During the preparation for a marathon athletes have to optimize their "specific marathon speed endurance", that substantially means long and fast run, even paced or using variations (for example, 7k+6k+5k+4k+3k+2k starting with 7k at Marathon Pace and increasing, for every distance, the pace for 2" per km, with 1k of recovery at 80% of MP).
For these reasons, after the race the athletes have less muscle strength and less elasticity/reactivity.
We need to work, during the first 6 weeks after the race, for recruiting these qualities, using circuits, short intervals and gym.
The fact that, if athletes understand the right way of training, from a Marathon is possible to run fast on track, can be confirmed by some excellent example :
a) After running her first marathon in London in 2:18, about 60 days later, Paula Radcliffe, in 2002, destroyed her PB in 3000m running 8'22", after trying in 6 years (1994-2000) to move from 8'31" to 8'28" using a lot of speed.
b) In 2010, Geoffrey Mutai ran under 2:05 in Rotterdam, and Wilson Kiprop in 2:09:09 in Prague (9th May). After, they went to 10000m, running at the end of June (so, for Wilson 47 days later) in 27:26 (Wilson) and 27:27 (Geoffrey) during the National Kenyan Champs, WR in altitude, and one month later Wilson won African Champs in 27'32" with Geoffrey number 3. And, in October, Wilson became the World Champion in HM, and Geoffrey ran in Berlin 2:05 again.
c) In 2000m, my Italian Record Holder, Maura Viceconte, beated the National Record of Marathon winning Vienna (21st May) in 2:23:47, after 3 weeks bettered her PB in 5000m (15:18 from 15:45) during the European Cup, and at the end of July improved the NR of 10000m in 31:05.54.
d) Last year, exactly 44 days after running 2:03:06 in Boston, Moses Mosop destroyed the WR of 30,000m on track in Eugene, running 1:26:47 (technically better than his 2:03 in Marathon), and 31 days after Boston was able to run on track (2400m, earth) 18 x 1000m with the first 2:45, 16 times 2:42 and the last in 2:36, with 1:20 recovery.
We can have a lot of other examples. One thing in common : after the marathon, instead relaxing, these athletes used the big aerobic base they built for developing the specific speed endurance requested for the shorter distances.