I integrate fast finishes and faster tempo running in long runs for all distances. For the marathon, marathon paced work is included in long runs at various points of the build toward the race.
Why:
To teach your body to burn lactate.
To teach your body to recruit more muscle fibers. In this example, our intermediate muscle fibers.
For the marathon, to gain a better understanding of fueling and hydration requirements.
Examples:
10km Training
20 to 25 minute pickup at the end of a long run
30 min pickup in the middle of a long run
6 to 10 times 1 minute to 2 minutes surges halfway through a long run every 5 minutes.
Half Marathon Training
20 to 25 minute pickup at the end of a long run
In the middle of a long run including 3 km at marathon effort, 2km at half marathon effort, and 2x 1km at close to 10km effort. Taking 3 minutes easy between all.
Marathon Training
20 to 30 minutes at marathon pace at the end of a long run
Every two to three weeks replacing a long run with a marathon pace run. The volume of these build throughout the preparation period. For those who have not been exposed to these before, I suggest something like this:
13 weeks out 6x10 at MP
11 weeks out 5x15 min at MP
9 weeks out 4x20 min at MP
7 weeks out 2x30 min + 10 min at MP
5 weeks out 2x40 min at MP
3 to 4 weeks out 80-90 min at MP
More advanced runners may work up to 25 to 30km at marathon pace as they near the last 4 to 8 weeks of the marathon build.