Heart Rate Monitors: Optical vs. Chest-Based. Which is better?

Nowadays it seems that almost everybody is wearing an activity tracker or smart watch on their wrist. The majority of wrist based activity trackers will give you information about your step count, your sleep quality and your heart rate. Is an optical sensor accurate? How does it know your heart rate? Is the data that you see on your watch correct? What device is best for me? We answer your questions.
Apple Watch heart rate guide: How to use all of Apple's HR features
What is an optical heart rate monitor?

Optical heart rate monitors are found on the underside of most smart watches and activity trackers. They usually appear as a set of small bulbs and sensors which shine a strong green light periodically. The information they detect is shown and stored on the watch.

How does an optical heart rate monitor work?

When your watch is on your wrist, the light shines through your skin in to your blood vessels. Your blood vessels expand and contract at the same rate as your heart beats as blood is pushed through them. The amount of light that bounces back and hits the sensors beside the bulb changes as the blood fills and leaves the vessels. The sensors measures how often the amount of light bouncing back changes, and converts this to beats per minute.

The process is called photoplethysmography (PPM) and has been used in the medical profession for long time as a non invasive, cheap way to measure somebody’s current heart rate.

What is a chest based heart rate monitor?

A chest based heart rate monitor is usually an elastic strap with a small detachable device that has the ability to detect electrical signals.

How does a chest based heart rate monitor work?

Each time your heart beats, an electrical signal stimulates the muscle in the wall of your heart. This electrical stimulation makes the walls contract, which forces blood out of the heart. That starts the blood’s journey around your body.

Support: Using a Garmin Heart Rate Monitor - YouTube

Your skin always has moisture on its surface, even when you are not sweating. Water is a great conductor of electricity. When you put a chest based heart rate monitor on your skin, it traps some moisture between the heart rate monitor and your skin.

The chest based heart rate monitor has electrical impulse detectors on the underside of the device. It simply counts how many electrical impulses are detected in the moisture, and usually stores the data for you to view on your phone.

This is the same technology used by fancy, expensive machines in health care, such as ECG machines.

Which one is more accurate?

It might be fair to say that, given optimal conditions, both forms of monitoring heart rate are equally effective.

However, we here at RunWay Running unanimously agree that, for exercise, chest based heart rate monitors are much more accurate. There are a number of reasons for this.

Firstly, as you exercise, you sweat. When moisture builds up between the heart rate monitor’s detector and the skin, the ability to detect electrical impulses increases. So, for less demanding sports where one does not sweat so much, this might not be a factor. For running, it definitely is.

Secondly, as you exercise, your wrist based activity tracker will inevitably move around on your wrist. It is recommended that, for optimal heart rate tracking results, you place your activity tracker about 2 finger widths above your wrist bone. This is because there are fewer blood vessels close to the skin around your wrist bone. We here at RunWay Running have found that if you tie your activity tracker tighter to avoid movement, you can actually cut the blood supply of the blood vessels closer to the skin, which is both uncomfortable and leads to inaccuracies.

Finally, chest based heart rate monitors are able to detect actual heart beats. Wrist based optical heart rate monitors rely on the detection of blood vessels that increase and decrease in volume at your wrist. This can lead to the detection of false data, especially if your heart rate is increasing and decreasing often during a workout, such as what happens during a hill session or any HIIT style workout.

What does RunWay Running recommend?
Budget option: Polar H9
£52/€58/$63

If you are on a tight budget, but you know that you can get a new personal best over 5km if you just get in tune with your heart rate stats, a chest based heart rate monitor like this Polar H9 is a really great option. The battery life is phenomenal as it relies on old school, shop-bought batteries. You’ll get about a year of use out of one battery if you train for an hour every day. If you want to upgrade your set up in the future, the Polar H9 is compatible with a range of fitness tracking products using bluetooth and ANT+ technologies.

Splashing Cash: Garmin HRM Run
£80/€90/$100

The Garmin HRM Run is more than a heart rate monitor. With inbuilt cadence detection, stride length detection and a whole host of other great features, this chest strap is a great running device.

Triathlon Choice: Garmin HRM Tri
£99/€110/$120

The Garmin HRM Tri is all that the HRM Run is, and more. It has the capability to measure all the same data as the HRM Run but can also detect your heart rate underwater. Its neat enough to go under your tri-suit too without bulging, which gives it a thumbs up from the RunWay Running crew!

Garmin Bundle: The Forerunner 735XT + HRM Run
£350/€390/$425 £210/€235/$256!

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