## 1 Introduction  
Physical activity is described as the total amount of time spent engaged in daily life activities, work and school activities, recreational and sports activities, and other activities that increase the energy expenditure of the body [1]. Tracking the physical activity levels (PALs) is important research interest in public health, as having sufficient PALs is associated with higher health-related quality of life [2; 3; 4; 5]. Despite the conclusive evidence of the importance of physical activity at all ages, the problem is particularly important in youth, since the PALs in youth over the past few decades have significantly declined [6]. More specifically, 81% of the youth aged 11-17 years do not meet the recommended daily physical activity guideline of 60 minutes of moderate-to-vigorous physical activity [6; 7]. It is approximated that PALs in adolescents decline with age by a mean of -7% a year [8; 9]. Therefore, there is a global consensus of the importance of tracking the changes in the trends of PALs and related influential factors [10]. Numerous factors influence PALs, with the emphasis on biological, psychological, social, and environmental factors [11]. Over the last decade, interest has risen in the investigation of the factors that directly or indirectly influence PALs in children and youth [12; 13]. However, studies confirmed the importance of the living environment on lifestyle and consequently its influence on PAL [14; 15]. For example, an international study confirmed that adolescents who live only a few kilometers from urban centers have a significantly different lifestyle from their peers who live in urban communities [16]. This is indirectly confirmed in studies conducted with Italian, Polish, Austrian, Cyprus, Portuguese, Spanish, and Slovak children and adolescents [14; 17; 18; 19; 20; 21; 22]. Children and adolescents living in urban vs. rural communities regularly differ not only in PAL (with higher PALs in urban adolescents) but also in fitness status and anthropometric/body built indices [15; 21; 23; 24]. Although PALs are generally known to be influenced by certain personal (individual) characteristics (i.e., motivation, self-esteem, and conative facets), considering the established differences in PALs between rural and urban communities, it is expected that some specific factors associated with a community also determine the PALs among adolescents [22]. Indeed, the availability of equipment and public spaces for leisure activities (e.g., bike paths, squares, and courts), participation in the labor market, time spent outdoors, and perceived neighborhood safety, among other factors, were shown to be important determinants of PAL [15; 25]. Logically, adolescents from urban communities are more involved in organized sports activities, whereas those who live in rural communities are more engaged in unstructured outdoor physical activities (e.g., free play and walking) [19; 26]. Coronavirus disease 2019 (COVID-19), which was recognized in December 2019, was classified as a worldwide pandemic. The United Nations stated that the \"COVID-19 pandemic is the defining global health crisis of our time and the greatest challenge we have faced since World War II\". Due to detrimental health consequences, COVID-19 should be observed as a serious security threat. Most of the countries with confirmed cases of COVID-19 infections imposed certain measures of social distancing, including lockdowns [27; 28]. In addition to other measures of social distancing (e.g., the closing of shopping centers, schools, universities, and places of worship), lockdown measures included the closing of sports facilities (e.g., gyms, recreational centers, and sport-clubs) [29]. Therefore, a significant reduction in PAL was expected [30]. The claims about a decline of PALs as a result of the COVID-19 pandemic were indirectly proven by the globally popular Fitbit company, which produces activity tracking devices (Fitbit, Inc., San Francisco, CA), where data from more than 30 million users were collected.