How Does a Smart Watch Measure Your Heart Rate?
As technology continues to advance, it’s becoming easier and easier to track your own heart rate. As one of the most important organs of your body, the heart can be a critical tool to monitor your overall health.
While the old fashioned method of counting your heartbeat on a pressure point still proves reliable, technology has made it much easier and more convenient to track your heart rate with a smartwatch.
Why is Measuring Your Heart Rate Important?
When it comes to your heart rate, think about it like you’re running a marathon. You don’t want your pace to be too slow, too fast, or too irregular. A good steady pace is what gets you to the finish line – in your heart’s case, a long, healthy life.
So what is a good, steady heart rate?
Between 60 to 100 beats per minute (bpm) is considered a normal heart beat. A heart rate that consistently falls below 60 bpm is considered a slow heart rate or bradycardia. According to the American Heart Association, complications associated with this condition can include: heart failure, frequent fainting, and, in extreme cases, cardiac arrest (1).
Conversely, a heart rate that consistently beats above 100 bpm is considered a fast heart rate and referred to as tachycardia. If left untreated, this condition could lead to blood clots, strokes, or cardiac arrest.
While both of these conditions can be treated with medication, surgery, or a pacemaker, you may not even be aware of the issue unless you monitor your heart rate. Regular visits to the doctor are essential for maintaining a healthy lifestyle, but wearing a smartwatch can help you monitor your heart rate on a daily basis.
How Do Smart Watches Measure Your Heart Rate?
Smartwatches have become increasingly popular in the past few years as the advancing technology can be beneficial to monitoring your health, performance, sleep, and more.
According to Pew Research Center, one in five Americans wear a smartwatch or fitness tracker, and according to Statista, 59% of people use their smartwatches to monitor their heart rate (2,3).
Even when you’re not thinking about it, a smartwatch is constantly reading your heart rate and, depending on the watch, may even alert you of an irregularity.
But how does it work?
You may have noticed the glowing green light on the back of your smartwatch. According to the Royal Society of Chemistry, smartwatches use green LED lights because your blood absorbs green light (4). This phenomenon is called spectroscopy, or the study of absorption and emission of light.
Smartwatches are equipped with sensors and these LED lights that use non-invasive photoplethysmography (PPG) technology to measure the changes in your blood flow (5). As your heart beats faster, your blood vessels expand, which helps increase blood flow. Your smartwatch is able to count how many times your heart beats per minute, which determines your heart rate.
How Accurate Are Smart Watches?
While visiting your doctor is essential for keeping up with your health and diagnosing any serious conditions, your smartwatch can be a quick and convenient way to track your heart rate.
But can you trust the device on your wrist?
A study conducted by the Heart Rhythm Society suggests that you can (6). In the study, patients wore one of the following watches: the Apple Watch Series 2, Samsung Galaxy Gear S3 and the Fitbit Charge 2.
The accuracy during the testers resting heart rate within five beats per minutes was 100%, and the accuracy during paroxysmal palpitations within 10 beats per minute was also 100%.
This shows that smartwatches can be a reliable and easy way to keep track of your heart rate.
Tips on Getting the Most Accurate Reading
If you’re having a difficult time getting an accurate reading of your heart rate on your smartwatch, try these tips and tricks for optimal heart rate readings.
Where You Wear it Matters
When it comes to measuring your heart rate, where you wear your watch matters. Your watch reads your blood flow, so the softer the tissue it’s positioned on, the more accurate reading you can get. It’s recommended to wear your watch two fingers above your wrist joint, and if you have tattoos, try to avoid wearing it on that area.
How You Wear it Matters
You may have a tendency to wear your watch too loose or too tight, but the right amount of tightness is key. You should wear your watch tight enough so no light can shine through to disrupt the sensor, but not tight enough to cut off circulation.
Start it Before Your Workout
Just like your body, your watch needs some time to “warm up” before jumping right into sports mode. In order to get a stable measurement, start your workout on your watch before your workout. A good time to start it is when you’re walking into the gym or starting your warmup.
Keep the Sensor Clean
Dirt and scratches on your watch’s sensor can result in a less accurate heart rate reading. That’s why it’s important to keep your watch clean and handle it with care to help avoid any damage. You can use a damp cloth to wipe off the sensor.
Keep it Updated
While it may not seem that a simple update could help read your heart rate better, it actually can. Smartwatch companies are constantly improving and updating their software, so it’s important to keep your watch up to date for optimal effectiveness.
Sources:
American Heart Association. (2024, Sept. 24). Bradycardia: Slow Heart Rate. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/bradycardia--slow-heart-rate
Vogels, Emily A. (2020, Jan. 9). About one-in-five Americans use a smart watch or fitness tracker. https://www.pewresearch.org/short-reads/2020/01/09/about-one-in-five-americans-use-a-smart-watch-or-fitness-tracker/
Statista. (August 2022). Which of the following health metrics do you use your smartwatch/fitness tracker to monitor? https://www.statista.com/statistics/1326249/health-metrics-tracked-by-wearables-in-the-us/
O'Donoghue, John. (2021, January 18). I ‘heart’ my smartwatch. https://edu.rsc.org/feature/the-science-of-smartwatches/4013008.article
Allen, John. Photoplethysmography and its application in clinical physiological measurement. Physiological Measurement 2007; 28(3). doi: 10.1088/0967-3334/28/3/R01
Heart Rhythm Society. (2018). New Study Show Popular Smart Watches Accurately Measure Rapid Heart Beat. https://www.hrsonline.org/news/press-releases/new-study-show-popular-smart-watches-accurately-measure-rapid-heart-beat