Groffik, D., K. Frömel, M. Witek-Chabińska, R. Szyja, R. Žatka, and B. Urbański. “Daily and School Physical Activity of 16 Year-Old Girls and Boys”. Health Promotion & Physical Activity, vol. 4, no. 3, Jan. 2019, pp. 12-19, doi:10.5604/01.3001.0012.8669.