The modern preparation for the marathon doesn't affect the performances on track, if the coach understands HOW and WHEN to put specific training for long speed endurance.
Paula Radcliffe bettered her PB in 3000m of 6" AFTER running her first London Marathon. Last year, Wilson Kiprop ran Prague Marathon on 9th of May, and AFTER bettered the WR of 10000m in altitude of 18", won African Champs in 10000m beating Kipsiro in the last lap (arguable one of the best finisseur in the circuit), and became World Champion in HM, when was 23 years old.
So, the problem is different. An athlete, or has the attitude for becoming a top marathon runner, or doesn't have. In the first case, it's useless and damageous to stay long time on shorter distances, waiting that the body is no more able to have the full efficiency before moving to marathon. In the second case, NEVER the athlete can become a top marathon runner, since the main quality for running a fast marathon is not to be old, simply....
Of course, if we speak about a preparation based on the EXTENSION OF THE INTENSITY, we need to start from the intensity, and this is possible only when the athletes are still in their growing period. Instead, if you look at the "classic" preparation for marathon runners old style, based on a lot of mileage at low and medium speed, you can see athletes losing their speed in short time.
It's obvious that, if we want to reach our top in a marathon, we can't do this when no more able to run fast in shortest distances.
In Boston, the second half was at a pace of 2'52"8. Do you think possible to do this, if at the moment the athletes are not able running 27' in 10000m ?
All the athletes having a long career in 5000 / 10000m (including Gebre and Paul Tergat) were not able to reach the level can reach starting the preparation for marathon when still able producing their top results on track. Gebre maintained his speed a little more than Tergat (he ran 26'50" without specific preparation, only 28" slower than his PB, also many years later), but Paul lost between 50" and 1', so the Tergat marathon runner was not the real Tergat, but his elder brother.
The question is : Which results in Marathon Gebre and Tergat should had reach, if moving to the distance 5-6 years before ? And this type of preparation, how much could had affected their performances on track ?
In my idea of training, athletes as Moses Mosop, Wilson Kiprop, Sammy Kitwara, Florence Kiplagat, Mary Keitany and some other still young, moving to marathon now, can continue to improve their value for 10000m, and to maintain their value in 5000m.
The problem is the calendar. Looking at two marathon per year, we need a period of preparation of about 3 months, without resting too much after the first seasonal marathon. This means, for example, that after a top marathon about the end of April, we have one month easy, one month for recalling all the fundamental types of training, based on the increase of the aerobic power, and 3 months specific, with the goal to extend the duration at the intensity of the marathon.
Nothing to do with the marathon of 30/40 years ago, the marathon of Rodgers, Shorter, Bob Hodge, a marathon for running 2:10. Now, we speak about two seasonal marathon at 100% of the preparation and of the level. This means more precision in recovering and in rebuilding what you lost during the specific period of training for the previous marathon, more concentration, and we can't be competitive in shorter distances on track at top level.
Different is the fact to skip, every 2 years, one marathon, for having a period of 3-4 months dedicated to the track, in order to enhance the speed. This is part of a technical project, and has nothing to do with the pleasure to run on track.
The difference between the mental formulation of a season "old style" and "modern style" is in a more accurate approach in training, while 40 years ago the main motivation was the joy of competing.
Under this point of view, we need to teach the marathon runners HOW to train without competing too much, but also HOW to compete without training, only.