With the introduction of its first true smartwatch last year, Fitbit's range of trackers have grown into a well rounded crop. And while every one of its wearables is able to track the basics, some offer tech that goes much further than tracking your steps.
Thanks to the in-built heart rate monitor found in the Fitbit Charge 2, Fitbit Alta HR, Fitbit Blaze and Fitbit Ionic, you're able to gauge not only your heartbeat activity during workouts, but also tap into wellness features and some of the best sleep tracking in the business.
Read this: Which Fitbit tracker should you buy?
Below we'll break down how it all works, how you can customise it to suit your activity and how to ensure the most accurate results. Any questions? Let us know in the comments section below.
How Fitbit heart rate monitoring works
Similar to how we covered the tech for the Apple Watch heart rate monitor, let's give a quick breakdown to how pretty much all wrist-based heart rate monitoring works.
Photoplethysmography essentially works upon one simple premise: blood is red because it reflects red light and absorbs green light. So by using green LEDs and pairing them with photodiodes, Fitbit uses its own in-house PurePulse technology to detect the amount of blood flowing through the wrist.
Read this: Heart rate tracking from around the body
When your heart beats, this flow, and as a result, the green light being absorbed, is greater. These lights are then flashed hundreds of times per second in order to gain the most accurate BPM (beats per minute) data.
Naturally, while every company dabbling with this optical sensor technology is working from the same blueprint, how each company's algorithms interpret the data affects how accurate the readings are.
How to view your heart rate on a Fitbit
Below we'll get into the intricacies of the heart rate monitor, but it's worth pointing out how you can actually view your heart rate data, too.
Depending on the device itself, you should be able to see your current BPM on the home screen or by swiping. For detailed info from your exercise or on resting heart rate, you'll need to head to the Fitbit app's dashboard and tap through to the Heart Rate section and select the day you want to view. The same also applies to the Fitbit web app.
Resting heart rate while you sleep
It's not all about your heart rate when you're exercising, remember. Fitbit's trackers are also able to keep track of your resting heart rate — a metric which refers to the heart rate measurement when you're awake, calm and have not recently exerted yourself.
In order to estimate this, Fitbit interprets data taken from when you're awake and when you're asleep, meaning that those who take their device off before bed won't receive the most accurate results.
Typically, your resting heart rate is higher than your heart rate while you're asleep, so don't start panicking if you notice that the figure is higher than the lowest number you see in your graphs.
VO2 Max for serious fitness data
While VO2 Max - the metric which essentially calculates the maximum amount of oxygen that an individual can utilise during intense exercise - has made its way onto a large number of sports watches and even hearables, Fitbit has a different name for it - Cardio Fitness Score.
To access your score, simply head to the heart rate section of the Fitbit app and swipe the graph across. The higher your score, the better your fitness, and Fitbit will help determine where you sit on the scale by looking at your age, gender and resting heart rate. For more on understand the metric, read our VO2 Max guide.
Fitbit heart rate zones
Heart rate zones are essentially groupings, which allow you to adjust the intensity of your training based upon how long you spend in certain stages.
Through your Fitbit, you'll be assigned your maximum heart rate, which is configured by the usual method — 220 BPM minus your age — and from there your heart rate zones are also established.
At the top is what Fitbit labels as your Peak Zone, which means your heart rate is above 85% of its maximum. Next below is your Cardio Zone, which covers the ground betwee 70% and 84%, before scaling down to the the Fat Burn Zone when your heart is pumping at between 50% and 69% of its maximum. Anything below 50% of your maximum heart rate is considered Out Of Zone.
Essential reading: How to train with heart rate zones
If you're looking to train in one particular zone, Fitbit tries to simplify this by mixing up its heart rate icon for each zone. The Peak Zone will have the heart icon resting above two dashes, the Cardio Zone will have the heart in between two dashes and the Fat Burn Zone will have the heart below two dashes. When you're Out Of Zone, only an outline of the heart icon will show.
How to customise Fitbit heart rate zones
It's all well and good knowing about your heart rate zones, but it's also nice to have a bit of control over them. And there's two ways to customise things.
If you're working from the Fitbit app, head to Account from the app dashboard and scroll down to Heart Rate Zones in settings. From there, you're able to add a custom zone and also adjust your max heart rate.
To change the same things from the Fitbit web app, head to the dashboard, select your gear and head to settings and personal information.
Using heart rate tracking to keep calm
Heart rate variability, which is calculated by looking at the time in between heartbeats, is another measurement used by Fitbit to keep a track on your heart. However, since this is focused on tracking fluctuations, things like a user's age, body position, the time of day and health status can all affect readings.
Debuted through the Charge 2 and also available on the Ionic and Blaze, Fitbit's Relax app measures the beat-to-beat changes in order to recommend a personalised breathing pattern during each guided breathing session.
However, these are more of a real-time way to get you to focus on relaxing, as opposed to something you view in the companion app and keep a track of in the long term. You're able to choose a session lasting either two or five minutes, and all you need to do is follow the circle on the screen for inhaling/exhaling. Sparkles will show after around 20 seconds if you're aligned to the device.
You can read more in our heart rate variability guide.
Working out that calorie burn
Firstly, your Fitbit device will take into account your basal metabolic rate (BMR), which is the calories that burn by maintaining necessary body functions like breathing, heartbeat, and brain activity.
This BMR accounts for around half of your daily calories, with this estimated from the gender, age, weight and height you enter when setting up your device. And with the tracker resetting the stats at midnight, this is why you'll notice calories already burned when you wake up - your still burning as you sleep. Naturally, Fitbit will also be adding on the calories you burn through activity.
If you're looking for more on this, we've gone into detail about how calorie burn estimates actually work.
Fitbit heart rate data by device
Naturally, with Fitbit's heart rate tech involved in both fully fledged smartwatch and fitness trackers with smaller screens, what you see depends on which device you have on your wrist.
The devices which actually offer heart rate monitoring are the Fitbit Ionic, Fitbit Blaze, Fitbit Charge 2, Fitbit Alta HR and the now-discontinued Fitbit Surge. And while the PurePulse tech is consistent throughout, meaning the results should be the same no matter which tracker you wear, things are displayed slightly differently.
This is primarily in relation to heart rate zones. Above we noted how this is displayed through a heart and dash icon, but some will feature a dot instead of a dash. Meanwhile, the Fitbit Ionic's heart rate icon may sometimes be greyed out if the device is searching for a stronger reading.
How to get accurate Fitbit heart rate data
Like with any optical heart rate solution, Fitbit's PurePulse technology is solid but not without its issues. Fluctuating between high heart rate and low heart rate during interval training can often prove to be problematic for the heart rate monitor to keep up with, though, as we say, Fitbit's trackers aren't alone in this problem.
If you sense your Fitbit device isn't quite tracking your heart rate correctly in normal , there are a couple of things to keep in mind. When you're not exercising, wear your device a finger's width below your wrist bone. And when you are exercising, consider wearing the device slightly higher on your wrist for more accurate readings, since some exercises will cause your wrist to move frequently.
Naturally, as with any wrist-based monitor, you'll also need to make sure the back of the watch is touching the skin at all times, while also ensuring it isn't strapped too tightly onto your wrist.