Preface
I am by no means a running or kinesiology expert. I have done zero research into the matter. The following is just my personal thoughts really on what separates advanced and less advanced runners whether they know it or not .
Running is about efficiency
In my opinion, running is about efficiency. It's about optimizing technique so as much energy is transferred from running stride to running stride. Of course running is an act of physical exertion that takes a great deal of physical endurance. But the majority of progression in performance is due to improving running form in my opinion, because this increases efficiency.
A good question to ask oneself is why with the same amount of physical effort, one can go so much faster longer (while technically moving more mass) if riding a bike compared to running. The answer is that when you expend energy pushing down on bike a pedal, the vast majority of that energy is conserved as you roll forward. The only energy loss is a little friction in the bike's mechanism and wind resistance. You can keep rolling forward until this energy is slowly completely gone.
While running, one exerts energy to push themselves off the ground with each stride. To keep this kinetic energy up between strides on needs to exert a lot of energy to take the next stride . It's hard to really quantify exactly how this energy is lost between strides. But it can be chalked up to a combination of up-down movement, movement of the arms and legs, wind resistance, and maybe some other factors.
So when running your goal really is to transfer as much energy from your previous stride to your next stride as you possible can. By using all your effort to maintain forward momentum. If one expends less energy per stride, to maintain a given velocity that means a lower strain on the cardiovascular system. Which means you can run longer and faster.
So in my personal opinion, the majority of physical improvement that boosts one's running performance are really one's actual running technique developed through muscle memory. This as well as your joints, small muscles, bones becoming stronger due to the uncountable times you've taken a running stride, and the muscular development in your leg muscles that allow them to propel you better.
Closing Words
It may be hard to believe. But from personal experience, focusing/meditating on efficiency while running really helps. Don't try to expend the most energy you can, running as fast as you can. Try to run at a given speed, while expending the least amount of energy possible by transferring energy from stride to stride. All the energy you expend should be towards maintaining your forward momentum.