“…For example, some authors defined physical activity as the practice of sports outside school as well as going to school by bike or walking 26,27 . Other authors considered any kind of vigorous and/or moderate physical activity, inside or outside school, in a structured way or not 28,29,30,31,32,33,34 . The lack of a homogeneous definition of physical activity is an important limitation for pooling, or even comparing, results among different studies.…”