Portugal is a very small nation but in spite of that they have a pretty amazing history of great distance runners. Their greatest legend has to be Carlos Lopes, Olympic champ and world record holder, but his 2:07:12 marathon best is no longer even the national record also it should be remembered that for much of his career many would have argued he was not the best of his contemporaries in Portugal. I don't know that this particular workout was ever part of Lopes training but I do know I got it from some training schedules of Portuguese marathoners. I also know I have since seen it in some schedules of top Spanish and Brazilian athletes.
This workout can be done with a huge amount of variety but it is very simple at its heart all the same. The workout is broken into two distinct halves. The first half is run very quickly from marathon pace to right around 95% marathon pace, if you are a 5k runner you can go for 85% to 80% 5k pace. Then at half way you make a huge surge and push the second half as fast as you can.
Basically you are making one big killing drive to the finish. This workout works great from 2k to 10k in total distance. The amazing thing is that you will often run the second half faster than you can manage for a time trial for that distance with nothing before it. Don't ask me why. I don't understand it but I know I have run the 2nd half of a 2 mile like this in 4:18 and my fastest mile time trial in a workout is 4:17. The fastest 1k I have ever done in a workout was the 2nd half of a Portuguese surge and I have read about other runners having the same experience.
I think this workout is best from 3k to 6k. It is long enough that you really do get a great aerobic session but short enough that you are able to really let yourself go in the second half.
The only trick to this session is that it is a SURGE at half way. You want to accelerate quickly and then try to keep that surging/accelerating feeling going all the way to the end. It is key to maintain that feel. It will keep you loose and FAST. If you do that you got it right. You may not always run great in the second half but when you are hitting it don't limit yourself the idea of this session is to just go as fast as you can.
This isn't a session I do a lot but it serves two great purposes. One it is a great tempo workout during your specific phase. You touch on relaxed tempo running and then get to hammer at race pace or faster for a long way. A great way to simulate the closing mile of a 5k or last 3k of a 10k.
The other thing it is great for is to break your tempos out of a rut or get past a seeming plateau. When I was coming back from mono in early 2007 I wanted to get my fitness back to where it had been prior to sickness, the goal I set out for the first half of the year was to run a tempo 8k to 10k on the track at 3:00 per k. I started with some slower stuff and repeats but pretty soon I did a 3k in 9mins and started building up. Then I got stuck at 5k to 6k for a month or more. I just couldn't seem to extend past that. So I did a run where I ran 5k in 16:00 and shifted for 3k. I ran 8:54 for the last 3k and felt STRONG. Sure enough two weeks later when I again attempted my regular tempo at 3:00 per k I rolled by 5k and 6k easily and was able to run 8k in 23:56. There is a huge difference between the fitness it takes to run a tempo 5k in 15:00 and that it takes to run 8k in 24:00. I was floored. It is still one of the best tempos I have ever done.
Now I'm not promising breakthroughs like that every time you use this session. In that case it was the perfect session at the perfect time. There are other times I have done and and not seen much more impact than any other session gives. It is a tool for the tool box but if you are trying to learn to be a powerful finisher over the closing miles 5k to half marathons or if your tempos have been stuck in a rut this workout may just be the key to unlock your next breakthrough.