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Heart rate monitoring is becoming increasingly popular among fitness enthusiasts, and for good reason. Whether it’s a rugged outdoor smartwatch or a discreet smart ring, smart wearable technology can help you understand whether you’re pushing yourself hard enough during exercise, how well you’ve rested at night, or whether you’ve been stressed out during the day, simply by listening to your heartbeat.
Some of the best fitness trackers even use machine learning to provide you with personalized workout recommendations based on how your health metrics change over time—not to mention that smart devices can be invaluable tools for endurance athletes. But how exactly do fitness trackers determine your heart rate? And how accurate are these measurements? We turned to the experts.
Most fitness watches and smart rings rely on a technology known as photoplethysmography (PPG). While its name may sound complicated, the technology is based on a fairly simple concept: the absorption of light by body tissue.
How does photoplethysmography work?
Dr. Peter Sogaard, a professor of cardiology at Aalborg University in Denmark and chief medical officer of VentriJect, the company behind the new cardiorespiratory fitness device, told Live Science via email that PPG uses optical sensors that determine heart rate by measuring changes in the volume of blood flowing through small vessels in the skin and underlying connective tissue.
With each heartbeat, the heart muscle contracts and relaxes, forcing new blood into the bloodstream. The contraction causes a temporary wave of increased blood volume and increased pressure on the artery walls, commonly called the systolic phase of the cardiac cycle. When the heart relaxes between beats, blood flow decreases, called the diastolic phase. PPG sensors detect these changes in blood volume and pulse pressure (the difference between systolic and diastolic pressures), then convert that data into a measurement of heart rate, Soegaard explained.
Fitness trackers measure heart rate by recording changes in blood volume, which is what we see when we check our pulse.
PPG sensors detect these changes in blood flow by emitting light at specific wavelengths into the skin. Components
Sourse: www.livescience.com
