eojtic,
In the indoor season I had a lot more control over my training as indoor track was not emphasized by my coach. As far as finding this information....I was definitely familiar with Lydiard and attempted to run bigger miles than I ever had in the past. What I found was that I was simply uncomfortable running more than 30-40 minutes honestly. I was a wheezing machine and I didn't know what to do. I had good mile and 800m PRs but not great and I always faltered above the 1mile distance.
So what did I do? I consulted other resources. I googled....Hicham el Guerrouj training and found what may or may have been a skeleton of el G's training. I think the link can still be found now through google.
I saw that supplemental training (core exercises, leg strengthening>for muscular endurance) was highly emphasized. When I say core and leg strength I do not mean a 15 minute core circuit at the end of a run as is popular in the U.S. The session I created combined exercises from here and there. I wanted each muscle group to be worked out with what I saw as the most conducive and effective exercise.
Like El G, I would strength train 3 times a week. I found that within two weeks all of a sudden my distance runs were so much more comfortable. I felt as if I "had something" in my legs. It's difficult to explain but for me I felt like I had achieved running enlightenment. I could finally run big mileage and I knew that I was getting far more fit than I had ever been in the past quickly.
I rolled out to the first indoor meet of the season. The year before I had finished 3rd at our state meet in the 1600. It was the first time I felt truly confident going into a race. Something about being able to comfortably run for 90 minutes makes you extremely confident. I had also begun to some 60m or so hill sprints after runs as I had seen a youtube video of some kenyans doing them. It just made sense.
Basically I won by 80 or so meters (low key meet) and ran about a second off my time from the previous years outdoor state meet.
I plateued during outdoors with all the 400 meter repeats and incessant "speed work."