[misev]

Coincidentally I have the Oura ring too, and my sleep HRV oscilates around 100ms; haven't compared with a strap in the morning though. Strange that you get such low values, maybe something faulty with the ring, or finger placement? It's possible also that the absolute values are not extremely accurate, but the relative trends are. Garmin for example requires a strap to measure HRV stress, even though the watch has an optical HR sensor, which leads me to think optical sensors are not so precise.

What an amazing improvement to 4:30 pace at 140 bpm btw! I've had a similar relative improvement over the first year when I think about it, from around 7:00 to 5:20-5:30 at 140 bpm. But my training was mostly 1km intervals at high end of zone 3 (still quite below threshold), translating to a lot of tempo running on average, plus one session of 200s or 400s faster intervals per week. Been stuck with little progress for a while though, and was thinking to try a more polarized approach like yours with higher volume; thanks for explaining it!