Коновалов [V. Konovalov] В. В., Касьян [A. Kas’an] А. В., and Череднiченко [A. Cherednichenko] А. В. “Optimal Physical Activity of Students in the Initial Period of Training”. Slobozhanskyi Herald of Science and Sport, no. 3(36), June 2013, pp. 16-19, https://journals.uran.ua/index.php/1991-0177/article/view/20457.