How Oura, Whoop, and Garmin Compare on Measuring HRV

Heart rate variability is an excellent metric for measuring how much stress your body is under. Many wearables can record your HRV overnight and give you the data in the morning, alongside your resting heart rate, another useful number. But which device does that best? I wore three different devices to bed for three weeks to see how they compare, and the results were surprising. 

The devices I tested were an Oura ring (gen 3), a Whoop 4.0 band and a Garmin Forerunner 265 smartwatch. (Full review of the Forerunner coming soon...