Image source: Garmin

Garmin Forerunner & Apple Watch heart rate accuracy quantified by medical study

A medical study published a few days ago in Digital Health (via Sage Journals), has shown both the Apple Watch and Garmin Forerunner heart rate sensors to be highly accurate, with Apple having a slight edge.

The actual objective of the research was to evaluate the validity of prescribing exercise intensity using wrist-worn devices. This is what separates the study from other similar research efforts. Those were focused mostly on assessing the accuracy, reliability and validity of of commercial heart rate sensor measurements.

Wearables typically utilise target heart rate as a tool for prescribing exercise intensity. That’s because variations in heart rate during exercise are indicative of real-world effort. Wrist devices utilise HRmax to determine heart rate zones and other information that goes into these calculations.

And this was the focus of the scientists. To determine the validity of exercise measurements based on HRmax. The secondary objective was to determine which device was more accurate, the Apple Watch Series 6 or Garmin Forerunner 945.

The other benefit of this study is that it was peer reviewed. This means it was evaluated by people with the same competencies as the producers of work. These methods are often utilized to ensure quality standards.


The study – evaluting against a 12-lead ECG

Some thirty healthy and willing participants were recruited for the study. Their number was split equally between males and females. The participants were instructed to perform formal ramp incremental exercise tests on an electronically braked cycle ergometer equipped with a face mask.

Their heart rate was recorded with three different devices. This includes a 12-lead electrocardiogram as the gold standard, along with the Apple Watch Series 6 on one wrist, and Garmin Forerunner 945 on the other.

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The interval-type tests for individual subjects were terminated when the the subjects were left exhausted by the exercise protocol. Their heart rate was analyzed at both the lower and upper limits during the workout. Resting values were obtained from the average heart rate measured during resting phases. HRmax was defined as the highest heart rate a person achieved throughout the entire exercise test. The heart rate zones were derived from this figure.


The results: Apple Watch & Garmin heart rate sensor accuracy quantified

The study demonstrated that both the Apple and Garmin devices showed excellent accuracy as compared to the 12-lead ECG. But the first was slightly better. The report authors speculate this may be due to the sensor technology implemented by the two wearables manufacturers.

The Apple Watch utilizes sensors that combine both green and infrared light-emitting diodes (LED) to detect blood flow in the wrist. Garmin, on the other hand, only uses greed LEDs to track heart rate.

The thing is, while green LEDs are more resistent to motion interference when it comes to such measurements, they have a limited tissue penetration. Authors say the combination of sensors in the Apple watch may result in better noise filtration and a decrease in the error rate.

Nevertheless, the overall error rate on the Garmin Forerunner 945 only ranged between 1.16% and 1.39% for various heart rate zones. The Apple Watch Series 6, on the other hand, ranged between 0.91% and 1%. Researchers note that the Garmin showed a bit less correlation for very vigorous activity as compared to the Apple Watch.

In terms of beats per minute (bmp), the absolute error for the Garmin ranged between 1.35 and 2.25. For Apple the values were between 1.16 and 1.48 across the different intensities.

This is all the more impresive when you take into consideration that both of these are older generation devices. Apple is now up to Series 8, and the Garmin Forerunner 955 saw the light of day a couple of months ago. Both of these have next generation heart rate sensors.

The authors conclude that both Garmin and Apple devices can be used for exercise prescription based on heart rate. They do, however, suggest that future research should be done on this subject to include other population cohorts. This includes elite ahtletes, the elderly and others which may not have been adequately represented in this study’s participant sample.

For more detailed information on this research paper head over to Digital Health (via Sage Journals).

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