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1. Introduction
Socio-economic status (SES) has been well described as an important determinant of physical activity and sedentary behaviour, however, these associations are not consistent across the literature, particularly in adolescents [1]. We have previously shown in a sample of rural South African adolescents that SES at the maternal, household, and community levels independently predicted time spent in sedentary behaviours, as well as time spent participating in school and club moderate to vigorous intensity physical activities [2]. Further, the association between SES and body mass index (BMI) differs between high-income and low- or middle-income countries, with studies from high income countries reporting an inverse association between SES and obesity [3,4] and studies from many sub-Saharan African countries showing a positive association between SES and obesity [5,6,7,8]. National data from South Africa has shown that this association may not be linear [9], and may be influenced by different physical activity patterns across communities, as well as other factors, such as food security and access to nutrition.
Results from the 2016 Healthy Active Kids South Africa (HAKSA) report card [10] have shown that although more than 50% of South African children and adolescents are meeting physical activity recommendations, physical activity participation is lower in girls than boys, and decreases with age. Active travel is still a significant contributor to daily physical activity in South African children and adolescents, and has recently been shown to be high in rural adolescents [2] in whom the prevalence of overweight and obesity is also increasing [11]. Dugas et al. [12] have recently shown in each of their study sites from five low-and middle-income countries, including South Africa, that there was a significantly greater increase in body weight over a two year period in participants meeting physical activity guidelines compared to those who did not meet the guidelines. This suggests that the traditionally-accepted inverse association between physical activity and BMI may be confounded by changing food environments in transitioning societies, and that other factors may play a more significant role in determining BMI and body composition. Time spent in sedentary behaviours has also been shown to be high in some South African populations [13,14], but whether this predicts adiposity in the context of socio-demographic factors in urban and rural populations remains to...