PLOS ONE | https://doi.org/10.1371/journal.pone.0204098 September 25, 2018 1 / 13 OPEN ACCESS Citation: Brustio PR, Moisè P, Marasso D, Alossa D, Miglio F, Mulasso A, et al. (2018) Participation in a school-based walking intervention changes the motivation to undertake physical activity in middleschool students. PLoS ONE 13(9): e0204098. Physical inactivity has become a global public health problem among children in developed countries [1], including Italy [2]. Indeed, physical inactivity and

more »

... e consequent increase in sedentary behavior among children and adolescents induces several health problems, including overweight and obesity [3], as well as decreased cardiovascular fitness [4] . Although a minimum of 60 min per day of moderate-to-vigorous physical activity is suggested, few children (i.e., approximately 40%) follow this recommendation [3, [5] [6] [7] [8] [9] . Moreover, the physical activity level tends to decrease over time from childhood to adolescence [9, 10] . Thus, the increase of daily physical activity to the recommended levels is important for children's health and wellbeing [7, 11] . Schools, particularly physical education classes, are a suitable place to promote all forms of physical activity [1, 12, 13] . Indeed, Italian physical activity action plans highlight the need to provide more opportunities to be active, particularly in childhood [14, 15] . For this reason, physical education programs are expected to promote an active and healthy lifestyle among children in schools [16] . However, the pressure due to grade testing, lack of time, and fear that the physical activity may negatively influence academic achievements are the most common barriers to physical activity in schools [17] [18] [19] [20] . Motivation is an important factor that contributes to physical activity participation [21, 22] . It is a dynamic process that incorporates cognitive, affective, and values-related variables, which are assumed to mediate the choice and attainment of achievement goals [23, 24] . The Self-Determination Theory (SDT) [25] is a framework for examining the relation between motivation and physical activity [26] . In particular, the SDT posits that the emphasis on internal and external forces fits with the presence of two types of motivation, namely intrinsic and extrinsic motivation [27, 28] . Although intrinsic and extrinsic motivations are on a continuum, the first type may concern the pleasure and satisfaction derived from participation, while the latter may refer to the engagement of activity to obtain some types of reward, to gain in status or to avoid punishment [27] [28] [29] . Autonomous forms of motivation (i.e., internal forms) are positively related to change, support [29] and long-term maintenance of physical activity [21] . On the contrary, controlled forms of motivation (i.e., external forms) can be characterized by greater levels of instability and usually do not promote long-term positive physical activity behaviors [21] . In children, a persistent motivation to physical activity includes internal forces, such as skill development challenge, excitement, and fun, as well as external forces with a high grade of stability, such as the demonstration of competence and affiliation [28, 30] . Similarly to physical activity, motivation to physical activity decreases with increasing age from childhood to adolescence [31] . However, a recent study [32] has reported that children with higher level of intrinsic motivation and enjoyment, as well as a greater decline in extrinsic motivation (e.g., social and competence goals), demonstrated higher levels of physical activity. Specifically, a higher level of intrinsic motivation was positively associated with physical activity level during physical education classes and physical leisure time [26] , as in non-educational context [8] . Brief active breaks during the school day are a relatively new and innovative method of increasing physical activity in educational settings [33] [34] [35] [36] [37] [38] [39] . These brief bouts of approximately 5-15 minutes can be considered to be an efficient and feasible intervention due to the short execution time and the relative low cost in a school context [33] [34] [35] 39] . Moreover, it does not require specific experience to be conducted in physical educational context. In particular, brisk walking activities in school context might positively affect physical activity level and the general health of the children [40] [41] [42] [43] . Due to the lower motor skills required Activity breaks and motivation PLOS ONE | https://doi.