In this paper of the Swiss Federal Institute of Sports in Magglingen, single ECG peaks where studied and analysed after the activity: https://pubmed.ncbi.nlm.nih.gov/31004219/ In this paper of the group of Dr. Desai from Cleveland Clinic in Ohio, a cardiologist stood next to the treadmill and studied and analysed every single ECG peak: https://journals.lww.com/acsm-msse/Fulltext/2017/08000/Variable_Accuracy_of_Wearable_Heart_Rate_Monitors.22.aspx In both …