In a paper of the Swiss Federal Institute of Sports Magglingen, it says, a simple chest strap such as the Polar H10 might be recommended as the gold standard for RR interval assessments if intense activities with strong body movements are investigated: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiKos3IhuH4AhWF_bsIHfGlD2kQFnoECAIQAQ&url=https%3A%2F%2Fwww.ppdb.ehsm.ch%2Finf2%2Frm%2Ff.php%3Ff%3D20200416162130_5e9869eab833b.pdf%26n%3DGilgenAmmann_RRIntervalSignalQuality_2019.pdf&usg=AOvVaw23MOAobT8so8HFGAdgdcPo This is might be true for intense activities with strong body movements, …