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1. Introduction
It is now widely accepted that moderate-to-vigorous physical activity (MVPA) positively affects child and adolescent health [1]. In contrast, sedentariness is considered a potential risk factor in youth, as it is linked to the increased prevalence of overweight/obesity [2] and metabolic risk factors [1].
Although physical activity and sedentariness are sometimes viewed as opposite sides of the same coin [3], supporting the “displacement hypothesis” which assumes that inactive behaviours may replace more active ones [4,5], recent studies suggest that sedentariness is an independent construct from that of physical activity [4,6,7]. Studies have reported similar [2] and different correlates [8] of these two constructs, with distinct effect sizes and direction [7,9]. Further, these two behaviours can coexist [3], reinforcing the idea that the relationship between physical activity and sedentariness is far from being clear, with previous studies reporting conflicting results [4,9,10].
Both sedentariness and physical activity are linked with a wide array of biological, social, behavioural, and environmental correlates [2,8]. In this context, it has been suggested that sex [2], weight status [2], maturity [11], socioeconomic status (SES) [7,8], siblings’ influence [12], and sleep time [13] are related to time spent in these behaviours. Although schools are mainly viewed as delivering educational programs, taking into account the ecologic models of behaviours [14], the school environment may also provide opportunities for children to be physically active and to avoid extended sedentary periods through environments that may include playground areas, sports equipment and sporting facilities, recess periods, lunch breaks, and physical education classes [14,15,16]. Taken together, both child-level and school characteristics may explain a proportion of the variance in physical activity and sedentariness at the population level. Therefore, the aim of this study was to use a multivariate multilevel approach [17] to jointly analyse MVPA and sedentariness, investigating their relationship as well as their correlates in children within their school contexts.
2. Materials and Methods
2.1. Sample
The sample of the present study comes from the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE) [18].
A total of 777 Portuguese children, aged 9-11 years, from 23 schools from the North of Portugal, were enrolled in the ISCOLE project. In each school, after the project was approved by the physical education department, school principal and...