Partners, Personal Health Technology, Researchers, Workforce Health | By | 02/12/20

How Fitbit Trackers Monitor Heart Rate

I admit that I am slightly obsessed with monitoring my heart rate. I check my heart rate when I get up, during a spin class, yoga, a dog walk, traffic backups, and stressful meetings. A quick glance at my Fitbit and a few swipes immediately shows me my heart rate, plus lots more useful data. 

Having all this great information at my fingertips wasn’t always easy. My first experience with heart rate, maximum heart rate, and heart rate zones was at a cycling class at the YMCA. In not nearly enough time, an instructor explained the room’s new heart rate wall poster and what it meant. As a class, we fumbled through finding our pulse, counting beats, and multiplying by four to find our heart rate. For maximum heart rate, we subtracted our age from 220. Both are math problems I like to avoid—and I can with Fitbit. 

How Does Fitbit Detect My Heart Rate?

When your heart beats, your capillaries expand and contract based on blood volume changes. To determine your heart rate, the optical heart-rate sensor in your Fitbit device flashes its green LEDs hundreds of times per second and uses light-sensitive photodiodes to detect these volume changes in the capillaries above your wrist. Then your device calculates how many times your heart beats per minute (BPM). The optical heart-rate sensor detects a range of 30-220 BPM. 

Fitbit makes it so much easier than finding my pulse at my wrist or neck. On the Fitbit screen, I see my heart rate and other interesting information, specifically my heart rate zone and the time I’ve been in the zone. During an aerobic exercise class, I typically bounce around in different zones. On a dog walk, I’m more likely to stay in one zone for a longer period of time. 

Understanding Heart Rate Zones

Fitbit identifies three heart rate zones: Peak, cardio, and fat burn. These zones are based on your maximum heart rate.

  • Peak zone is where the most intense portion of your workouts happen, and you are at 80 to 100 percent of your maximum heart rate. I rarely reach this zone and when I do, I stay in it for 10 minutes or less. Most often I reach this zone in the latter half of a cycling class, when I’m pushing myself hard in a sprint challenge.
  • The cardio zone, which is 70 to 84 percent of your max heart rate, is where the hard work is done when you’re training for a big event. You can usually sustain it for about 30 minutes. I stay in this zone when I’m riding my bike to work. Not too fast, not too slow, steady training minutes. 
  •  In the fat burn zone, moderate workouts use 50 to 69 percent of your maximum heart rate. I find myself in this zone during a low-impact flow yoga class.

If there’s another heart rate zone that you want to track, you can create a custom zone on Fitbit. Find the “HR Zones” setting in your account profile and turn on “Custom Zone.” You can enter the upper and lower limits you want.

What Is Resting Heart Rate

Another important number to know is your resting heart rate. You can measure this after you’ve been sitting quietly for 30 minutes or when you wake up in the morning. Resting heart rate is the number of times your heart beats per minute when you are still and well-rested. This metric can be an important indicator of your fitness level and overall cardiovascular health. 

For adults, the typical resting heart-rate range is 60 to 100 beats per minute. Active people often have a lower resting heart rate. Drastic changes to this number can signify health issues and should be discussed with a doctor.

Fitbit estimates your heart rate based on your data from when you’re both awake and asleep to estimate your resting heart rate. To get the best results, wear your device to sleep. You can find more useful information on tracking your heart rate with Fitbit in this helpful FAQ.

Fitbit PurePulse Technology

Technology has vastly improved since the first time I learned about heart rate monitoring. Fitbit uses photoplethysmography in its PurePulse technology to track heart rate, which in turn can help you reach your weight goals, optimize exercise, and better manage stress levels. Here’s a quick glance at how this technology works.

Image source: Fitbit Know Your Heart with PurePulse

You can find more in-depth information about Fitbit heart rate technology here

Monitoring your heart rate and understanding the different zones is essential to helping you get the most from your Fitbit and reaching your health goals. 

And one final pro tip: try the Fitbit Relax App. Available on certain Fitbit devices, the app provides personalized deep breathing sessions (between 2-minutes or 5-minutes long) that can you find moments of calm throughout your day. Sixty-seven percent of people who use the Fitbit Relax App experienced a decrease in heart rate, according to Fitbit data.

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