Hi, I just discovered this thread and find it very interesting. I'm male, 56, ran my marathon 2:37 PR at age 32. I've studied exercise phys (was in a PhD program but bailed...) and tried a lot of different types of training on myself. A few points:
1. Great to have Bob Schul's input here.
2. I agree with the comment that there is so much we don't know yet about the physiology of running.
3. I believe it was Peter Snell when he became an exercise physiologist that found that FT fibers were recruited at the end of long runs. I'm not up to date on current thinking in this area.
4. I believe it is hard to separate the training effects of workouts. One might say that Paula Radcliffe's 140 mpw are for maximal aerobic development but there are other possible benefits. Dr. David Martin told me years ago that he thought that level of mileage improved glycogen storage. (Costill's research showed max VO2 gains at 90 mpw). Also while this thread is about aerobic base, there is significant muscular strength improvement that comes from running a high mileage base. I think this is a strength-endurance effect and doesn't get discussed much because folks often focus on aerobics, anaerobics, lactate threshold etc. (Read Tim Noakes on muscle strength).
5. I believe there are strength benefits too from Lydiard's hill springing workouts. Sure they benefit anaerobics but probably also on stride length - improved quad strength, longer contraction of the Achilles and calf muscles perhaps.
6. For myself, I got my best results from running 10-milers at an effort where I never got into heavy breathing (2-3x per week) - so you could say they were primarily aerobic with little lactate accumulation. I also would run my recovery days (maybe still 10 miles) but at as easy a pace as possible. The test in them being easy enough was being able to repeat the fast aerobic run the following day.
7. That being said, I also benefited (half-marathon PR 74:02) by running 10x400 (ave. 68 secs - fast for me!) with a very easy 3 minute jog recovery rather than 12x400 @ 72 sec with a short (100-200m) recovery.
8. So it's all intriguing. I do believe I could have run faster at the marathon if I have done 2-a-days to get 100mpw rather than 80mpw in one per day. I also think I could have run better at 5k and 10k with more fast intervals with long recovery - as Lydiard said, lower the pH and let it recover.
9. We are all different and different people have success with different training methods. But maybe the effects of some seemingly different methods are similar. E.g. Zatopek's huge number of intervals that weren't really that fast with short recoveries might resemble a steady 10-mile aerobic run.
10. Some things seem evident - there don't seem to be many (any?) world class distance runners not running a lot of miles and many of them fast aerobically.
Rick