plazas, parks, and beaches, or even along avenues or in places near homes, encourages greater participation by the population [36, 39]. For example, an ongoing community-base program, called Academia da Cidade, has showed to be an effective public health strategy to increase leisure-time physical activity in Brazilian urban settings (Recife) by providing PA classes in the community [40, 41]. In contrast, the perception of a lack of safety due to urban violence and dark areas could act as a significant barrier to engaging in physical activities in such spaces [42]. Additionally, Parra et al. study has suggested that this is a complex relationship once different environmental characteristics in Curitiba are associated with different physical activity outcomes [43].

Active commuting increased the probability of adolescents achieving the minimum recommended levels of physical activity by 63%. In total, 62% of the adolescents commuted at least one day per week, and 50% commuted five or more days per week. This type of physical activity was more common among students younger than 15 years, those whose mothers had secondary education, those who lived in a house without a vehicle, and adolescents who worked. A similar finding was reported in another study in which active commuting to school was associated with lower socioeconomic class [44]. Active commuting is an important domain for reaching the recommended levels of physical activity. Moreover, it is easy and inexpensive and does not require much additional time in the daily routine. Commuting is a good way to engage in physical activity without making large changes to the daily routine; however, the major modifiable barriers related to the city (the distance between the starting point and the destination, traffic-related hazards, and safety concerns) and the school (an appropriate and safe location for parking bicycles, locker rooms with showers) should be addressed in interventions to promote active commuting among adolescents [45].

Despite the association between physical activity and other health behaviors, we found that leisure time physical activity, active commuting, and LPA were associated with higher nutritional scores. However, physical education at school was associated with smoking at least once during the previous 30 days. Similarly, greater levels of physical activity were associated with the use of alcohol and drugs at least once during the previous 30 days (Table 4). Due to the small magnitude of the relationship, we strongly believe that residual confounding (such as the lack of more accurate information about economic status) might be the cause of this situation. As previously reported by some studies [10, 12], a clusterization of healthy behaviors was expected (as was one, complementary, for the unhealthy ones). An example of this includes the association between physical activity (leisure, commuting and total physical activity) and healthy diet score presented among our results.

The main limitation of this study was that physical activity was measured with a questionnaire and not with a direct method, such as an accelerometer. Although there is no agreement between continuous scores from questionnaires and those from accelerometers, the classification of participants into physical activity groups showed moderate to high agreement [27]. This agreement justifies the use of questionnaires for representative studies in large populations, such as the PeNSE. Additionally, a prior study that assessed students in the penultimate year of elementary school using a questionnaire and focus groups showed that the students were able to understand the questions and answers, were able to answer questions involving the selection of categories and frequencies, and left few questions blank [22]. The use of questionnaires was further supported by a validation study for the physical activity indicators used in the PeNSE, which indicated that the indicators performed well [46].

With regard to the completeness of the responses, most of the questionnaire items had response rates above 95%. Only the item about the mother’s education level had a higher (17%) non-response rate. Therefore, multiple imputation was used, and the expansion factors used for the analyses were recalculated considering the losses in coverage, which improved the results from multiple analyses. Imputation of missing data is always recommended because it considerably increases the reliability and power of the analyses [47].

With regard to external validity, the PeNSE involved a representative sample of Brazilian students from public and private schools. Brazil has a high coverage rate for elementary education: 88% of adolescents aged 15 to 19 years attend school [48]. Therefore, it is reasonable to assume that the same behaviors observed in the present study would be observed in the entire population of Brazilian adolescents.

In conclusion, we found that different physical activity domains are associated with specific socio-demographic and health behaviors. Physical education at school was higher among the students who resided in capital municipalities, students aged 15 years or younger, white students, those who reported working, and those from a family with a vehicle. Leisure time physical activity was greater among adolescents from the north region, those residing in rural municipalities, males, those younger than 13 years, those attending private schools, and those who reported having a vehicle in the household. Active commuting was higher among students of yellow and brown race, those aged 15 years or younger, those who worked and whose mothers had a secondary education, and those from families without a vehicle. In this sense, physical activity programs should take into account those specificities.

Physical activity is an important component of any health promotion program. It is still necessary to invest in policies that promote physical activity in all domains and to encourage interagency actions that focus on health, education, sports, the environment, safety, transportation, and social communication. Such actions will ensure that the population participates in determining the scope and design of these policies.