I'm also reminded of Australian coach Steve Bennett in one of his articles at oztrack.com regarding the three stages of an athlete. Just a quick summary from memory below:
Stage 1 is the novice, with underdeveloped core stability and strength. So,less overall running and workout volume is prescribed. Also very little long reps, focusing more on shorter fast reps to teach proper movement patterns and hold good form throughout sessions. Main focus is core strength and coordination, plus shorter race distances.
Stage 2 is more advanced and the runners can do longer more volumnous sessions like 6x1000m or 4x1200m, bec they have more developed core. They can hold proper form thro out the longer reps and runs. They can also do more lactic work and run higher overall mileage without falling apart. But core work is still an emphasis as they still exhibit some glaring deficiencies. Mostly national level runners and many world class elites fall into this category.
Stage 3 is the 'super elite' (my term). Good eg is Hicham El Guerrouj ahd Haile Gebrselassie, who r capable of doing sesions like 5x2000m and 3x3000m at or close to 3-5k race pace during base building, and not be overtrained or lose form! They have fully developed or near fully developed core strength and stability and so can handle high volumes and very high levels of anaerobic training, and not fall apart. Usually we r talking abt world record holders here.
(I'm not saying that Bennett's way is the only way to look at levels of athletic competency, just using this as a general skeleton for discussion)
Very often we train way beyond our current levels and/or talent and this leads to muscular and neural shut-down. A lot of stage 1 athletes, who haven't taken the time to build a solid foundation, launches into frequent anaerobic work and high volumes like those in stages 2 or 3. Many stage 2 runners r really stage 1 runners training like a stage 3. So we have cases where runners burn out of hit a seemingly unbreachable plateau in performance, bec they have skipped the intermediate and succeeding stages of development.
Some ppl can spend many years as stage 1, even adults, even tho they r ripping up tough long sessions, bec they haven't built a strong base of physical strength and flexibility. So they either get stuck or break down or both. Some only need a few years at each stage before rising to become world beaters.
Usually when we say 'base' or 'foundation' we refer to CARDIOVASCULAR base, and so we tell novice runners to concentrate on slowly upping mileage to that end. But from my experience,developing core strength and coordination is probably even more foundational to mileage or speed, bec they prevent breakdown structurally and improves running form.
I'm not saying that elites do not get hurt, but that they can sustain very much higher levels of work before that happens. Just look at runners like Bernard Lagat & El G at the end of the 2004 Olympic 1500m, how they r holding near effortles looking form even in full sprint for the finish side by side! And under unimaginable pressure! That's not just miles in the legs and lungs but also stability and strength in the torso and glutes.
I'm guessing that many of us here r going thru this perplexing problem bec our bodies r telling us to go back to stage 1 (or 2 for some) and try to pass elementary school before we take on high school, and then high school before we jump to college. Unless u r extraordinarily gifted, u don't get to skip grades. Even a super talent like Hicham El G had to spend his teens developing core strength and coordination before he took on the world. That is how the Moroccan atletic federation develops its runners, from the very basic physical mobility and strength before proceeding to the fast,long and hard running/racing. Nothing is forced before its proper time.
Often I see coaches and runners grade stages of a runner's development in terms of how much mileage they can handle, or how fast they can run a certain distance. While this is not necessarily wrong, but they often fail to see things like core development and cyclomotive coordination, which tell us what level this particular athlete, highly talented or not, is able to SAFELY train at. This oversight, in my opinion, is part of why many promising runners fall into obscurity and fail to reach world-class. They r simply trained way beyond what their bodies can take.
I think its a worth while period we r experiencing now, even as we try to tackle this seemingly bizarre coordination problem. Maybe we shd put off serious racing for a while and take that time and effort to build (or re-build for some) our core, wh of course includes the glutes we have ben talking abt. I believe when we finally overcome this problem, it will lead to higher levels of training and racing, coupled w a wiser mind and humbled heart. But if u rush it u may never come back.