Heart rate FAQs

HOW DOES MY CHARGE HR OR SURGE TRACK 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.

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WHAT ARE HEART RATE ZONES?

Heart rate zones can help you optimize your workout by targeting different training intensities. Your zones are calculated based on a percentage of your estimated maximum heart rate. Fitbit calculates your max 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 heart icon on your tracker tells you your zone at a glance. 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 heart rate zone. Log into your dashboard and click the gear icon in the upper right. Choose Settings > Personal Info. There you can choose between the default three zones or enter your own 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.

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. Your tracker estimates your resting heart rate by measuring your heart rate while you’re asleep and while you’re awake but still during the day. Therefore, for best accuracy, wear your tracker to sleep. Note that your minimum heart rate during sleep is typically lower than your resting heart rate.

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. Do not be concerned if occasionally during intense exercise your heart rate goes above your Fitbit-calculated max heart rate.

WHAT IMPACTS THE ACCURACY OF MY HEART RATE READING?

As shown in the Surge illustration below, for all-day wear when you are not exercising, your tracker should usually rest a finger’s width below your wrist bone and lay flat (as you would usually wear a watch). Do not wear your tracker with the display on the inside of your wrist.
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As with all heart-rate monitoring technology, whether a chest strap or a wrist-based sensor, accuracy is affected by personal physiology, location of wear, and type of movement. In other words, not every person will get a perfectly accurate reading with every type of exercise. For best 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 spinning 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.

HOW DO I CHANGE THE HEART RATE SETTING ON MY TRACKER?

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

The default setting of Auto is appropriate for most people; the heart rate monitor 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 monitored even though you are wearing your tracker, you can choose On. If you aren’t interested in heart rate monitoring or want to maximize battery life, you can choose Off.

WHAT IS PUREPULSE?

Our PurePulse heart rate monitoring 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.

HOW ACCURATE IS PUREPULSE COMPARED TO THE COMPETITION?

We have performed multiple internal studies to rigorously test the accuracy of PurePulse against heart rate chest straps, and we see only a small percentage difference across a variety of workouts. Unlike chest straps, PurePulse is designed for all day wear and tracking, giving you a more complete picture of your health and fitness. By comparison, chest straps are only designed to be worn for a short duration, during exercise. They tend to be uncomfortable and can stop working if the skin is not kept damp during wear.

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?

The LED lights are safe for skin and are on the visible spectrum, similar to the lights in your home or office. Allergy to visible light is extremely rare. Additionally, the LED lights used are very low power so they will not burn the skin and are programmed to shut down if your device freezes or does not see the right signal.

CAN I TURN OFF THE LED LIGHTS?

To help maximize your tracker’s battery life, you can turn off the blinking LED lights. To do so, access Settings through your fitbit.com dashboard or a Fitbit app, and turn Heart Rate Tracking or Backlight to off. This will turn off heart rate detection and measurement, and needs to be set to On or Auto in order for the function to work.

WHY DON’T I 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 and you have a Surge, try changing your Heart Rate Tracking setting from “Auto,” which means the heart rate monitor is usually active when you’re moving, to “On,” which means the heart rate monitor is always active.

Changing the Heart Rate Tracking 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.

CAN I SEE LIVE HEART RATE DATA ON MY MOBILE DEVICE?

You can see live heart rate data if you use the Fitbit app for iOS or the Fitbit app for Android with your Surge or Charge HR. For Windows phones, we currently only support live heart rate data for Surge.

If you’re using the iOS or Windows Phone app, make sure Bluetooth and All Day Sync are turned on. To manage the All Day Sync function, open the Fitbit app and select your tracker, then tap All Day Sync to turn it on or off.

If you’re using the Android app, you’ll only see heart rate data if you have notifications enabled. To set up notifications see How do call notifications work on my Force, Charge, or Charge HR? or How do I receive call notifications and text messages on my Surge?

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