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What should I know about my heart rate data?

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This article provides everything you need to know about using your heart rate tracker effectively.

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How does my tracker detect my heart rate?

When your heart beats, your capillaries expand and contract based on blood volume changes. PurePulse LED lights on your tracker reflect onto the skin to detect blood volume changes and finely tuned algorithms are applied to measure heart rate automatically and continuously. The heart rate icon you see on the display tells you if you're in one of three heart rate zones.

What are heart rate zones?

Heart rate zones can help you optimize your workout by targeting different training intensities. The default zones are calculated using your estimated maximum heart rate. Fitbit calculates your maximum heart rate with the common formula of 220 minus your age. The illustrations below provide examples for each zone. Note that the appearance of the icons may look slightly different between trackers; for example, dots instead of dashes. For more information about zones, see the American Heart Association's Target Heart Rates article.

Peak zone

Peak zone, which means your heart rate is greater than 85% of maximum, is the high-intensity exercise zone. The peak zone is for short intense sessions that improve performance and speed.

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Cardio zone

Cardio zone, which means your heart rate is 70 to 84% of maximum, is the medium-to-high intensity exercise zone. In this zone, you're pushing yourself but not straining. For most people, this is the exercise zone to target.

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Fat Burn zone

Fat burn zone, which means your heart rate is 50 to 69% of maximum, is the low-to-medium intensity exercise zone and may be a good place to start for those new to exercise. It’s called the fat burn zone because a higher percentage of calories are burned from fat, but the total calorie burn rate is lower.

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Out of zone

When you’re out of zone, which means your heart rate is below 50% of maximum, your heart rate may still be elevated but not enough to be considered exercise.

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Custom zone

Instead of using the three default zones you can create a custom zone if you're targeting a specific heart rate. From the Fitbit app dashboard, tap or click the Account icon (User-added image) and find Heart Rate Zones. Then enter your custom zone.

On fitbit.com, log into your dashboard and click the gear icon in the upper right. Choose Settings > Personal Info. There you can enter your custom zone.

What is resting heart rate?

Resting heart rate measures your heart beats when you are still, and it can be an important indicator of the health of your heart. According to the American Heart Association website, “the average resting heart rate is 60-80 beats per minute, but it’s usually lower for physically fit people.” This is because, “active people often have lower heart rates because their heart muscle is in better condition and doesn’t need to work as hard.” Also, the average resting heart rate rises with age. For more information, see the American Heart Association's All About Heart Rate article.

How is resting heart rate measured?

Resting heart rate refers to the heart rate measured when you’re awake, calm, comfortable, and have not recently exerted yourself. We use your heart rate data from when you’re awake and asleep to estimate your resting heart rate. For best accuracy, wear your tracker to sleep. 

Your resting heart rate is usually higher than your heart rate while you are asleep, so don’t be surprised if your resting heart rate is higher than the lowest number that you see in your heart rate graphs.

What is max heart rate?

Max heart rate is used to calculate different heart rate zones. Fitbit calculates your max heart rate with the common formula of 220 minus your age. Don't be concerned if occasionally during intense exercise your heart rate goes above your Fitbit-calculated max heart rate.

Instead of using the default, you can create a custom max heart rate if you're targeting a specific heart rate. In the Fitbit app dashboard tap or click Account and find an option to change your heart rate zones. From there you can create a custom max heart rate.

What impacts the accuracy of my heart rate reading?

As with all heart-rate tracking technology, whether a chest strap or a wrist-based sensor, accuracy is affected by personal physiology, location of wear, and type of movement.

For all-day wear when you’re not exercising, your tracker should usually rest a finger’s width below your wrist bone and lay flat, just as you would wear a watch. Fitbit’s PurePulse heart rate tracking system is designed to be most accurate when the tracker is worn on the top of your wrist.
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For improved heart rate accuracy keep these tips in mind:
  1. Experiment with wearing the tracker higher on your wrist during exercise. Because blood flow in your arm increases the farther up you go, moving the tracker up a couple inches can improve the heart rate signal. Also, many exercises such as push-ups cause you to bend your wrist frequently, which is more likely to interfere with the heart rate signal if the tracker is lower on your wrist.
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  2. Do not wear your tracker too tight; a tight band restricts blood flow, potentially affecting the heart rate signal. That being said, the tracker should also be slightly tighter (snug but not constricting) during exercise than during all-day wear.
  3. With high-intensity interval training, P90X, boxing, or other activities where your wrist is moving vigorously and non-rhythmically, the movement may prevent the sensor from finding an accurate heart rate. Similarly, with exercises such as weight lifting or rowing, your wrist muscles may flex in such a way that the band tightens and loosens during exercise. Try relaxing your wrist and staying still briefly (about 10 seconds), after which you should see an accurate heart rate reading. Note that your tracker will still provide accurate calorie burn readings during these types of exercise by analyzing your heart rate trends over the course of the workout.

Note that if you remove your tracker but it keeps moving, for example if you put it in a pocket or backpack, the tracker may display an erroneous heart rate reading. To prevent this by turning off heart rate tracking when the tracker is not in use, log into your dashboard and go to Settings > Devices to turn your Heart Rate Tracking to "Off."

What impacts my heart rate?

Your heart rate may be affected by any a number of factors at any given moment. Movement, temperature, humidity, stress level, physical body position, caffeine intake, and medication use are just a few things that can affect your heart rate. Different medical conditions and medications can impact your heart rate. Consult your doctor before starting an exercise routine.

What is my cardio fitness score?

Your cardio fitness score, Fitbit's estimate of your VO2 Max, is an indicator of overall fitness that can help predict performance for endurance-based activities including running, biking, and swimming (source). At this time it is only available with Fitbit Blaze and Fitbit Charge 2. For more information, see What is my cardio fitness score

How do I change the heart rate setting on my tracker?

Log into your fitbit.com dashboard and click the gear icon in the top right corner. Under Settings > Devices > Heart Rate, you can choose On, Auto, or Off.

The default setting of Auto is appropriate for most people; the heart rate tracker  is active when you are wearing it and is inactive when you remove it. If there are times when your heart rate isn’t being tracked even though you are wearing your tracker, you can choose On. If you aren’t interested in heart rate tracking or want to maximize battery life, you can choose Off.

What is PurePulse?

Our PurePulse heart rate tracking is the only heart rate technology to offer automatic, continuous wrist based tracking for all-day health insights and workout intensity. It is uniquely designed to measure heart rate all day, with always-on optical heart rate sensors that still maintain extended battery life. PurePulse allows you to accurately track workout intensity and calorie burn with finely tuned algorithms that provide insight through interactive charts and graphs.

What activities don't work with PurePulse?

Activities with extreme arm motions, such as boxing, are harder to track second to second; however, PurePulse can still provide accurate calorie burn readings during these types of exercises by analyzing your heart rate trends over the course of the workout.

Are the PurePulse LEDs safe?

Allergy to visible light is extremely rare and the PurePulse LED lights are on the visible spectrum, similar to the lights in your home or office. The LED lights have very low power so they won't burn your skin, and they're programmed to shut down if your device freezes or can't find a signal. If epilepsy or any other condition makes you sensitive to flashing lights, you can turn the LEDs off.

How do I turn off the LED lights?

Find the Heart Rate setting on your tracker and turn it off to stop the blinking lights. You must change the setting to Auto or On to resume heart rate tracking.

Why don't I always see my heart rate?

Occasionally your tracker may have difficulty getting a strong signal. If you don't see your heart rate on your tracker, first make sure you are wearing it correctly. Experiment with placing the tracker higher on your wrist; because blood flow in your arm increases the farther up you go, moving the tracker up a couple inches can be helpful. Also, make sure you're not wearing your tracker too tightly; a tight band restricts blood flow, potentially affecting the heart rate signal.

After a short wait, you should see your correct heart rate again. If this reading persists, try changing your Heart Rate setting from "Auto," which means the heart rate tracker is usually active when you're moving, to "On," which means the heart rate tracker is always active.

Changing the Heart Rate setting to "On" does increase battery usage, so you'll probably want to change it back to "Auto" later when the signal is strong once again. If you're still unable to get a heart rate signal, please contact Customer Support.

Why does my dashboard show a different heart rate measurement than my tracker?

When hovering over the heart rate graph on your dashboard, the heart rate measurement shown is a five-minute average. For a minute-by-minute display for a particular workout, click that workout on your dashboard's Recent Exercise tile.
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Last updated: April 27, 2017
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