I think there are a couple of things to keep in mind about the Ingebrigsten's training. Firstly the more commonly circulated schedule of Double Threshold twice a week and the hill reps once a week is their base training. If you want to get super crazy aerobically fit then yeah getting a ton of volume at a high end/threshold effort is going to get you there. But there training changes a bunch when the racing starts. You'll see that it is said that all they do it replace the hill reps with 300s at mile pace and thats it. But it has been reported that this is no longer true.
Specifically in this podcast:
Inside Running Podcast-218: Kristian From Norway Returns
In this podcast Kristian states that the 6 minute reps are no faster than "marathon pace", the 400m reps during the winter/base are at 10k pace and they'll cut down to 5k pace within the workout later on in the season/year. The 1000m reps are at around half marathon pace during the winter/base although theyll cut down to 10k pace later in the season/year.
The training beginning in April starts to change, but this is the part that they keep very hush hush about still. Again, in the podcast its stated that one of the staple sessions that they do 5x1000m w/2 min rec starting at 10k pace and finishing at 3k pace. Then they take a break and do 10x300 at 1500 pace. The 10-15x300m sessions is a workout they still do but only when there is a race coming up or in between two races that a little but close together. The goal for that one is just rhythm apparently.
As far as the specifics of their training that's all I really know.
But as to the science behind why their base phase works.
You have to remember that there are so many factors that affect endurance performance and even lactate threshold velocity. But some of the big ones are mitochondrial density and function, lactate utilization, fat utilization, and lactate clearance.
The other big thing to remember is that there are multiple ways of targeting all of these physiological components. This is simply a way of doing that.
But lets dive into the specifics.
First is mitochondrial density and function, specifically in slow twitch fibers. I know tinman likes to talk about intermediate fibers a lot, but you need the slow twitch just as much if not more. There are three main ways you can target mitochondria in slow twitch fibers but they all revolve around the same goal. That is depleting slow twitch fibers of their energy stores. When this happens, the body starts making more mitochondria in those depleted fibers. So firstly, you have mileage/volume. No surprise there. You run a lot you deplete a lot. Secondly, you have long runs that preferably at a moderate intensity and over hills so you're recruiting different fibers. Thirdly, you have tempo efforts. These tempo efforts can be anywhere from 75% vVo2 max or about 2 mmol to 90% vVo2 max or just over the traditional but somewhat inaccurate AT4mmol mark aka. Critical Velocity pace. For a while it was thought that these tempo efforts needed to be continuous in nature, but in Portugal and Norway theyve shown that this is not the case. You can run these tempo efforts at various speeds that range anywhere from 10 minutes to even as short as 45 seconds at moderate relative intensities with short recoveries and still get the same effect. What was found is that this allows for the muscle tissues to be spared and primarily only stresses the energy spectrum. The Ingebrigstens, at the counsel/suggestion of Marius Bakken, have decided to focus on the mileage/volume and tempo components of mitochondrial adaption. This is because long runs take a lot out of you and are a lot of pounding on the body in a way that chases fatigue and can in grain bad motor habits as typically they are performed at speeds that make it hard to have good healthy mechanics for the entire duration so weaknesses and imbalances occur if used improperly or if the athlete is not strong enough.
They are essentially attacking adaption from multiple directions, which in my view is the key to long term success and improvement in a specific quality.
Now for fat utilization. Why fat utilization? Well this falls in line with and is simply one component of what is known as the antiglycolytic principle/training. Basically the goal of this type of training is to maximize the power/speed in which you can perform without producing lactic acid which is a byproduct of aerobic or anaerobic glycolysis, or the break down of glucose into pyruvate. By maximizing your bodies antiglycolytic abilities you can spare fuels stores in your body for longer events or stem off acidosis as there is simply less lactate being produced. Fat utilization is achieved through long runs, specifically over 90 minutes in duration and tempo efforts in the 75-80% of vVo2 range or the maximum stimulation/contractile rate of your slow twitch fibers. Training at the tempo end of this spectrum helps maximize the potential of your slow twitch muscle physiology. The 6 minute efforts which are the most common ingebrigsten workout falls under this umbrella
Thirdly we have lactate utilization. This is the process of using aerobic enzymes, specifically H-LDH which transform lactate molecules into pyruvate molecules that can be metabolized into energy. Remember lactic acid is a miracle byproduct that gives us two components. Lactate and a hydrogen ion. The hydrogen ion is the bad part "poisons" the muscle and interferes with muscle contraction by affecting the pH balance. Lactate is the good part, if your body knows how to burn it, it's literally free energy. Your body gets very good at utilizing lactate as a fuel by having higher concentrations of H-LDH. In your slow twitch fibers concentrations of H-LDH benefit greatly from workouts that produce a lactate amount of 3-5mmol. This what the 400/1000m reps that the Ingebrigstens fall into and its what the Portuguese based most of their endurance workouts around. Specifically 400m reps at 10k pace with a short recovery.
Lastly we've got our lactate clearance, also known as the lactate shuttle. This is simply the ability for the body to transport lactate primarily produced by our glycolytic fibers (remember aerobic or anaerobic glycolysis). To other muscle fibers that can then utilize that lactate, like we just talked about, and ship it back to fibers in need of energy. This is accomplished through two proteins called MCT-1 and MCT-4. MCT-4 is found in fast twitch fibers and is trained through long maximal efforts of around 1 minute with very short recovery. They are brutal sessions that aren't necessary for 99% of distance athletes I would say. MCT-1 on the other hand is found in slower fibers and in intermediate fibers. They are trained through...you guessed it! mileage/volume, long runs, and a new term...isocapnic buffering workouts. Isocapnic buffering workouts primarily fall in a zone that is typically 8-12 seconds faster than than LT pace. This zone is special as it marks the beginning of increased lactate concentration in the blood/fibers because we are past that lactate threshold but is slow enough that there isnt a subsequent drop in blood pH.
Intervals are usually around 8 minutes in length with a short recovery of about 2 minutes. You can run a little bit faster for reps of 3 minutes with recovery periods of 60-90 seconds (think faster end of Critical Velocity) or even faster like 5k pace with 1 minute reps or at a slower pace that is at or close to the Lactate Threshold Velocity with reps of 10-20 minutes for a workout totalling 35-40 minutes of faster work.
The Ingebrigstens workout down to these pace once the season rolls around.
Anyway that was a very long post but I hope that answers a lot of questions. Hit me up if you have questions.
