Tech Trends: The End of Chest-Worn Heart Rate Sensors?

The optical sensor sits on the back of the watch, such as on this Mio Alpha 2.

The open secret about traditional heart-rate sensors is that no one really wants to wear them. Don’t get me wrong, these sensors provide helpful training information, but the awkward and constrictive nature of the chest strap can be a dealbreaker. For many runners, heart rate data is not worth the hassle.

Until recently, those looking for a more comfortable way to measure and record that data were out of luck. Optical heart rate sensors built into wrist-worn devices provide a new alternative. This technology is an important component of some current generation fitness trackers, smart watches and GPS running watches. Some notable devices include: Apple Watch, Fitbit Surge & Charge HR and Garmin Forerunner 225. This shift to optical sensors is not a small development, but one that could signal the beginning of the end for chest straps.

How does it work?

An optical heart rate sensor determines heart rate through a process known as photoplethysmography. The sensor consists of LEDs and an electro-optical cell. The LEDs shine light into the skin, enabling the electro-optical cell to detect the pulsing volume of blood flow. Since blood absorbs light, fluctuations in light level are correlated to heart rate. A traditional sensor measures heart rate differently with two areas that determine heart rate by measuring the bio-electric impulse that occurs when your heart beats. The number of impulses the sensor counts corresponds to the same number of heartbeats over the same amount of time.

How does it help training?

If a chest strap was a dealbreaker, a wrist-worn device with an optical sensor gives runners the opportunity to collect and analyze data they had previously been missing. Heart-rate information is another useful metric to aid training and recovery. While one should never be a slave to the numbers or a device, monitoring heart rate in addition to listening to body signals can provide valuable feedback. With this data, heart rate zones can be determined to optimize intensity levels for workout sessions and to help athletes maximize recovery by controlling their effort on recovery runs.

Comfort, but at what cost?

Along with a more comfortable fit and the ability to collect more data, there are a couple of other advantages to owning a device with an optical sensor. It’s nice to no longer need to wash a dirty and sweaty chest strap. Since devices with optical sensors are rechargeable, there is no need to purchase and replace batteries as required with traditional sensors.

While these are distinct advantages over traditional heart rate sensors, optical sensors are a new technology. Like any new technology, there tend to be growing pains and trade-offs. Currently, the quality and accuracy of the data varies quite a bit between device types and sensor manufacturers. Most fitness trackers with optical sensors do a good job with measuring resting heart rates but may lag or lose accuracy at high heart rates. Sensors also can have difficulty determining heart rate for people with darker skin tones. While devices with optical sensors provide similar data as traditional heart rate sensors, the lack of chest strap will cost you. The new Garmin FR 225 with optical sensor costs $300, while the Garmin FR 220 (which does lack a couple of the 225’s fitness tracking features) and traditional heart rate sensor sells for $250.

While not perfect (and more expensive), optical sensors make heart rate data more accessible to people who refuse to wear a chest strap. Along with the additional data, the comfort and convenience of these new devices could make traditional heart rate sensors a thing of the past.

RELATED: Running’s Wearable Tech Boom

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About The Author:

Jim McDannald is a surgically trained podiatrist who writes health/fitness technology product guides for TheWirecutter.com and coaches distance runners at McGill University. 

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