The total approach of the Easy Interval Method, aimed at running economy, aerobic endurance and the right 'fuel supply' in almost every session

Easy Interval Method: lighter, well-balanced, effective… and more enjoyable!
The well-known physiologist, Stephen Seiler, observed top athletes and their training methods.  He found that they had an overall intensity distribution of a roughly 80/20 ratio (easy/hard or low aerobic/anaerobic) in their training and concluded that the 'normal' runner should also train in this way, i.e. the same intensity distribution. This is known as the polarised model. In a Youtube video he says: "Normal athletes should train like the world's best athletes". I don't agree: about half a century of experience with top runners and 'normal' runners, has led me to the conclusion that the 'normal' runners in particular should not train like the top runners: for them the 80/20 approach is not the best way to train the aerobic function of the fast muscle fibers and running economy.

(Please be aware that in this article, I use aerobic zones 1, 2 and 3: zone 1 (easy), zone 2 (moderate), zone 3 (fast). Next, zone 4 is around the anaerobic threshold and zone 5 is anaerobic. Seiler uses a different zone-distribution.)

The reason that the polarised model mainly advises training in the low aerobic zone (zone 1) and skips higher aerobic intensity (especially the high aerobic zone 3) is that "training in that high aerobic zone would be too slow to achieve a large training effect, but too fast to get through it unscathed." The first is very incorrect, the second is true if you train regularly (often 2 times a week) in this zone in the form of fast endurance runs: then the vulnerable fast muscle fibers will get exhausted. However, the Easy Interval Method shows that if you train in this aerobic zone 3 in a careful, smart way, you can achieve a "great training effect" and can also "get through it unscathed".

I will explain why this popular 80/20 training is not the most efficient training for the 'normal' runner and easy interval training is.

What is basic training?
Slow endurance training in zone 1 is widely regarded as basic training, aimed at developing the aerobic system. When performing these slow runs, a runner will predominantly train their slow-twitch muscle fibers. I believe that is an incorrect starting point, or perhaps I should say an incomplete starting point, for two reasons.
1) Basic training should also be aimed at making the most of the so-called ‘reactivity’, the resilience (‘pop’, bounce’ in your legs) of all leg muscles, but especially those of the tendons and muscles of the feet and calves. Unfortunately, this is a neglected child for most normal runners. The vast majority of normal runners develop a 'heavy' running style with far from optimal 'reactivity', and running economy, due to slow endurance runs.
2) Basic training should not only focus on the aerobic function of the slow twitch muscle fibers (with the emphasis on fat burning), but also on the aerobic function of the fast-twitch muscle fibers (where the emphasis is on carbohydrates as fuel and the use of lactate also plays an important role – see Dr San-Millan's graph below).

The starting point of the Easy Interval Method, beautifully expressed by the American coach Nate Jenkins, is different:
"From the beginning of our running, we should be doing daily work to build our muscular skeletal system to excel at the specific demands of running and running fast. How? Mostly with fast, relaxed running."

A runner who includes the above aspects 1) and 2) in his training will significantly improve two neglected 'engines' and experience has shown that this gave runners who hadn’t progressed for years, a large improvement over various race distances.

Dutchman Berthold Berger said: "My 'reactivity' increased to a level I had never had before". From a mediocre runner, he became a national athlete in three years times, winning medals in Dutch championships.
German runner Andres Keil said: "I feel like an aerobic monster".  After 10 years of stagnation, he improved his PB’s at the age of 35.

Why does the 80/20 approach work well with top runners, but does the Easy Interval Method work better for the ‘normal’ runner in particular? Main reasons: difference in body weight, talent, training volume and composition of muscle fibers. I will explain this below.

1. Body weight, talent and training volume - top runners maintain their running economy
Top runners are almost all lightly built, have thin legs with resilient muscles and tendons and perform up to 12 (or more occasionally) running sessions per week, in which many fast kilometers compensate for any lost resilience and running economy.

2. Top runners have a favorable distribution of slow versus fast muscle fibers.
It is well known that muscle fibers can be divided into two different main types: slow-twitch (type 1) and fast-twitch (type 2). On average, most regular runners have about a 50-50% ratio of type 1 to type 2 fibers in the largest leg muscles. However, top long-distance runners have a much higher percentage (about 80 to sometimes 90%) of slow-twitch fibers, while for top sprinters it is the other way around.

Slow-twitch muscle fibers (type 1) are mainly used in relatively slow endurance activities where the aerobic energy supply is dominant. They can - after the necessary training - sustain such an effort for several hours. Fast-twitch muscle fibers (type 2) are mainly used in activities with a higher speed and a higher use of anaerobic energy. The downside is that type 2 fibers tire faster.

It is also generally accepted that type 2 fibers possess not only anaerobic, but also aerobic properties. These aerobic properties are mainly used at higher speeds, not only at 800 and 1500 meters, but also at 10 kilometers, and even at the marathon. During a competitive effort, a mix of all types of fibers is always used.

Despite the fact that the aerobic properties of the muscle fibers type 2 play a serious role, this fact is not correctly translated by many runners into the composition of the training that focuses on aerobic fitness, and by that, I mean a broad aerobic condition. The general consensus is that many slow, long runs need to be completed to improve aerobic endurance – this means mainly training muscle fiber type 1. Even many 800 and 1500m runners complete slow endurance runs, because they see this aerobic training as the basis for their race distance. This has led to a (in my view inefficient) training vision that has persisted for many decades: the main share of aerobic basic training by runners from 800 meters to marathon is performed in zones 1 and 2, with the largest share for zone 1. In terms of fuel, fat burning plays a leading role in slow endurance runs, however, in races, especially 800 to 5000m, mainly carbohydrates and lactate are being used as fuel.

Scientific research: 'normal' runner needs more recovery time
Heavier efforts in aerobic zone 3 are also considered useful, which is why some runners regularly complete fast endurance runs at this intensity. Unfortunately, despite the fact that these zone-3 efforts are mainly aerobic, experience has shown that for most runners, two or more of these fast endurance runs per week are too taxing. This is especially true for runners with a 50-50 split in terms of muscle fiber typing.

It is mainly the type 2 fibers that become fatigued as a result of such a training load. As a result, several of these workouts per week do not lead to the intended improvement in aerobic endurance and can even cause overtraining. In this context, scientific research carried out by the Belgian exercise physiologist Eline Lievens is very interesting. She found that endurance athletes with a distribution of about 50-50% between slow and fast muscle fibers need more recovery time than top athletes who often have a distribution of 80-20% (or even 90-10%).

Different muscle fiber type, different training accents
I found that interesting and asked her if this could also have consequences for the training. She gave the answer I expected: "A runner with more type 2 fibers needs more sessions at a relatively higher speed (zone 2 & 3 – moderate & fast) in order to recruit the aerobic fast-twitch fibres, as too much slower training (zone 1 - easy) may not cause sufficient aerobic adaptations. This contrasts with the currently popular 80/20 intensity distribution.

The above explains why the Easy Interval Method works better for most normal runners than training programs that use endurance running training as basic training: gratitude to better training of the aerobic function of the fast muscle fibers type 2 with more mileage in the aerobic zone 3, that runner will develop a much better aerobic function of his type 2 fibers.

However, to prevent this 'vulnerable' type 2 from becoming overtrained, it is advisable to train it mainly in a light way and with sufficient (almost complete) recovery. The Easy Interval Method does this in a safe, efficient and enjoyable manner.

The American physiologist Dr. San-Millan also showed the importance of training zone 3 (and zone 2). He did this from the perspective of 'fuel supply'.


Fast muscle fibers want fast fuel: carbohydrates
With slow endurance training in zone 1 and low in zone 2, a runner will predominantly train their slow-twitch muscle fibers and the fat burning system (see graph above). However, because most runners have a distribution between slow- and fast-twitch muscle fibers that is on average around 50-50%, it is illogical to focus the main share (~80%) of the training unilaterally on the slow-twitch muscle fibers. As mentioned earlier: at higher speeds, in races starting at 800 meters, a large proportion of aerobic fast-twitch muscle cells are also used, for many runners even in the marathon. These cells are not naturally set up to burn fat, but are carbohydrate specialists. They use glucose (carbohydrates are converted into glucose) as their main fuel, partly forming lactate (lactic acid). That lactate can be used again as extra fuel. This has consequences for training, as shown in San-Millan's graph: high in zone 2, low in zone 3 you have a mix of fat and carbohydrate burning, as well as utilization of lactate, while high in zone 3 and around the anaerobic threshold, lactate provides an even greater share. Easy-interval training provides a good mix of usage of these three types of fuel.

Is training in zone 1 completely useless? Not that either: in zone 1 we train the production of mitochondria (oxygen factories), but that also happens in zone 2. In zone 2 we also make capillaries (necessary for transport of blood), so that zone 2 seems to be more important than zone 1. Incidentally, zone 1 is also regularly trained in the Easy Interval Method: gratitude to the warm-up & cool-down, and the long recovery breaks, you will make several 'hidden' easy mileage in that zone (for example, when performing 4 or 6x1k, the total of fast (high-end aerobic) kilometres is 4 or 6, the total of easy kilometres about 7 or 9).

Lactate shuttle: ensure proper intensity and long recovery

And when it comes to using lactate as fuel, many runners at distances up to 10 kilometres apply an incorrect method. Lactate shuttle is the key word here. The essence of the lactate shuttle is this: producing lactate with an anaerobic effort and then using it aerobically as fuel. What is the best training for this: a heavy anaerobic effort or a light one? Search on the internet, and you will usually find that a heavy anaerobic effort is chosen: a fast 1k to 2k at around 5km race pace.  (Actually, 'pace' is already an incorrect choice, because you should aim for an intensity, which - at the same pace - will often be different when racing compared to training – I discuss this in my book). After the fast 1k or 2k tempo, 2-3 minutes of active recovery is prescribed, next repeat this another 3 times. This is heavy and you can't do it more than once a week.

Moreover, it is a contradictory approach: when performing such a heavy anaerobic session, a considerable lactate accumulation will take place, causing the anaerobic system to dominate significantly, while the goal should be aerobic recovery, using lactate aerobically as fuel.

Relatively low lactate values and long recovery breaks = no lactate accumulation, more minutes for aerobic usage of lactate
However, aerobic recovery (in which lactate returns more or less to starting level after each rep) during a lactate-shuttle session, can only take place if the production of lactate remains limited (lower than lactate-threshold values), combined with long recovery (up to 5-6 minutes when performing 6x1k). This combination ensures that lactate accumulation will not take place and that you train the aerobically burning of lactate for many minutes more compared to a ‘traditional’ session, in which you run at race pace with just 2-3 minutes recovery.

After such a relatively light EIM workout, a reasonably trained runner will be recovered the next day, which allows them to perform a lactate shuttle session in every workout, not just once a week. This has similarities with the Norwegian method (Jacob Ingebrigtsen!), in which this is done up to four times a week. However, the recovery breaks in the Norwegian approach are shorter and not everyone can handle that: an EIM runner switched to the Norwegian approach... and performed worse.

Thanks to the frequent training of the aerobic 'carbohydrate/lactate engine' with easy interval training, you will get better at burning lactate and subsequently acidify less and later at higher speeds.

An additional advantage: the 'normal' runner who trains according to the Easy Interval Method is usually trained so well in zone 3 (and reasonably fast runners also in zone 4) that for race distances longer than around 30 minutes, they do not need to do any anaerobic training in zone 5. And shorter-distance runners need very little hard training in zone 5.

I hadn't trained any heavy anaerobic paces for six months and ran a 10,000 meters in 28:24 (I only performed a few fast endurance runs of 7-8km and four cross-country races). When I didn’t need it for 28:24, why should a slower, ‘normal’ runner perform 20% of his training as hard anaerobic training?

The following makes it clear in another way why the 80/20 approach is far from optimal for a slower runner
The polarised 80/20 model is based on schedules of fast runners, but the usefulness of 20% training at paces around and above the anaerobic threshold - zone 4 & 5 - is very debatable for most normal runners. (Seiler recommended 4 x 8 minutes with HR = 90% of HRmax and 4 x 4 minutes with HR = 93% of HRmax; described by an ordinary runner as extremely heavy - Seiler later reconsidered this).  

Why would a slow runner, who completes the 10 kilometres in 50-60 minutes or slower, which for many runners is slower than the anaerobic threshold, spend 20% of their training at an intensity around and above the anaerobic threshold? An intensity that will probably only be reached in the final sprint, for 1-2 minutes...

For a slower runner training stimuli high in the aerobic zone suffices when training according to the EIM. In this high-end aerobic zone, the anaerobic system - utilization of lactate - is also trained, because we always use all energy systems. Intensity distribution should be adjusted individually, as well as per race distance, which leads to the conclusion that this intensity distribution of 80/20 is not generally applicable anyway.

But what about Lydiard?
You may now be wondering: what about the long, slow endurance training promoted by the legendary coach Arthur Lydiard? There are many misconceptions about Lydiard's training. He only propagated slow endurance runs as recovery (which I also oppose; I describe better recovery methods in my book.) This misinterpretation of the Lydiard Method started a long time ago, as the following anecdote Illustrates:

Physiologist Dr. Hans Keizer, former national coach and team doctor of the Dutch Athletics Union, once told me how easily the 'Lydiard approach' can be misinterpreted. In the winter of 1968-1969, Arthur Lydiard gave a lecture in the Netherlands in which he spoke about his

long runs for middle-distance runners. Several Dutch top runners followed suit, including Keizer's wife Ilja Keizer-Laman (6th in the Olympic 1500m in 1972 – best time 4:05). Unfortunately, all runners performed worse in the summer of 1969. It was only in the autumn that some managed to match their performances of the previous year (gratitude to regular races and fewer endurance runs). Dr. Hans Keizer: "Only later did we learn that Lydiard's endurance runs were actually high-end aerobic interval training, with 800 meters uphill and recovery during the descent. In the flat Netherlands, however, it became a monotonous, slow endurance run for us with which you 'untrain' the fast-twitch muscle fibres."

Multiple training effects in one session; the total approach of the Easy Interval Method!
In conclusion: the Easy Interval Method is characterized by a total approach that, from the beginning, addresses the endurance of the aerobic slow and fast-twitch muscle fibres, as well as specific muscle strength and running economy. And uniquely, all these training effects are addressed in almost every session.

It is true that with more training in zone 1, top runners (with 10-12 sessions per week) will run faster. However, the 'normal' runner (with 4-6 sessions per week) who spends separate training sessions at zone 1, then lacks time to implement sufficient training sessions aimed at the high-end aerobic zone and aimed at running economy. An EIM session, for example a session aimed at zone 3 (with ample recovery between the reps), is much more effective for this runner because in such a session, zones 1 and 2 are automatically included (intensity goes up and down from zone 1 to zone 2 and 3 and back), making separate zone-1 training sessions unnecessary.

More and more runners are experiencing that such a total approach is better than a model in which so-called base training mainly consists of easy endurance training.

Unlike Dr Seiler, I say: "Normal runners should not train like the world's best runners"!

In the book 'Easy Interval Method' you will find schedules for all distances from 800m to marathon, from training twice to 7-8 times a week. A preview of the book can be downloaded for free via www.easyintervalmethod.com. In this preview you can read the experiences of other runners (top and ‘normal’ runners) from all over the world and it describes what all you can expect in the book.

Finally, the opinion of two American runners, posted on Amazon.com:

Ken S, USA: "As an over 65-year-old experienced runner, Easy Interval Method (EIM) is a preferred training method over the frequented stress and injury-related traditional methods of training. EIM benefits: less stress on my joints, improved recovery, performance, health, enjoyment from running. I highly recommend it.

Brian Bryant, USA: ‘Game Changer’
Reviewed in the United States on May 28, 2024
“After 3 years of running at low HR I discovered some new ideas about 6 months ago, and my race times, training enjoyment, recovery times, and run-life balance have all improved. I have read at least a dozen well known books. This book explains things better and is easier to understand than any so far. I am 60 yrs, 175 lbs, and am now running some of the best training and racing of my life.
Some books, like The Nine Mile Marathon, Run Less Run Faster, and Run By Heartrate (which directly references this book), are all good and really helped me switch away from the long slow miles, high mileage weeks, long runs, and cumulative fatigue that so many books, videos, and training plans promote.
Then I discovered this book (Easy Interval Method). The author really digs in and gets to the heart of the Why, with detailed explanations of the physiology, which are easier to understand than The Big Book of Endurance Training and Racing, 80/20Running, and several others I have read.
This book also gives some excellent starting points for the Whats and Hows that are easy to understand and adopt.
Having spent hundreds of hours reading books, blogs, articles, and watching countless YouTube videos, I will say that this book is what I have been looking for and I cannot recommend it more highly. It is a hidden gem.”