We answer how it works, how accurate it is and what’s coming soon
Over time, the Apple Watch has grown into quite the everyday smartwatch. But while it does an ample job of handling your notifications and providing third-party apps, its real chops lie within activity tracking.
Through Apple’s Activity app, you’re able to get a look into the basics, such as burned calories, active minutes and how many hours you moved within a day, while Workout handles more detailed sports tracking. And it’s here where the smarts of the Apple Watch’s heart rate monitor are most prevalent.
But how does it all work, what data is presented and just how accurate is the tracking? Well, read on for all the answers.
How the Apple Watch heart rate monitor works
Almost every smartwatch harbouring a heart rate monitor makes use of the same technology, and the Apple Watch is no different.
Photoplethysmography, as its known, essentially works on this premise: blood is red because it reflects red light and absorbs green light. Therefore, by using green LEDs and pairing them with photodiodes, a device is able to detect the amount of blood flowing through the wrist. When your heart beats, this flow, and by proxy the green light being absorbed, is greater. Between beats, meanwhile, it’s less. In order to attain the most accurate BPM data, these LEDs flash hundreds of times per second.
This technology is also used during the Watch’s Breathe app, which focuses the user on relaxing, as well as, new through watchOS 4, provide insight into the walking average BPM and heart rate variability.
However, it’s not just bouts of exercise in which the heart rate monitor is in action. It can also utilise infrared light to measure your heart rate in the background and give you a heads-up if your heart is spiking to dangerous levels.
Apple Watch heart rate monitor: The data and the apps
We’ve talked about how the Apple Watch collects heart rate data, but what data does it actually present?
Well, on the wrist itself, you’re given your real-time heart rate during exercise and can view your average heart rate for the entire workout once you’ve finished.
If you’re simply at your desk and want to see how your heart is getting on, simply head to the Watch’s Heart Rate app, which also provides insight into your resting, walking, workout, and recovery rates throughout the day. You can even shoot straight to the app from your watch face by adding a complication, like we have below. Not sure how to do that? Head to our Apple Watch complications guide.
You also have the option to receive notifications from the app when the Apple Watch detects your heart rate rising above, for example, 120 beats per minute while you appear to be inactive. The easiest way to enable and adjust this is by heading to the Watch app on your iPhone, scrolling down to Heart Rate in the My Watch section and tinker with the settings which suit your ticker.
On the iPhone, meanwhile, you’re able to view all your workouts, which should then open up into a more detailed graph showing how your heart rate fluctuated throughout the activity, and also how your heart recovered in the three minutes following the end of your exercise.
And while these are all useful ways to provide you with a more detailed look at your heart rate, the downfall here is that there’s no real interpretation of that data. While you have an indication of when your heart rate was high and when, there’s no breakdown of how much time you spent in each heart rate zone or any VO2 Max data.
However, more dedicated third-party apps are aiming to fill this gap. Both Cardiagram and HeartWatch will give you a live look at heart rate zones, while also providing a more detailed insight into your heart rate history.
The third-party action isn’t limited to heart health, either. Fitness platforms that support heart rate tracking, such as Strava, are also able to tap into the tech in order to interpret your data more fully – perfect for those who don’t want to use Apple’s proprietary tracking apps.
This is all fed back to Apple Health, too, where you can edit just which peripheral devices and apps can track your heart and feed into the overall picture. This is ideal for helping you see a weekly, monthly or even a yearly picture of the data you’ve collected, something which isn’t available on board the Apple Watch itself.
Apple Watch heart rate monitor: Let’s talk about accuracy
It all sounds good in practice, but it’s all down to whether this can truly deliver an accurate monitoring experience from the wrist.
And for the most part, the Apple Watch does this as well as any wrist wearable on the market. After all, while the same technology is being used to gather the data, it’s how this is then interpreted, which leads to accuracy or inaccuracy.
Through our testing of the Watch against a chest strap over the last few years, we’ve found it to be one of the more consistent performers. However, that doesn’t mean it’s free from the same limitations as the rest of smartwatches and fitness trackers using optical sensor tech. That is, when drifting quickly between low and high beats per minute during HIIT, it can often struggle to keep track in time.
In our experience, such as the example below, we tend to see average heart reading slightly higher than the number give by chest straps, but this is nothing too drastic if you’re just looking to keep a basic tab on your beats.
(Apple Watch Series 3 – left – compared to the Polar H10 chest strap – middle and right)
It’s also worth pointing out that, in order to receive the most accurate results, you need to ensure that the fit on your wrist is right. That means you can’t have it too tight, or too loose. Your skin needs to be in contact with the sensors at all times, but with room left for your skin to breathe.
Apple Watch heart rate monitoring: What’s coming next?
Apple has pivoted itself towards health and fitness recently, announcing its atrial fibrillation study and offering more wellness features, such as heart rate notifications, through the Watch.
But the big step here is upgrading the current photoplethysmography method of monitoring to the ECG, medical grade tech — the same currently found in chest straps. And according to reports, it’s a development that could show its face through the Apple Watch Series 4, if the Cupertino company can receive the required FDA clearance.
While ECG monitoring is considered more accurate than current wrist-based methods — good news for exercisers — it’s also more effective at spotting heart abnormalities, potentially notifying users of problems before they become more severe.
If this is indeed something Apple provides sooner rather than later, expect the data available to users to take a big leap forward. And for those of you who can’t wait for the ECG tech to hit the wrist, startup AlivCor has already developed a strap solution, the Kardia Band, which is able to give users the readings.