What Is BPM in smartwatches, and why should you care?

Smartwatches have transformed themselves from being smart timekeeping devices to personal health companions. Today, most smartwatches are designed as health-centric wearables with the ability to track various health metrics of the wearer. One feature that stands out is heart rate monitoring, which displays heart rate in real-time to display the result in BPM or beats per minute.

Here’s a look at what is the meaning of BPM in a smartwatch, how a smartwatch measures heart rate in BPM, and why real-time heart rate monitoring is important.

What is BPM in a smartwatch?

BPM is the unit used to measure heart rate and it stands for beats per minute. In a smartwatch, it represents the number of times your heart beats in 60 seconds. With its ability to measure heart rate, a smartwatch acts as a personal monitoring device that allows users to measure and display heart rate in real-time on their wrist. The data can offer valuable insights into the health of your heart.

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While factors such as age, fitness and stress level can influence the heart rate, it also varies depending on your activity. Your body can automatically control your heartbeat to match your activity with your heartbeat getting faster when you are active and dropping when you are resting.

A normal resting heart rate for adults ranges from 60 to 90 beats per minute, and a lower heart rate at rest implies more efficient heart function and better cardiovascular function. A well-trained athlete tends to have a normal resting heart rate closer to 40 beats per minute.

How does a smartwatch measure heart rate in BPM?

A modern smartwatch with a heart rate monitor commonly uses one of two methods to record heart signals: ECG and PPG. 

ECG or Electrocardiography, where sensors measure the bio-potential generated by electrical signals controlling the expansion and contraction of heart chambers. An ECG is the preferred method of heart rate monitoring in medical devices but can be found in very few smartwatches like the Apple Watch Series 9 and Samsung Galaxy Watch6.

Most smartwatches in the market use PPG (Photoplethysmography) to measure heart rate. The PPG sensors (the green LEDs on the back of the watch) use a light-based technology to measure the blood volume controlled by the heart’s pumping action. These are optical sensors shining light from an LED through the skin, and the light refracting back is translated into heart rate data.

How to measure your heart rate in BPM on a smartwatch?

Before we tell you how to measure your heart rate using a smartwatch, the important factor for quality reading is fit. It is recommended that you wear the smartwatch about one finger length below your wrist bone. You should also wipe the sensor array clean and ensure good contact between the sensor array and your skin. Here’s how to measure your heart rate on a smartwatch:

Step 1: Place the smartwatch on your wrist and tighten the strap

Step 2: Open the heart rate monitoring app or ECG app on your smartwatch

Step 3: Wait for the LED lights to send a signal and for the device to measure your heart rate

Step 4: The heart rate will be displayed in BPM on the screen

Heart rate monitoring in smartwatch: Importance and accuracy

The evolution of smartwatches from glorified pedometers to health monitoring devices is an accomplishment in its own right. Even though they have added features like SpO2 measurement and blood pressure monitoring, their ability to track heart rate continues to be the key feature.

There are several stories of people saying their smartwatch saved their lives thanks to early indications of abnormal heart rate. Modern smartwatches use heart rate monitoring to help you with the early detection of irregular heart rhythms, track your cardiovascular fitness, provide insights into stress levels, and in the case of athletes, help them train in heart rate zones.

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Despite all these benefits, a smartwatch’s ability to measure heart rate should not be seen as a medical device equivalent. They are capable of alerting you ahead of time but that does not make them capable of diagnosing any sort of health condition.

A 2021 study by NIH found that optical heart rate sensors in commercial wearables or smartwatches did not work well on people with darker skin or obesity. The wrist is also not the ideal place for these sensors as your arm movement can lead to noise, and not every algorithm can effectively filter it out.

In a nutshell, a smartwatch can be an excellent entry point into understanding your heart and health in general. While the sensors powering these devices have gotten better over the years, the medical community is still on the fence about the accuracy of the data collected by these devices.