Early research had some issues
Garmin wasn’t shown in a very good light when it first appeared in a research paper from 2022 with its Forerunner 245. The study showed a very poor 24 % accuracy when it comes to HRV which is especially terrible compared to Whoop that excelled with a 99 % accuracy.
The problem is that the study was mainly focused on evaluating sleep tracking and HRV was only a secondary metric in the experiment. All of the other devices tested in the study (Apple Watch S6, Polar Vantage V, Oura Ring Generation 2, WHOOP 3.0, Somfit) were allowed to collect the HRV data overnight. The Garmin Forerunner 245 was the only device that measured HRV only for 3 minutes around 1 hour before sleep. This is a huge problem.
HRV needs to be measured overnight or first thing in the morning to interference by other factors. If you measure HRV in the evening, you could get very inaccurate data if the person had a coffee recently, just ended exercising, had a big meal, is stressed after a busy day, or a number of other reasons. So, this is not a useful way of measuring the HRV accuracy of a device. The Garmin wasn’t really given a fair chance here.
A fair trial for Garmin
It seemed suspect that Garmin would be so far behind the competition when it comes to HRV, especially considering the results of a meta-analysis from the same year that evaluated 23 studies on the topic. It concluded that portable devices only have a small amount of absolute error when compared to the gold-standard electrocardiography (ECG).
In 2023, there was a new study that included a different Garmin device. It was the Garmin Vivoactive 4 which came out in 2019, just like the Forerunner 245. The study focused on participants with a history of heart issues. The watch was worn by 104 people who have previously suffered from a heart attack, 129 ischemic stroke patients and 30 healthy people as a control. The participants were connected to an ECG machine for 30 minutes with the Garmin monitoring HRV at the same time.
Garmin’s HRV measurements offer excellent accuracy compared to an ECG
The study showed that mean heart rate and very low-frequency power, both used as indicators to determine HRV, as well as the standard deviation averages in 5-minute segments were found to be very comparable to the gold-standard, ECG. In other words, Garmin is very accurate and there is good reason to have faith in the HRV numbers it produces.
It’s also worth noting that this was a 2019 device that was included in the study. Since then, Garmin released new devices with improved optical sensors and no doubt improved their software too. This is good news because HRV is a key metric helping Garmin offer deeper insights about stress and training readiness.
