​Optical HR accuracy: The experts speak

We ask the experts what they think of optical heart rate technology
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A couple of weeks ago I wrote a piece born of frustration with the current crop of optical heart rate sensors. After we reviewed the Garmin Vivosmart HR, Forerunner 235 and Polar A360, it wasn't a surprise that they weren't as accurate as chest straps – but I felt brands weren't being upfront about the shortcomings of sensors.

Read the original: We need more honesty in heart rate tech

Once the article was published, a host of companies got in touch wanting to add their two cents to the issue. And I was interested to find out from the experts whether wrist monitors could ever be accurate, whether the data from them is really junk, and if people are being misled?

I caught up with three industry experts, including the inventor of the optical heart rate sensor, to get their takes on the matter.

Dave Wright - MyZONE

CEO and creator

​Optical HR accuracy: The experts speak

"The whole optical blood flow thing is great if all you're doing is walking or running. And if that's all you do, they're not too bad.

"But when you start building a live display into ecosystems and you're guiding your training by it, that's when you can't afford to have any delay. Consumer demand for credible data is so high now, they don't expect anything less.

Essential reading: Fitbit Blaze review

"That's the thing with a lot of these optical blood flow wearables. If you're just walking and running then they have good algorithms to get rid of light and movement artefacts, but if the intensity is a lot higher, above 160 beats, then the blood passing is so fast that when you add movement as well, it becomes really difficult to get the right reading.

"It's physiology not technology. It's a matter of the unpredictability of the blood through the wrist in an area you can't control. Ear tech is going to beat the wrist because it suffers less physiological interference.

"Anything more than a one or two second delay isn't acceptable. The reason being that HIIT sessions are about pushing people to the limit. If you're doing 10-20 second intervals and there's a delay of 10 seconds, it's beyond unacceptable.

"Not naming names, but one company have been desperate for us to use their device. I used it for a standard workout, doing burpees and it was taking 1 min and 25 seconds before it caught up with MyZONE. I deemed the data irrelevant.

"Where Fitbit have got into a little bit of trouble is because they're saying they're not a medical device and they say that it's not capable of doing high intensity activity, but the advertising shows exactly the activities that they know aren't accurate."

Chris Eschbach – Valencell

Director of exercise science & clinical trials

​Optical HR accuracy: The experts speak

"It's in our interest to do detailed validation and testing of all optical heart rate devices on the market. Accuracy is heavily dependent on where the sensors are located and what the person is doing. The wrist has less tissue, more bones, more tendons and if there's not great blood flow then accuracy goes down.

"We took two chest straps (chest straps are awesome for accuracy because they use electrical signals but we put electro gel on the back for good conduction) and we put the chest straps on a group of 20 people. They performed a test on our treadmill with a mix of walking, running, walking, standing and running at a higher speed for dynamically changing heart rate and step rates.

"When we analysed the chest strap data we're getting about 91% of all the data within +/- 5 BPM of each other. Now if we move to earbuds and arm bands they're nearly there too, around 91% accurate compared to a chest strap between +/- 5 beats. Our wrist tech was around 85% within that +/- 5 beat range when running.

"When you go to other activities, it's a whole different ball game. During cross fit or weight lifting, the head is a great location, good blood flow, stable and a good fit, as is the upper arm. The wrist can completely crap out. If you're doing pull-ups or arm curls, they may not be measuring at all.

"We're getting better. It will be equally as good as the chest strap in certain situations, but there will be weaknesses it has and others don't.

"When you're measuring heart rate I want to be within that five beat window to be really meaningful. If we're using heart rate to measure intensity levels or an input for calorie expenditure, or how much training has affected you, you're either measuring it accurately (within +/- 5 beats) or you're not. If it's not, then let the user know the data is worthless. And that's not the case right now. No-one is telling users if the data is horrible, and they should."

Liz Dickinson – Mio Global

Mio CEO and inventor of optical heart rate tech

​Optical HR accuracy: The experts speak

"For us the most important thing was getting rid of the chest strap. Over time optical will become good enough if not perfect. It's not quite there yet, but it's a lot better than when I invented it a few years ago when it couldn't even do continuous sensing.

"Its usefulness right now depends on what you want to use data for. I would say that optical is useful for running and cycling and some are useful for daily life – but nothing out there today is at the level of the chest strap. That's the fact, but I don't think anyone is saying that's not the case. What we're saying is that if you don't want to wear a chest strap then there is an alternative.

"The more athletic you are the more likely you are to wear a chest strap. What we're trying to do is to democratise access to HR training and the only way to do that is to get rid of the chest strap. We want people to have a great experience when they're working out and we believe heart rate is the most important thing for people to understand in health and fitness.

"In terms of honesty, I haven't reviewed marketing literature of other brands to say whether they're misleading people or not. But you have to be careful. The tech works differently on different people, because body fat or blood diffusion isn't the same as other people."

Wareable verdict

So what have we learned from talking to the experts of heart rate tech? Well firstly, if you're serious about your sport and data today, then steer clear of the wrist monitor. It's a great way for entry level runners and fitness fans to take control of their plans, but for those using the data to train, it's not up to task.

And while runners may one day be able to use optical tech for training sessions, when lag times and algorithms improve, for gym bunnies and HIIT fans it looks unlikely that the wrist will ever be a serious option.

But there does seem to be a light at the end of the tunnel. Our experts agreed that the ear is going to become a key place for future sensors, and it's a place we're already comfortable with placing tech. Hearables here we come.

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James Stables


James is the co-founder of Wareable, and he has been a technology journalist for 15 years.

He started his career at Future Publishing, James became the features editor of T3 Magazine and T3.com and was a regular contributor to TechRadar – before leaving Future Publishing to found Wareable in 2014.

James has been at the helm of Wareable since 2014 and has become one of the leading experts in wearable technologies globally. He has reviewed, tested, and covered pretty much every wearable on the market, and is passionate about the evolving industry, and wearables helping people achieve healthier and happier lives.

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