I’ve been tracking HRV for about 2 years. HRV value should not be seen as the body answer to just your previous training session. There are 60 – 120 minutes of training and plenty of stressors and inputs over the remaining 22 hours.
Lower HRV doesn’t necessary means your body has not recovered yet from the previous training. There might be other factors causing your lowered HRV. Training on a day with lower HRV doesn’t mean you get unproductive or over trained. Better look at trends, if it stays below average for couple days then you know something is off and some change in regime is needed.
Most of the HRV apps rely on single measurement and that’s also how most of the studies focusing on HRV have been done. There is no benefit measuring HRV during an activity or 24/7. You want to measure it at rest. When I measured my HRV in the morning laying in the bed, the results were almost always green (low resting HR and parasympathetic saturation). Doing the same measurement in standing position gave me more precise results. That’s why I would be skeptical to over night HRV measurements in products like Whoop or Oura Ring.
I switched to FR945 last fall. Watches have some FirstBeat feature called Body battery. I didn’t pay much attention to it but it tries to quantify how much rest you get over night or whilst resting. I had found low values corresponded with nights when I was sick.
I personally think if one pays attention to health (don’t train when sick or tired) and follows well structured training plan those recovery tools and measurements are not necessary. Those apps can be good to predict incoming illness or give you a warning of too stressful time overall. In the end it’s the training plan and execution of work and recovery that makes you faster not the chasing of higher HRV or other metrics.