Dr. Evan Matthews is cardiovascular and exercise physiologist, Associate Professor, Exercise Science and Physical Education at Montclair State University near New York. https://www.sciencedirect.com/science/article/abs/pii/S1440244013001345 https://journals.humankinetics.com/view/journals/jpah/12/7/article-p976.xml https://scholar.google.com/scholar?hl=de&as_sdt=0%2C5&q=polar+t31+heart+rate+monitor&oq=polar+t31 https://scholar.google.com/citations?user=YHSEdWwAAAAJ&hl=en&citsig=AMstHGTc_RJkC5GTxrOLXv3dhnW1eMQaxg