Heart rate monitoring is now a big part of the wearable agenda. Whether it's packed inside a Fitbit fitness tracker, a piece of smart clothing or a fitness-focused sports watch. It's there, ready to serve up that extra layer of biometric data.
But while tapping into the heart is now more widespread than it has ever been, accuracy is still a problem, specifically from optical or light-based heart rate sensors built into wrist-worn devices. The pool of wearables we'd comfortably recommend to do a good job remains very small.
While there's a trend to move sensors to other locations on the body, many companies still persist with positioning them where they are simply not good enough to deliver reliable data.
Valencell, a company that develops biometrics sensor systems for wearables including ones made by Samsung, Jabra, Bose and Suunto accepts that even its own best technology struggles to deliver great accuracy from that part of the body for users who rely on that heart rate data to be on the money, all of the time.
The problem with HR from the wrist
"The wrist is about the worst place on the body to get an accurate measurement," said Dr. Steven LeBoeuf, Valencell's president. "If you have a single strap device and you can get someone to wear it with the right tightness, then you can get good readings. The problem is, if the person is typing on a keyboard or doing a gym activity where they are moving their wrist then you're going to get completely erroneous readings."
Fit is not the only issue here that can impact on measurements. Skin tone and tattoos have also been known to compromise readings. LeBoeuf recognises another problem impacting on measuring heart rate from the wrist. "Even with our best technology, the heavier device, the more likely you are going to see failure," he said. "A thick heavy wristwatch like the Suunto Spartan Sport Wrist HR made it really hard for us to get accurate heart rate in that device just because of how it heavy is."
The wrist is about the worst place on the body to get an accurate measurement
Valencell carries out all of its own thorough testing in its labs and tells us it likes to be part of the development process with hardware partners as early as possible. That doesn't however always stop from devices getting out that are not fit to do the job, which has proved frustrating for LeBoeuf and his team.
"When we evaluate heart rate monitors. I can't tell you the amount of times where we've helped a partner build these modules. They perform a test and they say great, we're done and we say no, you're not done," he said. "You need to try this out on multiple people.
There was a report out on Fitbit accuracy recently where readings were off by 30 bpm. Some time for other people the device will be spot on. Don't just put a sensor in and get a good a reading on a day and think you're done. It's frustrating when someone tests an inferior product and think it's fine. It's frustrating when people take our sensors and get great results but we know they haven't implemented it well because they have only tested once on one or two people."
From the ears and the head
While Valencell is critical of the wrist, it's more upbeat about other areas of the body that it believes can do its technology justice. Those areas are the ears and the forehead. We've already seen the likes of Jabra, Bragi, Bose and Under Armour explore the ears as a place to take those readings with varying results. That's because you need to make sure you get the right fitting earbud. When you do, LeBoeuf believes that makes readings "bulletproof" no matter how aggressive or vigorous your workout is.
Currently, only the Moov with its HR Sweat headband and its yet to be released HR Swim swimming cap has taken advantage of the approach to take readings from the head. So why are these options actually better than the wrist? "The forehead and the ear is really good for profusion," he explained. That's the delivery of blood to a capillary bed in a tissue in case you were wondering. "The wrist is really poor for that," he said. "If you have a scratch on your wrist for example, it might just clear up right away or leave a small red mark. But if that happened in the ear, you feel like you are going to bleed to death and that's because of all the profusion in that area.
One of the of good things that we like about the ear is that it's one of those areas where you can get assessments of blood pressure and other biometrics that you simply can't get on the wrist because the pressure wave is so diminished by the time it gets to the outer skin of the wrist."
Hardcore v lifestyle HR metrics
While heart rate has largely been associated with fitness, things are changing quickly as more wearables explore the idea of monitoring our mind as well as our bodies. Garmin's new Vivosmart 3 uses HR variability data to provide stress scores while Fitbit also taps into this for its mindfulness features. What we are now seeing is not just a demand for heart rate data, but the ability to produce metrics that cater for different kinds of people and needs.
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Valencell sees this as a break down of 'exercise' and 'lifestyle' use cases for the biometric data. Whether you want a hardcore metric like VO2 Max or HRV, it really does matter what part of the body you get that information from.
"If you want to know somebody is at risk of a cardiac event for instance, you want to measure more accurately frequently," LeBoeuf said. "If you've played around with some of the popular wristband devices out there and you start typing it starts picking up your typing rate not your heart rate. That's a big weakness. A lot of people want to measure health issues, but what if you are sitting at your computer all day? You can't measure them properly. It's a big issue.
"It's really difficult to deliver heart rate variability from the wrist when you have so much movement of the wrist. Our technology works best when people are not moving. We are developing some technology that we are launching later this year that takes care of the wrist situation for this lifestyle motion issue. The ear is much more straightforward. If you have an earpiece on, we can monitor that HRV data that can be used for stress analysis, arrhythmia detection and much more."
The key to improving wrist HR
Don't write off optical heart rate monitoring from the wrist all together. While it might not be the best fit for VO2 Max or HRV right now, it can still have its benefits for other heart rate metrics as LeBoeuf explained.
"There are other things that don't require as much accuracy," he said. "Like if you can accurately measure someone's average heart rate during the day. Take the Mio guys for example, they talk about PAI analysis used in its app and Mio Slice wearable that's based on the long-term HUNT health study. You can follow those these things that don't require the high precision you need for VO2 Max. It still requires you to have an accurate heart rate monitor, but it doesn't need to be as precise."
The company is already working on ways to improve that accuracy but believes it could be some time before we see it inside wearables we can actually get our hands on. That's based on the amount of time it took to get its existing technology to market but there are reasons to be positive that things are going to get better.
"As far as making the wrist bulletproof for heart rate, is it possible? Yes. We have something where we can control the pressure in the heart rate monitor device," LeBoeuf said. "Another way to do it is through sophisticated signal extracting technology."
One way to improve accuracy from the wrist is to make something that's extremely lightweight. "One of the things we are seeing with people working with our technology, is to make these very thin and very light bands that are literally biometric signal collectors," he said.
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"They might just wear this with a smartwatch. I do expect you'll see in 2018, companies start to market almost like a Livestrong band, because it is lightweight and has less complications. I call it an idiot band, it's not really smart, it's just collecting the data and sending it to a device to do all the data crunching and you won't have to think about charging it."
Valencell is beginning to see more medical companies reach out to use its tech as well for cardiac monitoring and respiratory monitoring in various different forms from wrist devices to patches. While new metrics hit the scene, the company believes heart rate will remain a staple feature for wearables and will become more accurate and versatile while using assessment tools to provide the kind of meaningful data that will be even more valuable and insightful.