This long run is named after two time New York City marathon champion and 2:06:34/59:33 man Marilson Gomes dos Santos, who I stole it from.
Top notch marathon performance isn't just about being very fit there are some complexities involved in it. This means there are many places that have very good running traditions where the marathon success is not on the same level. It also means there are pockets that consistently produce great marathoners. Everyone knows about Kenya and Ethiopia. Obviously they are on top of all the distance world. Many people are aware of Japan, a nation who has a 10k national record that wouldn't crack the top 10 all time in the USA but they have produced well over a hundred sub 2:10 marathoners compared with 16 americans under the same mark. There are however other smaller groups that fly under the collective radar of most of even the astute american marathon fans. One of these groups are the Brazilians. Within Brazil because of conditions and terrain there are really no fast marathons so unless an athlete gets out into international competition they are not going to produce a time that will make people jump up and take notice. Still with a fair bit of consistency over the last 20 years some of those athletes have been breaking out. In 1998 Ronaldo Da Costa set a than world record of 2:06:05. Another example Vanderlei de Lima was very famously attacked en route to winning the bronze medal at the 2004 Olympic marathon. Less well known is that he also ran 2:08:31 and won the Tokyo and Hamburg marathons. Dos Santos is another in this line of Brazilian greats.
I have found training info on this group, as a person who doesn't speak spanish or portuguese, is difficult. Their training seems to come from the Portuguese system, which has produced its own string of shockingly effective marathoners. Also most of Brazils successful runners have come from one or two small groups. One of the small pieces of info I have found over the years is this gem of a long run that is a regular part of Dos Santos training plan.
This long run is definitely a good marathon workout that can be done early in the marathon phase but also in the specific phase. This is also a good workout for a half marathoner or even 10k racer who is looking to build the ability to really move late in race when their legs are heavy and tired.
For the Dos Santos long run you run 12 to 16 miles at a moderate effort. The high end of your training pace, roughly 80% of marathon pace or 75% of half marathon pace. Without a break you shift gears and run 3 miles at around marathon goal pace, this is obviously not easy to do particularly the first time you try it so if you aren't used to shifting gears like this you may end up running as much as 5% slower than marathon pace. Don't worry about it. After you do this type of long run a couple times you will find that you can shift gears without issue. It teaches that lesson very well.
After 3 miles at marathon pace you again have to up the pace now for 6x400m aiming for about 5k pace with a steady 100m jog rest. You can do this on the track but I honestly end up doing it on the road most of the time. I have wheeled off a 400m straight and 50m out and back on either end for the breaks. Now in my current hometown of North Andover I haven't found anything close to 400m of flat in a row. There are no real beastly hills here but also no flats just a lot of lightly rolling and not so lightly rolling hills. So there are some small variations in my 400m and it is faster in one direction than the other but not in a big way. I try to go directly from marathon pace into the first 400m but if you are hurting you can start with a 100m jog.
The great thing about the 100m jog is that if you keep it paced reasonably and don't shuffle it you end up averaging around marathon pace for the 2900m to 3k, depending on if you start with a 100 jog or not, that you cover including the rest during the 400's.
This workout teaches the ability to run fast when your legs are very tired. It builds great aerobic power and helps make you more efficient in terms of the fuel you burn at faster speeds. IE it helps your body learn to burn more fat in place of glycogen even when running fast.
Progressing the workout. Generally I start with only 12 or 13 miles at the moderate pace and as I do the workout more I increase the volume at that pace up to 16 or more miles. So if the first time you run 12 miles moderate 3 miles at mp and the 6x400 you end up with a total volume of about 17 miles. If you build up to 16 miles moderate you will have a total of about 21 miles. Also this session is a great bridge to some of the very difficult specific long runs that Canova prescribes for the marathon specific phase.
Adjusting the workout. Now you may be looking at this workout and thinking that volume it just too much or you are 5k to half marathon racer or a high school or college athlete who has a lower general volume. You still want to be able to run fast when your tired and your legs are heavy and this can still be a great workout for you. You could easily drop it to 3 to 10 miles of moderate running before getting to the faster paced running.
There you have it a great workout from one of the great marathon groups in the world.