HRV Comparison: Oura vs WHOOP

Every week, we are comparing wearables and sensors. For this week, we are continuing our comparisons on HRV, with WHOOP and Oura.

We discussed Oura's HRV readings during sleep when we compared it to the Polar Unite (check that out here). The Oura ring performed much better at measuring HRV in our last comparison. While HRV is a sensitive metric and some volatility is to be expected, Oura did not have as many spikes in its readings. The Oura ring records HRV every 5 minutes during sleep.

In terms of WHOOP, while it measures HRV throughout a sleep session, only the average HRV for the session is recorded. As a result, to compare Oura and WHOOP, we have to look at HRV averages/night for the entire week instead of HRV samples taken during a single night. A graph of Oura and WHOOP's HRV averages during sleep can be seen below.

The average HRV readings here are quite interesting. While we miss out on the fine grain detail of how our team member's HRV fluctuates every few minutes, we can still see the overall trend of their HRV throughout the week.

The trends from both devices follow each other well. WHOOP's HRV is however 5ms–10ms higher on average than Oura's readings. Both devices showcase a decrease and subsequent increase in HRV between August 31st and September 1st. Oura's HRV then remains fairly constant from September 1st - 4th, while WHOOP's HRV readings drop and then increase in that time. Interestingly, the steady increase in HRV beginning on September 3rd for Whoop and on September 4th for Oura coincides with the weekend. The highest HRV recorded for both devices was on September 5th, which is Monday morning. For the rest of that work week, Oura and Whoop both measured a consistent decrease in HRV. Clearly, our Terra team member had a relaxing weekend followed by a pretty stressful work week right after!

The trend for average HRV readings also appears less volatile than for HRV readings taken throughout the night. The effect of averaging the HRV clearly smoothes out the volatility as opposed to the actual readings themselves being less volatile. This can be seen if we take a look at the graph below showcasing the HRV sample readings from Oura for one of these nights as with previous HRV comparison articles.

While other devices spike a lot more than Oura (and Oura tends to measure HRV at a lower magnitude than other wearables), there are still some spikes and volatility in the graph above for HRV readings taken during a single night, as we saw in previous HRV comparisons. The HRV increase toward the end of the night at around 5:30 AM is likely due to quality sleep and the body undergoing repair, especially since WHOOP also records an HRV increase for this day as we discussed. However, because WHOOP only records HRV averages, it's not possible to make conclusions about which wearable has greater volatility in their HRV readings.

Due to the known issues with measuring HRV, it's still difficult to blindly trust HRV trends recorded from a single wearable. However, we can make interesting conclusions when multiple devices' HRV readings match, such as for the increase in our team member's HRV over the weekend. If you have multiple wearables measuring your HRV and their trends match, this is a pretty strong indication that the trend is reflective of actual lifestyle choices. Whether this only applies when looking at average HRV data or if this also holds true for minute-by-minute HRV trends needs more looking into. Nobody wants to have to purchase two wearables just to verify the validity of their HRV trends, but sensors and HRV measurement techniques are only going to get better with time.