How Accurate Is the Heart Rate Monitor on a GPS Watch?

A heart rate monitor is a small device that continuously shows how much your heart beats throughout the day. This metric is called your heart rate, and it’s a significant physical metric when talking about exercise or serious sports as it determines how hard your body is working.

If you’re a runner, having a heart rate monitor gives you lots of benefits. It can tell you which parts of your running session your body works the hardest, as well as how long it works hard. You can also use your heart rate to determine how fit you are by comparing your results with your resting heart rate and previous results.

There are two kinds of heart rate monitors that runners and other athletes typically use: chest straps and wrist-based–the kind that you see on a GPS watch. Chest strap monitors have already been tried and tested throughout time, but some still question the efficacy of the more modern wrist-based monitor.

Don’t worry, that’s what we’re here for. This article will answer the question and settle the debate once and for all.

Wrist-Based Heart Rate Monitor

Prior to the invention of wrist-based monitors, heart rate monitors used to be strapped to the chest in order to work. This makes sense since the chest is the closest place to the heart. While it may be inconvenient, there’s no doubt as to its effectiveness.

However, as time went on, technology also improved. One extremely helpful innovation is the wrist-based heart rate monitor. Previously, they were nothing more than a glorified bracelet that could measure your heart rate, albeit not with the same precision as chest monitors.

Now, wrist-based heart monitors are packaged inside watches. They track your heart rate through a technology called photoplethysmography (PPG), which uses light to calculate the way your blood changes volume as your heart pumps, effectively and accurately counting each time your heart makes a beat.

And that’s not all. Performance watches and smartwatches with heart rate tracking also usually have more features useful for all runners and athletes.

For example, smartwatches such as various Fitbit watches measure heart rate zones, as well. This feature analyzes how much effort you’re putting in to maintain your ideal exercise heart rate and will even actively motivate you to push yourself even further.

How Accurate Are Heart Rate Monitors on GPS Watches?

That said, are heart rate monitors on GPS as accurate as chest monitors?

Older wrist-based monitors were known to suffer from inaccurate numbers. This isn’t too surprising, due to the novelty of the technology.

However, multiple scientific studies have reported that wrist-based heart rate sensors that use optical technology exhibit acceptable levels of accuracy.

For example, one study done by Xie et al. (2018) recruited 44 test subjects and made them simultaneously wear six devices to measure different kinds of activities throughout the day.

The result revealed that the wearable devices displayed a rather high accuracy of heart rate measurements. The same goes for other metrics such as steps, distance, and sleep metrics, proving that technology has certainly progressed a lot over time.

Another more recent study done by Chow and Yang (2020) gathered 40 young and older adults and asked them to undertake a series of activities while wearing two brands of wrist-based sensors: Garmin Vivosmart HR+ and Xiaomi Mi Band 2. A different watch, the Polar H7, was used as the standard for judging. The two groups were asked to use indoor equipment to complete activities ranging from sedentary to moderately active.

The watches were found to have acceptable accuracy across the board. The Garmin watch had an accuracy of about 96% for young adults and 95% for older adults while the Xiaomi watch had an accuracy of about 93% for young adults and 94% for older adults. There’s still some room to improve though, especially in terms of eliminating extreme readings.

Still, for casual users, heart rate monitors on GPS watches should be accurate enough. As technology further improves, we’ll only see these devices becoming more and more accurate.

Wrist-Based Monitors vs. Chest Strap Monitors

Now we know that heart rate monitors on GPS watches are accurate enough for most users. Great! But how well do they fare against the older, more traditional chest strap monitors?

Before we discuss that, let’s talk about how accurate chest strap monitors are in the first place.

Chest strap monitors use electrocardiography (ECG) technology to detect heart rate. Unlike wrist-based watches that indirectly measure heart rate by looking at the changes in the blood volume on your skin, chest straps look at the electrical activity of your cardiac area. As a result, studies such as Gillinov et al. (2017) and Wang, Blackburn, and Desai (2017) reveal that chest strap monitors are almost as accurate as an electrocardiogram.

So, how do wrist-based monitors compare?

As mentioned in the previous section, wrist-based heart rate monitors still can’t compete with chest strap monitors in terms of accuracy. One study from the Journal of Sports Science tested two smartwatches, an Apple Watch with ECG and a Fitbit Charge HR2, against an electrocardiogram for a variety of exercises and intensities.

According to the findings, the more intense the exercise, the less accurate the measurements became. This is unlike chest strap monitors, which remain accurate despite the intensity of the exercise.

Lastly, a study comparing the Polar H7 Chest Strap to wrist watches like the Apple Watch Series 3 and the Fitbit Iconic showed that the Polar H7 is still more accurate than any of the wristwatches. The difference in accuracy between the Polar H7 and the Apple Watch 3 is just 2% though.

Nevertheless, if you’re a professional athlete, you would want to have the most accurate measures available for your purposes, whether that’s to detect trends over time or the consistency of your measurements.

Unless you want to go for the traditional chest strap monitor, you should opt for accurate watches such as the Apple Watch Series 6, the Garmin Forerunner 945, or the Fitbit Charge 3. If accuracy doesn’t matter so much as general monitoring performance, you should check out our list of running watches for runners.

Heart Rate Monitors on GPS Watch

A heart rate monitor on a GPS watch is a new piece of technology that has become very popular today.

Not only do GPS watches offer a wide range of other features, they’re also a great way to keep track of your heart rate without the inconvenience of the chest strap.