From a previous thread. Post from Canova:
"In my experience, also athletes not fully professional can have advantage using "Special Blocks". Of course, the intensity and the volume must be related to the other part of training.
So, if an athlete with an average of 30 km per day can use special blocks of 50 or more km, an amateur having an average of 12 km per day can use a Special Block till 30-35 km.
But Special Blocks are not only for Marathon runners.
We had Special Blocks of VOLUME (for example, 10km at 90% of MP + 20 km at MP both in the morning and in the afternoon), MIXED (10 km at 90% of MP + 10 km at 102% of MP in the morning, 10 km at 90% of MP + 12 x 1000m at 105% with 1'30" recovery in the afternoon), or specific for short distances (Special Block for 800m : 30' easy run + 10 x 600m at 87-90% of the speed of 800m with 2' recovery (in the case of a runner 1'44" : pace for 600m is 1'18" (78"), 10% of the time is 7"8, 1'18" + 7"8 = 1'25"8)in the morning, 30' easy run + 4 x 400m at 105% of the speed of the race with 6' / 8' recovery (in the above case, 1'44" pace is 52" for 400m, and 5% is 2"6. So, in this case, 4 x 400m in 49"4 rec. 6').
I saw every athlete growing a lot in his shape after using this type of training.
But the athletes must not do the mistake to arrive to a Special Block tired, and have to recover very well."