Interesting that you mention sleep HRV. I use the Oura ring and have observed that my sleep HRV is super super low at the moment, like 15/20ms but when I check it in the morning with my polar H10 strap then it will usually come out between 60-80ms. Tried to figure out what causes it but not had any luck so far. I don't think I'm over-training or have any other issues.
I follow Phil Maffetone's training methodology [1], which has worked quite well for me. So currently, 80% of my training by distance/time is between 135bpm and 145bpm. The training is mostly steady runs between 7km to 25km. The remaining 20% is a mixture of progression runs, speed training, and intervals.
Initially, for the first 6 months of training, all my training was below 145 bpm and was quite slow at 6min/km but now I can do 4.30min/km at 140bpm and I'm still getting faster!
Cheers
