Sikora , Jan, and Agnieszka Wartecka-Ważyńska. “The Economic and Social Conditions of the Physical Activity of People Who Are 50+ in the Light of Research”. Studia Oeconomica Posnaniensia, vol. 6, no. 10, Oct. 2018, pp. 121-36, https://doi.org/10.18559/SOEP.2018.10.8.