Nowosielska-Swadzba, Danuta, Danuta Zwolinska, Marek Jendrysek, and Robert Podstawski. 2015. “Physical Activity As a Health Factor Modifying Heart Rate Variability (HRV)”. Pedagogics, Psychology, Medical-Biological Problems of Physical Training and Sports 19 (3):80-86. https://doi.org/10.15561/18189172.2015.0312.