Heart rate variability: Know about biometric most fitness trackers measure

This kind of wearable device uses green light to detect blood flow beneath your skin and deduces your heart rate

Your heart beats around 100,000 times every day. Heart rate is a key marker of cardiovascular activity and an important vital sign. But your pulse is not as steady as a precision clock – nor would you want it to be.

As a cardiovascular physiologist, I measure heart rate in nearly every experiment my students and I perform. Sometimes we use an electrocardiogram, such as you’d see in a medical clinic, which uses sticky electrodes to measure electrical signals between two points of your body. Other times we use