Most of you probably never heard of Jan Helgerud. But in Norway he has made quite some commotion, his method was applied by svein tore samdal who trained marrit bjoergen using this method. Kalla also started using this method and has also performed quite well at skiing.
The theory states that vo2max training best stimulates aerobic development. He used a more scientific recent model to prove that stroke volume doesn't level of after 65% of maximal heart rate. and in his eyes increased stroke volume = improvement in vo2max.
To this point it is not really applied in many sports but cross country skiing though it is done enough in athletics if you see what is meant by vo2max training for jan helgerud.
He is happy when you train at or over 90% of maximal heart rate. His traditional sessions also only keep your heart rate there for about 6 - 10 minutes. Other coaches are even a bit less strict and seem to be happy starting at 85% of maximal heart rate for training as the curve already moves up then.
APPLYING ON ATHLETICS
So basically when you read what frank horwill wrote down in his articles you get training like jan helgerud likes to see it. Except then Helgerud is big on one thing.
He likes to see athletes do crash training. But he doesn't talk about upping volume, actually training volume should drop completely in favor of intensity.
In such blocks he recommands athletes to work twice a day at 10 km intensity for 20 minutes worth of intervals (4 x 5 minutes or something like that).
On the non 'block' weeks an athlete focusses on remaining the improvements (your heart rate should have dropped in the block for your 10 km pace thus you need to up the pace a bit and do reps at the new pace (lifting heart rate between 90% - 95% of mhr).
At this point we talk of 'maintainance' and focus should be basic endurance. You do 2 - 4 'vo2max sessions' (2 should suffice for most athletes).
Other sessions then are mostly long runs and recovery runs.
One of the long runs supposed to contain a lot of intensity at 2 mmol.
So a 'non block week' could have 3 - 4 stress sessions.
Second thing Helgerud is big on is strength, he likes athletes to do strength training focusing on maximal intensity and low reps. Most important for runners are (His vision) half squats. These should be done at least twice a week.
We could extend the paces to 3000 meter - 15 km pace and still fall in 90% - 95% of maximal heart rate in the first situation reps are just 3 minutes and in the lather about 8 minutes each.
But hearing from one of the co-workers paces could be token further down. To a 30" - 30" session at 1500 meter pace as this creates 'almost' equal adjustments in the heart per session.
MOST PROFESSIONAL RUNNERS PROBABLY DO SO BUT NOT NECESSARY ALL
Most of us do threshold runs where heart rate will raise to 90% of maximal heart rate for more then a few minutes. I guess runners like ryan hall and ritz (when in marathon training) are doing maybe up to 20 minutes per tempo session at such percentage of maximal heart rate. When running 4'30" - 4'40" miles.
Others use 5 km reps or 1500 meter reps in training with little recovery.
The biggest difference probably is that most runners use little to no blocks of 10 days.
THEORY IN PRACTICE
One of the co-workers ran a 2 hour 40 marathon on similar training (30" on and 30" off) three days a week. It would not be note worthy unless you say he is 45 years old and had a vo2max of 75.
One skier (pro) raised his vo2max from 73 to 80 after just 2 - 3 weeks, his heart rate at all paces also had dropped after this experiment.
NECESSARY FOR GOOD PERFORMANCE
I don't know, i just thought to write it down here. I have heard story's of 15' 5 km runners only doing runs at 9 - 10 minutes per mile doing no speed work what so ever, never touching the 90% + maximal heart rate.
Hard to say, some people will say it is more troubling to the immune system then just pledging along at 65% mhr. True but you have recovery in between and most likely the immune system could adjust to the demands placed on it. It is not that a recreational athlete is going to do long blocks of this stuff nor is going to do this a lot.
If you look at the pace it also is not a hard workout on it's own.
I guess most people will agree that 4 x 5 minutes at 8 - 10 km pace for them is not a killer workout.