HR comparison during sleep: Oura vs Polar:
TL;DR:
- Polar Unite heart rate (HR) data spikes a lot more than the Oura Ring 3.
- Polar starts recording sleep later than Oura in some cases
- For the most part, Oura tends to notice changes in HR trends earlier than Polar
- In one case where the Oura Ring data spikes down, Polar HR shoots up (April 14th 6:15am), Polar eventually catches up at 7:00AM
- Sometimes the Oura Ring does not record HR trends that the Polar Unite does. Is Polar right or is it bad data?
- When Polar HR spikes it eventually comes back down to match Oura's HR readings shortly after, indicating Oura's readings were probably the correct one vs. the Polar HR spikes
- In general: Oura picks up changes in HR earlier than Polar, Oura starts recording sleep earlier at times, and Polar has a greater variation in HR
A lot of people are asking about the accuracy of wearable devices, and thus we wanted to shed some light on this. We got two wearables, an Oura Ring 3, and a Polar Unite, and put them to the test.
The Oura Ring 3 and the Polar Unite promise to provide accurate, continuous heart rate tracking during sleep. Both wearables utilize an optical heart rate sensor, with Oura promising a 99.6% accuracy. One of our Terra engineers, wore both devices for a week and recorded his sleep. We then ran a script to visualize the resulting heart rate from Polar and Oura overlaid onto one another. An example of this data can be seen below.
In general, both Polar and Oura pick up the sleep session and in a bigger picture sense we can see from both wearables resting heart rate is quite high here, without much time in deep sleep. However, when we look more closely at the data (e.g. 15 minute intervals), there are clearly some inconsistencies between the Polar and Oura HR data and their ability to keep up consistent measurements and pick up changes in HR. We can see that the Polar has a larger variation in heart rate than Oura for smaller time intervals, with spikes occurring more frequently for Polar.
A repeating trend that occurred most days is that Polar has greater variability and unexplained HR spikes in its data and that Oura can pick up changes in HR before Polar does (as well as detect when falling asleep sooner than Polar).
Spikes and Lags
Looking at the above data, we can see the greater HR variation from Polar than Oura, especially the erroneous spike occurring at 2:30AM which Oura does not pick up. Given the high sampling rate and accuracy of the Oura Ring, as well as the repeated trends in most of the data, we can conclude that these spikes are not indicative of actual HR spikes the user is experiencing during sleep. While there are some cases where the Oura Ring spikes in HR, such as at 3:30AM, these spikes or dips are always tamer than the variation for the Polar Unite.
At around 4:00AM, the Polar Unite begins to closely match the Oura Ring's trends. However, from this time until the user wakes up, we can see how the Polar data lags behind the Oura Ring in terms of picking up changes in HR. For example, the jump in HR from 67BPM to 71BPM at 5:00AM is picked up slightly later for Polar. This trend repeats in all measurements. At around 7AM, we can see the Oura Ring heart rate begin to increase to 67BPM. The Polar Unite records this trend shortly after but shoots up higher to 71BPM. Dips in heart rate that Oura picks up on first also appear larger for the Polar Unite.
The graph below showcases a scenario where the HR measurements are more erratic for both Oura and Polar.
We can also see here how Oura records that the user is asleep nearly a whole hour before the Polar Unite watch. This night seems to be one of restless sleep, due to the high variation in heart rate for both wearables. However, the Polar Unite still spikes a lot more than the Oura Ring in this case. This graph allows for the conclusion that because Oura is less erratic than Polar even on a bad measurement day, the Polar spikes and greater variation occurring on other days are not indicative of actual HR changes that a user should worry about.
