Blind Boy, I agree that long
Blind Boy, I agree that long slow running is core for any distance runner and I read Hadds exposition. Full of great knowledge and the guy is talking about super elite athletes. I have been long slow, sub LT, training for years and I only see increases in my speed when I do interval training. It isn't so much that I need to increase LT, My body needs to learn to run fast and if all someone does is run slow then the body will run slow. It takes speed to run fast.
Speed in a mid range run like a 5 or 10k is multifaceted. The body needs to know how to conserve energy for the long haul yet the muscles need to have some semblance of muscle memory of what faster paces feel like. 10 years of running 11 minute miles won't cause a runner to pull off an 18 minute (sub 6) 5K. It just won't happen.
What is most frustrating here is it seems that it always turns into a two sides coin, heads or tails, but there is a place for both sides. Any training regiment without both is bound to fail.
I certainly am no expert but I have done a lot of bike training in the past and used Troy Jacobson's plans. He has a very popular saying that most athletes train to light on their hard days and train to hard on their light days. He is a proponent of both long easy rides/runs and hard intense interval rides/runs. The error I know I make very often is I let ego get the best of me and on long runs I worry about time and on intense days, I often don't push to the point of puking or almost puking.