Proskura, Patrycja, and Kazimierz Witkowski. “The Law on Sport in the Light of the Opinion of the Fitness Instructors and Personal Trainers”. Journal of Education, Health and Sport 7, no. 6 (June 25, 2017): 789–800. Accessed April 26, 2024. https://apcz.umk.pl/JEHS/article/view/4982.