Again the argument about high or low mileage ?
We must decide about what we are talking.
Is the final target to improve their performance for runners of 3 hours or slower ? Or this is an ABSOLUTE problem ?
In the first case, may be that, during the first period of 3 months for beginners, THE MOST IMPORTANT TRAINING is not to increase mileage (soon is possible to run VERY SLOWLY 25 miles a week), but TO QUALIFY the speed. Of course, if I run at a speed of 10:00 per Mile, the first aim is to run at 9:00, in other case I'm a walker.
But, after reaching a good level of speed, I have to move to longer distance and longer mileage.
In the second case, I can explain that, WITHOUT RUNNING OVER 120 MILES a week, it's not possible to be e TOP COMPETITIVE ATHLETE.
I had in my career more than 30 athletes under 2:10, and, like women, athletes (not only Kenyans) running 2:23:47 (Viceconte, 2000), winning bronze medal in World Championships (Ferrara, 1995), silver medal in European Ch. (Curatolo, 1994) and a lot of Kenyans under 2:30.
In all these cases, they improved increasing mileage, and inside the mileage increasing SPECIFIC SPEED ENDURANCE.
For example, I tell you a workouts that Ornella Ferrara did in 1995 in Predazzo, one month before the bronze medal in WCh (that is in my book from IAAF : Marathon, a scientific approach) :
Morning : 4 km warm-up + 24 km at 3:36 pace
Afternoon : 4 km warm-up + 24 km at 3:33 pace
This means 48 km at SPECIFIC MARATHON SPEED in the same day, and 56 km in the day.
So, it's completely wrong to tell to people that you can improve in Marathon using a low mileage.
The reasearch about we are speaking is completely useless, regarding a champion not significant.
For having a correct idea, scientists must invetsigate in groups of top runners, putting everyone in relation with himself and not with the others. In this case, you can see without any doubt that the key is THE INCREASE OF MILEAGE AT SPECIFIC MARATHON PACE.
The problem is : HOW IS POSSIBLE TO INCREASE IT ?
So, we must work in both directions : increasing mileage gradually, and at the same time increasing speed connected with the Marathon Pace. In a period of 3-4 months, we can QUALIFY our long run (running faster), and our speed (running longer). At the end of this process, we are able to build the SPECIFIC ENDURANCE, depending on speed and endurance in same percentage.
What is the endurance ? Of course, nothing to do with a generical mileage at very low pace. This is GENERAL RESISTANCE, and for qualified athletes has nothing to do with the specifity of the Marathon.
But, in any case, don't think that is possible to improve, when you are already at good level, without reaching a mileage of 120/150 miles a week. Only after this, according to the type of athlete that you are (fast of resistant) you can find the best personal key :
RUNNING FASTER maintaining the same mileage, or
INCREASING MILEAGE maintaining the same speed.
Every result, every research out of this rule, is a FALSE research, from scientists that don't know anything about the methodology of training and what training can provoke in your body.
Normally, the research is very good, but the animal is wrong.