These are very insightful questions and I'd be happy to answer in detail. If others here care to explain the why/how, I'm also very interested!
It's true that I ran slower on my easy days, and even on some workouts than I did in the past.
What I did differently is what was suggested early in this thread:
- weeks or even MONTHS of easy, slow running to build mileage to 60 mpw
- key was consistency, I had long periods of running at least 1 hour a day in singles. For me, 1 hr is 6.5 miles. When I first built to 60 miles in a week my longest run that week was 10.5 mi, so all of them were in the 6.5-10.5 range.
- I felt very slow, particularly in the summer. We're talking 9:00-10:00 min/mi or even slower.
- I had to keep the faith. I wondered to myself, why am I so slow? How can this make me run faster?
I think the key is that running slow but everyday helped build the musculoskeletal component of running as well as the aerobic endurance and ability to turn fat into fuel, particularly when running on empty (I nearly always do) and with just water. It's easier to get "fit" (i.e. quick) but it takes a long time to build mitochondria and injury resistance.
On workout days though, magically it'd seem that things would fall into place and I was able to complete the workouts without too much strain.
Once the buildup was finished (June-July-August), I started reintroducing some faster pace workouts but WITHOUT adding more miles. I think adding mileage and intensity at the same time is where people go wrong.
I did not have a major setback in this cycle (first time this ever happen) but I dealt often with niggles and small issues.
So what I did is make sure is remain flexible. In September-October I built my long run from 14-15 mi (i.e. 2 hours) to 16, 17, 18 and after that last one, I started having troubles with glutes, quads, hip flexors, so I took advantage of a work trip to Europe to schedule two down weeks with mileage of 50 and LR of "only" 14-15 easy. After this, I did my final two weeks of 60-65 and LR of 19 and 20.
I guess what I am saying here is to remain flexible and avoid any set schedule, so that you minimize the risk of going over the line. I also bagged "T pace" workouts when not feeling alright, or kept them shorter.
All along I knew the key was to make it to the starting line without injury and that any one key workout was not a make or break.
Very true. In particular my easy pace did not change much, I would say 8:30 min/mi on a good day, and 9:30-9:45 min/mi on a bad day. Particularly my first mile on any run...
What changed a lot is heart rate at any pace. I did my recovery runs at HR 115-120 (I forced myself to run that slow), easy runs at HR 125-135 and that was all. Only my M-pace runs (HR 153-163) and T-pace runs (HR 169) went above that.
In the end, running at any pace felt much, much easier, and faster as well, but I did not see any true improvement until the taper. 3 weeks out I did 10E+10M, and the last 10 miles @ 6:50 averaged HR 160-163 or so, that's when I worried that it was too high (= too hard), but during taper 2 weeks out I ran 10E+5M and the last 5 miles @ 6:45 averaged HR 158, and I knew something good was coming up.
On race day I ran the vast majority of miles in the 6:39-6:46 range and it felt very easy, to a point where I almost felt "guilt" for not running harder --- a thought I quickly dismissed telling myself "there's still a long way to go don't be an idiot".
If one sentence sums it up: I became aerobic, smoother and "fuel-efficient" at this pace and that's what got me to 26.2 feeling good.
It's what I needed to break 3, period. With a 37:59 10k and 1:23:59 half, I needed to do the training necessary to "convert".
So what does this mean for my 10k and half pace now? Well at the end of the taper, I ran 3 x 1 mi w/ 1' rest at 6:09, 5:59, 5:58 and had to really hold back on the last reps. I think my LT improved by about 10 seconds / mile, and that running slightly below LT became more efficient/enjoyable. Mile 26 of the race was 6:21 at HR 162 for example.
And in the 10k...that's also a good question. The whole training cycle I wondered why I felt so slow, but once tapered, running faster than 6:00 became possible. The last 0.43 mi of the marathon I ran 5:52 pace, while 6 months ago a 800 @ 6:00 pace was a "speed workout". So while I have no tested my speed or 10k, I would suspect it improved a bit too.
Essentially the work enabled to translate shorter distance results to the marathon, but invariably you should improve them as you go. I just didn't want to "test" them before the marathon, because it was my sole focus. I may train for 10k/half again in the spring and see what I can do!
I think the "pace remains the same but HR or effort feels easier" has to correlate with just "getting faster" but I hear your true question: is there a difference between the two? Can you improve some "spectrum" more than other? For that last question I think yes --- when we train for 26.2, we must absolutely make marathon pace feels like a jog, while our faster paces aren't as critical to improve. They're just a secondary benefit.
Best of luck to you! The best part about the race, outside of the finishing time, was the feeling of cruising and feeling good, almost on a training run. I had a big smile on my face over the last few miles, knowing that the hard work had paid off, and that's when I let off what I held back and just sped up!
Hope this helps, and interested to hear any other feedback from similar past experiences. This thread is really, really good.