On the upper link you can read the system's description and the way to execute it. Briefly of course. I did not include all the lifestyle factors, nutritional strategies and other important stuff, but mostly the training options. It is very understandable. Please go through it before you hit this post !
The why and the how
As we know the MAF training intensity is in between heart rate ranges of (180 - your age) and (180 - your age - 10). For instance in case of a 35 year old athlete it is 145 to 135 !
There are so many cases where we can fall back to this very basic idea and get extreme benefits. The most obvious ones are recovery and base training. High milage training, interval sessions, speed building periods leave the body in a high fatigue state. You can include one or even multiple weeks or months of MAF with strategic MAF style speed sessions and recover very well, before you hit another set of track sessions.
For me personally the most benefits come from the saying of Phil, that the body remembers. The body doesn't forget speed, just like this. If basic stimulation is applied often enough, it needs 1 or 2 years to loose the total sense of speed and high end. I set my 1:15 half PR on 6months of exclusive MAF. MY HR never went over 150, ever for 6months during training.
In case of multiple races, or a longer period, like an entire summer of 2months worth of races and adventures, the MAF system is a killer.
It feels like that you are stretching out your taper/peaking for a length that is normally not possible. In reality it is not 100% fitness after a while, but damn close to it. For athletes with really high end fitness, it is more than enough. I am 100% sure that with a proper approach and knowledge it could be translatable to cross-country or indoor track season too, but I don't deny, that the entire MAF system is much more easier to apply to longer endurance activities. Half marathons to ultramarathons.
I recently for instance coached an athlete to get his speed back and to prepare him for the up and coming September season. It was 8months of quite intense and fatiguing training. He needed that long, structured, track infused major cycle, as in the last 3 years he focused on ultra-distance mountain races and while he kept his leg speed from the downhills, his resistance against fatigue is kind of diminished.
As an example, he can run a sub 1minute 400 on the track, but going for 14 x 400 @ 1:18/r45 did not happen. The same was true to longer intervals. A 3:05 on a 1km strava segment went out easily to him, but (5 x 1600 @ 3:40/km /r60) or a (5 x 1000 @ 3:21/r3min) was not possible. I mean at all ! His high end finishing speed remained as it was when training with a track club, but resistance and speed endurance was very much non-existent. Either ways, it all came back during winter. We cut volume and threw out all jogging around and easy workouts. No freckin' easy running. If he wanted to get in an easy workout, I sent him to the track and made him do a mobility set, then a focused athletic schooling drill session. 60minutes top. No jogging around and wasting time! His milage was down to 30 to 60km a week, while maintaining the same workout hours of his previous 120 to 150km weeks. This means, that yes, we really hit those specialty knee raises, sled drags, sprints, jumps, plyometrics and applied quite long recoveries. I sent him some basic parcour youtube videos to learn some basic moves of opening up his hips while working on core strength in the mean time.
Anyways from a 38min 10km shape, he is now running 38min 10km as part of his weekend long runs and he is closer to 34:30 as his workouts indicate !
What I want to say here is that we trained from September to April. This is when we go for the MAF, as the summer trail running race schedule is packed. It is packed because people love that here in France. Meeting up every second weekend. Building up distance and completing not only 5 to 15km races, but ultra distance events too. However, with the MAF tactic, it won't risk anything and actually on the contrary. It will be elevating and strengthening the runner.
There is also one thing to think about, especially for faster runners. That is speed. The more you run faster, the faster you become. We can approach this from different stand points. When using a regular 80/20 approach, we might often hit sub 3 minute paces and on tempo runs a lot of kilometers of that 20% might be done at sub 4minute pace. However 80% of that time when we run easy, sets our general speed quite low. The average speed of a 35minute 10km runner might be like 5:30/km for a week or for a month.
On the other hand if that runner was fit and would be doing exclusively MAF for a while, the average weekly / monthly speed might be on the 4:15 - 4:30/km range. This is a a whopping 1minute per kilometre difference !
While this subMAX performance training routine feels like a perfect lifelong practice for never-ending improvements, it is surely not. It is something to add as a cycle of micro or macro priority.
I do all mixes. I might train on subMAX 95% of a time, but in each 10day schedule I add 1 interval session and one tempo run.
I also might go for a classic 80/20 approach for 3months, than sit back and subMAX for 5weeks exclusively. I still do hill sprint and very fast low heart rate downhill intervals though.
Your objective is to be the most versatile. The least tired. The faster. You want to recover the quickest possible. I recommend for people with some geeky knowledge to look back at their training dairy. What is the average pace of your years, for what mileage, for what average heart rate, with what elevation gain. It can be extremely interesting to see.
The thing about MAF, that you can do more, faster, more often and better with. However the human body adapts and should be derailing from it time to time, to get stimulus what triggers new adaptations !