1) Yes, of course my pace at 140 HR (77% max) increased. But I'm also producing significantly less lactate at any HR. My lactate at 145 HR is still extremely low now and much lower than it used to be at 140 HR in the past when I wasn't well trained.
Look at this graph, which shows 4 lactate tests (protocol was 5x1600 in the first three and 5x2000 in the last):
https://i.imgur.com/IPnfjpR.pngDecember 2017 - black
April 2018 - green
June 2018 - blue
March 2019 - red
All tests were done on a 200m indoor track with same temperature and conditions.
What can you see?
a) My pace at 140 HR is always increasing.
b) I did not improve much from April-June 2018. During this time, I did plenty of hard/all-out intervals (Daniels VO2MAX 1k's) and hard tempo runs. What happened is I got stronger anaerobically, able to go out really fast during races but I did not improve my stamina or race times. This was a learning lesson and I decided to switch to Tinman and trust in the training of my coach which was slow but similar (CV reps instead of VO2MAX 1k's).
c) My lactate at 140 HR was 1.8 in the first test, 1.9 in test 2 & 3, and only 0.9 mmol in test 4. My aerobic system got much stronger due to the CV training, Tinman Tempos and increases in mileage that I'm producing less lactate not just at faster speeds, but also at the same HR.
2) Daniels gives 65-79% for easy runs in his book and online calculator. When my glycogen stores are low, and my legs are fatigued I run at a lower % but my max HR is also much lower during that time. My max HR changes between 170 and 183 depending on conditions, fuel status, hydration status, weather, stress, etc. In November last year I ran an all-out mile at 170 HR (my max at that day) in 4:55, which was my first mile TT ever. Why max HR so low despite all-out effort? It had 15 degrees F, I had an all-out XC race just 2 days prior to it and exam stress in school.
Tinman uses 70-79% for easy runs which takes into consideration the fact that max HR can be lower. Salazar doesn't specifiy a percentage but says that Mo and Galen run their easy runs in the 140s and at a brisk pace (5k+90s/mile) and that it's fine if they don't feel super fresh for each workout. He rather makes the easy runs effective and develop fitness than to do junk miles and be fresh at the workout.
3) My easy runs are (perceived) very easy now, no matter the HR. A 140-145 HR easy run can feel better and easier than a 125 HR easy run when I'm depleted and my legs are trashed. However, I still make mistakes. Sometimes I get rolling on easy runs, especially when there is a hill and I easily run it up with 155-160 HR. While the run is fine and feels easy, the next day tempo run couldn't be completed at the goal pace and was slower than it should have been. I wasted precious glycogen on the easy run the day before which I shouldn't have done.
Tinman's thoughts on it? Check here:
https://www.therunzone.com/viewtopic.php?f=3&t=1075#p4734He states that easy runs can be too fast BUT also be too slow, and 70% for a fast-twitch based runner might be too slow as he would only use ST fibers at that pace which he doesn't have nearly as many as a ST runner.