Partially inspired by this thread, I decided to do a weekly 10k time trial every Friday since March because all races are cancelled and I'm not training for anything. Right now is a good time to experiment with some stupid training. Background: I'm 30, my PR is 33:06, and I was in around ~34:00 shape coming off a 16:10 5k in early March. I'm much better in races than in TTs.
So far, I've gone: 34:40, 34:31, 34:42, 34:23, 36:05 (major blowup), 35:24, 34:55, 35:40 (super hot), and 34:48 today.
Lessons learned:
1. The 10k whips you into shape pretty good, and you're getting a lot of time in the right HRZ doing this. It's well documented that CV pace is good for sharpening, especially coming off a base period.
2. I finished every effort knowing I could have gone faster in a real race.
3. The first 5 weeks I was super motivated to beat my previous week's time and I was making some minor gains. It was fun, but also really dependent on conditions. After blowing up in week 5 by going out too hard, I experimented by going out easy in the next couple. The last one definitely felt easier than the first one, so overall I may have had some adaptions to this training stimulus. But to be honest, I think my effort level depreciated over time to something slightly slower than 10k pace. It's really freaking hard to push yourself for a long TT. I have no idea how people are running full marathons at max effort without being in a race.
4. A 10k TT tests your mental strength more than anything. I wanted to quit in mile 4 every time. Unless you can somehow build up the TT in your head to think of it like a race, matching real race effort is super tough, and nearly impossible to do every week. If OP is telling the truth, I think his extreme progression may be from building the necessary mental fortitude to reach fitness he already had.
5. I was feeling major metabolic burn in the following 36 hours of doing one of these. Harder long tempos are good for dropping weight.
6. I'm itching to get back to short intervals. After this, I honestly can't wait to run 400 repeats again. It's good to mix things up.