Introduction

The health benefits of moderate-to-vigorous physical activity (MVPA), especially among youth, are well known^{1, 2}. It is also acknowledged that, around the world, the urbanization process affects children and adolescents’ daily lives in many different ways^3-5. Further, this impact is more evident in developing countries, causing drastic changes in lifestyles⁶, leading to decreasing levels in habitual physical activity (PA), increasing levels in sedentariness⁶, and as a consequence, an escalation in the prevalence of overweight and obesity^{7, 8}.

Despite both developed and developing countries being affected by the urbanization process, they are in different stages of this process⁹. Developed nations are in the so-called “last stage” of nutritional transition⁹, with a high prevalence of sedentariness and obesity, but with people becoming more aware of the benefits of balanced diets and physically active lifestyles, and that changing diets and PA habits will, in all likelihood, prevent or delay co-morbidities related to physical inactivity and obesity. Developing nations, such as Sub-Saharan countries are, in general, in the fourth stage of this transition⁹, characterized by people becoming more affluent with the adoption of a westernized way of life, with the expected increments of overweight/obesity prevalence and a more sedentary daily life. As a consequence, there is a trend in developing nations for high prevalence of sedentariness and a relevant decrease in MVPA levels, namely among youth, with similar frequencies of those found in developed nations^{10, 11}.

PA differences in European countries have been systematically studied. For example, Aibar, Bois, Generelo, Zaragoza Casterad, Paillard¹² reported that Spanish adolescents were more physically active than French adolescents; in addition they reported that only 35.9% of adolescents complied with current PA guidelines (60 min/day of MVPA). Further, Ramirez-Rico, Hilland, Foweather, Fernandez-Garcia, Fairclough¹³ reported that English adolescents were less sedentary and more active than their Spanish peers, and the percentage of adolescents achieving the recommended MVPA levels was about 25% overall.

To our knowledge, few studies have investigated differences in PA among children from countries with diverse socio-economic characteristics. In a recent review of worldwide variation in PA levels of adolescents from 105 countries, Hallal et al.¹⁰ reported that more than 80% of youth do not achieve the recommended daily MVPA levels; further, this prevalence tended to be lower in developing nations. In the African context, Peltzer¹⁴ reported that only 14.2% of children from 8 countries were physically active (5 days or more in a week with at least 60 min·day^-1); additionally there are large differences among countries meeting the PA guidelines, 17.7% in Uganda and 9.0% in Zambia.

Portugal and Mozambique are countries with different social, economic and cultural characteristics. A previous study conducted in 2009 comparing PA levels in 6- to 16-year-old school-age children and adolescents from these two countries¹⁵ reported that rural Mozambican youth engaged in significantly higher PA levels than their Portuguese peers. However, due the urbanization process that has affected the lifestyles of youth from these two countries, this scenario could not be seen in a more recent study^{16, 17}. Recent data have shown that the proportion of Portuguese children aged 10-11 years complying with the recommendation of at least 60 min·day^-1 of MVPA is 36% (51.6% for boys, 22.5% for girls), and that this prevalence decreases with age, with only 4% (7.9% of boys, 1.2% of girls) of adolescents aged 16-17 years attaining the recommended MVPA guidelines¹⁷. Although there is no nationally representative data for PA in Mozambican youth, there is some evidence of a decline during the last decades^{15, 16}. Given that the urbanization process may be contributing to a decrease in children and adolescent’s PA levels, the purpose of this study was to analyse the effects of age, sex, BMI and country of origin (Mozambique versus Portugal) on levels of PA and sedentariness in youth. Hence, we hypothesize the presence of significant associations of these covariates in youth PA levels and sedentariness in both countries.

Methods

Results

Descriptive statistics for BMI, PA and ST are shown in Table 1. On average, Portuguese and Mozambican boys and girls failed to achieve the 60 min·day^-1 recommended MVPA levels. Except for MVPA, significant differences were found for LPA and ST - Mozambican children and adolescents have, on average, more LPA and ST; further, Portuguese youth have higher BMI values.

Figure 1 presents graphical representation of the mean values ​​of BMI, PA and ST, adjusted for age and WTA (except for BMI that was only adjusted for age). After adjustments, BMI differences remained, but no statistically significant differences were observed for LPA and ST between countries; on the other hand, MVPA differences became significant for boys and for the total sample.

BMI: Body mass index; MVPA: moderate-to-vigorous physical activity; LPA: Light physical activity; ST: Sedentary time; PT: Portugal; MZ: Mozambique.

Figure 1: Graphical representation of means±standard errors for BMI, PA and ST after adjustment for age and WTA, by country. 

A very low frequency of children and adolescents, from both countries, complied with the recommended MVPA daily levels - only 4.3% in Mozambique and 3.9% in Portugal. Additionally, a moderate to high frequency of children were classified as being overweight/obese: 18.2% in Mozambique and 32.5% in Portugal.

Multiple regression analysis results are presented on Table 3. Mozambican children (β=-5.743, p=0.001), girls (β=11.700, p<0.001) and those with high BMI (β=-0.989, p<0.001) spend, on average, less time in MVPA. Similarly, girls (β=17.027, p=0.009 for LPA; β=-28.725, p<0.001 for ST), older youth (β=-27.083, p<0.001 for LPA; β=26.927, p<0.001 for ST), and those with higher BMI (β=-2.989, p=0.001 for LPA; β=3.978, p<0.001 for ST) spend less time in LPA, but have more ST; country of origin did not have a significant effect on LPA or ST. WTA was positively correlated with the three phenotypes, meaning that children who used the accelerometer for more time tend to report more time spent in PA and sedentariness.

Discussion

In this paper we found differences in LPA and ST between countries, where Mozambican youth (especially boys) spent more time in these behaviours when compared with their Portuguese peers. Differences in PA between children and adolescents from many nationalities have been reported by Aibar, Bois, Generelo, Zaragoza Casterad, Paillard¹², Ramirez-Rico, Hilland, Foweather, Fernandez-Garcia, Fairclough¹³, and Verloigne et al.²⁸, showing differences not only in distinct PA expressions, but also in sedentariness (both determined by accelerometer). Similarly, using questionnaire data from 8 African countries, Peltzer¹⁴ reported differences in school-children and adolescents’ PA. These results highlight the potential of social, cultural and environmental correlates on youth behaviour, namely their PA^{29, 30}.

Cross-cultural studies contrasting youth PA differences from countries with diverse socio-economic characteristics are scarce. Additionally, if available they frequently report PA levels or sedentariness by country or region, aiming to explore the worldwide patterns in these behaviours^{10, 31}. A previous study ¹⁵ compared PA levels (assessed by accelerometry) between rural Mozambican and urban Portuguese youth, and reported that Mozambicans had significantly higher total PA, showed less PA decline with age, but engaged in fewer minutes at high intensity PA than their Portuguese peers. The results for MVPA from the present study are somewhat similar to these previous results, with Mozambican boys and girls having lower MVPA than their Portuguese peers; however, significant mean differences were observed in LPA or ST. These results can be explained in different ways. Firstly, in the last decades, Mozambique passed through a social and economic transition period, with changes in lifestyle with visible consequences in youth PA and sedentariness, especially those from urban/suburban areas¹⁶. As such, children and adolescents are more sedentary and spend less time in activities of moderate and high intensity, and this can be a possible explanation for the lower time spent in MVPA found among Mozambican youth as compared to Portuguese.

In general terms, youth from both countries do not comply, on average, with recommended MVPA levels (60 min·d^-1). This low mean value reflects the percentage of children attaining the recommended MVPA guidelines: 8.3% and 7.7% in Mozambican and Portuguese boys, respectively, and only 1.3% and 1.5% in Mozambican and Portuguese girls, respectively. Although these are very low values, and of great concern, they are in accordance with the current worldwide trend which is characterized by low PA levels, in association with high ST¹⁰. For example, European youth data showed that only 4.6% of girls, and 16.8% of boys, aged 10-12 years, from 5 countries, reached the daily MVPA guidelines²⁸. In the African context, Muthuri, Wachira, Onywera, Tremblay³² reported that among 9-11 years old Kenyan children, only 12.6% met the MVPA recommendations, while Peltzer¹⁴ concluded that, among adolescents from eight African countries (Botswana, Kenya, Namibia, Senegal, Swaziland, Uganda, Zambia, Zimbabwe), only 14.2% spend at least 60 min·d^-1 in MVPA on 5 or more days per week.

Results of the multiple regression analysis showed significant effects of sex, age, BMI, WTA and country on PA and sedentariness. There are consistent lines of evidence showing sex and age differences in PA, where girls and older children and adolescents tend to be less active and more sedentary^33-35. Our results reinforce this trend, since girls spend less time in MVPA and LPA, as well as more time in sedentary activities; older adolescents are less engaged in LPA but are more sedentary than their younger counterparts. There is evidence that BMI is inversely associated with PA and positively associated with sedentariness^36-38. Among Mozambican and Portuguese adolescents, higher BMI was associated with lower MVPA and LPA, but also with higher time spent in sedentary behaviour. This result is of concern because of the observed increases in the prevalence of overweight/obesity in young population groups during the last decades^{7, 8}. In addition, children with more WTA had more MVPA, LPA and ST as expected, since the higher the amount of time recorded by the accelerometer, the higher the time spent in different PA phenotypes and sedentary activities will be registered.

The last PA and sedentariness predictor was country of origin, and the results showed that Mozambicans tend to spend significantly less time in MVPA. It is possible that this result is related to lifestyle changes observed in Mozambique during the last decades, mostly due to the urbanization process, which lead to a decrease in leisure time activities linked with increments in electronic entertainment media use among youth as previously suggested^{39, 40}; as a result, children became less active and more sedentary¹⁶; however, because we do not have any objective information regarding this issue, we can only speculate about this possible association. In addition, there seems to exist a trend among African children and adolescents to be engaged in greater amounts of LPA as compared to MVPA^{15, 32, 41}, although there were no differences in LPA observed in this study. On the other hand, a greater involvement of Portuguese children and adolescents in sports may also explain these results, since their sports practice gives them opportunities for engagement in more energy-demanding activities¹⁵.

This study is not without limitations. Firstly, it was not considered a proportional sample in each country. Furthermore, the present study did not intend to have representative samples from each city, nor from each country, as it is similar to other well-known studies^{42, 43}. Secondly, we do not have information regarding the context of the PA and sedentariness (we only focused on objectively determined overall MVPA, LPA and ST), which could provide a better understanding of the cross-country differences. Thirdly, although cut-off points advocated by Treuth et al.²⁷ are internationally accepted, they tend to produce lower estimates of PA than other published cut-points, which can partly explain the low percentage of children complying with the recommended 60 minutes of daily MVPA. Fourthly, we did not adjust PA or ST for biological maturation because a large number of subjects did not have information in sitting height (about 20% of the sample). Yet, as suggested by Sherar, Cumming, Eisenmann, Baxter-Jones, Malinal⁴⁴, the association between biological maturity and PA is rather inconsistent.

This study also has several strengths. Firstly, the use of an objective method (accelerometer) to measure PA and ST is a marked strength. Secondly, the use of the same accelerometer protocol in both countries ensures a high degree of robustness in the data. Thirdly, the use of samples from very different countries in socio-economic and cultural terms provides a unique opportunity to study correlates of PA and sedentary behaviour.

Conclusions

In summary, the present study found cross-country differences in MVPA between Mozambican and Portuguese youth. In addition, in both countries, a low percentage of children complied with the recommended daily MVPA levels. In general, girls, older children and those with higher BMI tend to spend less time in MVPA and LPA and more time being sedentary. Mozambicans are less involved in MVPA than Portuguese. Since low levels of MVPA in early life are related to obesity and its comorbidities in adulthood (i.e., they track over time), promoting strategies and programs to enhance active living styles during this period should be primary public health and education targets.