I understand the idea of going from 50 mi/wk to 80-100 making a huge difference.
But what if you're coming from Triathlon, where you were doing 50 running miles a week, but 15-20 total hours/wk of total aerobic work?
If you go from 20 hours/wk of tri training to say 10 hours/wk of strictly running, but at 80 miles/wk, will you still see improvement? Surely one would see improvements in running economy from all the additional easy miles?
I double a lot, almost every day, and the main point of the 3-4 mile jogs (I run 80mpw) is to enhance recovery and shakeout. The secondary effect is of course getting some aerobic benefit, but the main goal is to feel as fresh as possible for the next day.
There are a lot of things happening besides aerobic benefits.
Your body continues to adapt to the stress and get more efficient at handling it. Your bones, tendons, muscles, etc. continue to change.
You also continue to get better at the skill of running. There is a good chance as a triathlete, your work in other sports limited your ability to be as good a runner as possible. This isn't a value judgement on picking those three activities (I do a lot of other fun things that could be considered hindrances to my running). But, the more miles you do, the better you will get at covering distance and at a faster rate. Some of this will no doubt be aerobic improvement, but much of it will be do to the practice of running.
It's also about building the ability to run a lot of volume. If you are covering 12-15 miles a day, doing 8-12 miles very fast or 13-20 miles moderately fast gets a lot easier. You will see improvement IF you use mileage as a base for more long/fast intensity.
It is neuromuscular pattern "machine learning". Time in to the system leads to greater efficiency of recruitment of different muscle fibers and firing patterns.
Most of the gait patterns (neuromuscular firing patterns) of walking and running are executed at the spinal level and are a simple feedback loop.
Google decerebrated cats experiment.
Good stuff. Appreciate the responses.
Good topic. I was running 50 miles a week and averaging about 20 hours a week triathlon training. Now I just run and have been averaging around 80 miles a week for about 6 months. The training time has gone down dramatically compared to when I was training for triathlon. I have seen improvements in my running and I've got faster. You will probably see a drop in weight which will be greater than you experienced in just triathlon training.