The root question seems to be, "How do I improve my easy run HR?" And I'm not positive of the answer, but I'd say your easy run HR is when you're running and it feels nearly effortless. Like you're literally barely trying. That's how I would personally describe EA pace (see below). So I'm not sure I ever improved the HR at which it feels effortless, but rather the pace at which it occurred has gotten faster.
My preferred method is Heart Rate Reserve which takes into account both the maxHR and restingHR.
View attachment 469410
View attachment 469411
I used a lower restingHR and higher restingHR to give a sort of range of values to see. Essentially, it would appear your "easy" zone would be around 150 or less. So that's higher than either of the two values you had.
Personally though, I prefer to use HR as a secondary measure of training. It's something I look at post-run to monitor the changes in the HRvPace relationship. It's important to remember that HR does not exist in a vacuum when it comes to pace. The HRvPace relationship can change based on the weather, the elevation profile of the run, stress, etc. With that being said, looking at in a zoomed-out perspective can allow you to see the bigger changes.
View attachment 469415
View attachment 469414
Two graphs showing the pace at which I can run at a certain HR changing on a bi-weekly basis or from year to year. These improvements come in line with an ability to run faster races. Both of these graphs were made with data where I did my best to control for variables other than HR and Pace.
I prefer to use effort and current fitness pacing as my gold standards for training around. So of the 4 PRs in your signature, the HM is the best from an equivalency standpoint. So I'd choose pacing based on that. Admittedly though, it's unusual to see a HM PR that betters a 5k/10k PR unless there's been a significant amount of time since the 5k/10k races.
View attachment 469417
The HM PR would suggest a training methodology that tends to average around a 9:45 min/mile and about 80% of training at 9:29 min/mile or slower. So then the follow-up question would be, should/could I train slower than Easy #1 (10:26)? According to Tom Schwartz's data (which he has not made publicly available), he claims that you can train as slow as +5 min from 5k pace and still reap the benefits from easy/recovery running. So that would be something like a 12:40 min/mile is still within reason for a nice and slow easy run. At the end of the day, I usually say "Don't go faster than EA (or EB), but you're absolutely welcome to go slower." And there are plenty of conditions, like super hot days or running up a hill, where I'd recommend to go far slower than even the paces above.
I think a training plan that balances both the slow easy/recovery end with the faster end usually leads to a good cycle over cycle return. A dichotomous training plan that becomes specific once the race gets closer. So the further out from the HM the more you should be working on 1 mile, 3k, 5k and super easy pacing. Then as the HM gets closer, you focus on LT, HM, and LR pacing.
Lastly, your goal is a 1:45 HM. That's a 4% improvement from where you are now. That's not an unreasonable gain to see in a single cycle, or maybe two cycles. It depends on how long you've been training for and how different what you've done will be from what you do next. Additionally, not all races are created equal. It would be somewhat unreasonable to expect a massive improvement if say the HM PR of 1:49 was set on a downhill course that had nice cool temps and a tail wind VS when an "A" race comes up that's super hilly and like a billion degrees. The conditions of race day will certainly impact the ability to "see gains". That's where we circle back and look at the HRvPace data and possibly can interpret that information to show that gains were made even though maybe that single race day didn't have the outcome desired.
If you want to know if you've maxed out your speed, then I've got a simple run test. Run a mile faster than 6:47. If you can, or have, then your PRs will drop further when you have the endurance to match. A different workout that tends to be a good indicator for me to watch for is something with 200m or 400m intervals at not all out sprint, but a very hard consistent effort. How does that then compare to a 6:47 min/mile pace? When I see someone generally outperform their 1 mile runs or their 3k runs, that's when I have a good idea as to how much further they can go just by improving their endurance.
As for rate of gains, this is my graph for HM and M performance over the last nearly 8 years, 11,000 running miles, and 7,000 indoor cycling miles. I'd say for me personally, the game changing moments were Hansons marathon training in Fall 2015 and Daniels 10k training in Spring 2017. Those are when I saw the highest rate of return/biggest gains from the prior training cycle.
View attachment 469463
