When myocardial cells are at rest, there is a potential difference formed by the concentration difference of positive and negative ions on both sides of myocardial cell membrane. With the beating of the heart, the potential difference of myocardial cells quickly becomes zero. This process is called depolarization, during which a slight voltage change occurs.
The principle of optical heart rate is called "Photoplethysmography (PPG)", which is a technique to measure pulse optically.
brief introduction
To put it simply-the electrode pads located on both sides of the chest band (heart rate band) will be responsible for capturing the tiny electrical changes on the skin surface caused by the beating of the heart, and these tiny changes will be sent to the heart rate meter to be converted into the heart rate we see at present.
The blood flow in the artery will also change periodically with the contraction and relaxation of the heart. When contracting, heme has a high density and will absorb more green light; During diastole, the density of heme is low, and it reflects more green light.
Baidu encyclopedia-heart rate table