Here you have some of the training the best runners are doing, impressive.
If you wonder how a marathon runner can run fast shorter distances you can get you answer from one of the best running coaches, Renato Canova. http://www.letsrun.com/
http://www.letsrun.com/forum/flat_read.php?thread=3923991#3925132
In our case, speaking about athletes preparing marathon but ready for a cross 4-6 weeks before, we have 3 kinds of speed endurance :
A) Specific “Marathon Speed Endurance”
Examples :
- 5 times 5 km in 14’45" / 15’ alternated with 1 km in 3’40"
- 7 times 3 km in 8’45" rec. 600m in 2’30" / 3’
B) Specific “10000m speed endurance”
Examples :
- 4 x 2000m in 5’25" + 1 x 1000m in 2’35" (rec. 4’ jogging)
- 3 x 3000m in 8’20" (rec. 4’) + 10 x 600 in 1’33" (rec. 1’)
c) Special Blocks (special training morning and afternoon)
Examples :
1 - Morning : 10 km at 3’15" (32’30") + 15 km at 3’04" (46’)
2 - Afternoon : 10 km in 32’30" + 12 x 1000m (track) in 2’42" (rec. 1’30") or 6 x 2000m in 5’35" (rec. 2’30")
With this type of training, the athletes maintain the speed they need for running 12 km, having at the same time more endurance.
Don’t forget that both Wilson Kiprop and Geoffrey Mutai, last year, went for 30 km in 1:36:30 exactly five days before running in National Champs 27’26" and 27’27".
And, speaking about the past, that Paula Radcliffe improved her PB in 3000m (from 8’28" to 8’22") in 2002, in her first competition after London Marathon (2:18).
So, instead fearing the volume for preparing Marathon, it’s better to find stimula from mileage at high speed, if athletes want to improve their PB in 10000m (and also 5000, with only some small difference).