Urtnowska, Katarzyna, et al. “Physiological Changes in the Locomotor System of a Pregnant and Related Lumbar-Sacral Pain - Examination of the Degree of Feeling Back Pain During Properly Running Pregnancy”. Journal of Education, Health and Sport, vol. 5, no. 7, July 2015, pp. 105-16, https://apcz.umk.pl/JEHS/article/view/2776.