Why the Easy Interval Method approach is better than a polarized approach for 'normal' runners

In this video: (https://www.youtube.com/watch?v=MALsI0mJ09I) Norwegian physiologist Dr Seiler talks about his research regarding the training of world-class endurance athletes. The title of his speech is: "How ‘normal people’ can train like the world’s best endurance athletes”.
I disagree: Normal runners can, but should not, train like the world’s best endurance athletes. Too much slower running reduces running economy for most runners (not mentioned in the research of dr Seiler) and is not the most effective way of training the aerobic abilities of all your aerobic muscle fibers (slow twitch and fast twitch).

Dr Seiler found that many top endurance athletes apply an 80-20% (easy-hard) division in their training, a so-called ‘polarized’ approach. Next, he states that ‘normal people’ should do the same. Dr Seiler explains the polarized training in the graphs below:

According to these graphs, I can only conclude that Dr Seiler’s advice is that runners should perform 80% of their endurance running in low intensity zone 1 (= ‘can chat all along the way’). He calls this the green zone and advises to skip the aerobic zones 2 and 3, and perform faster sessions in the yellow and red zone. This is polarized training.

I oppose polarized training, especially for ‘normal runners’. The 1st reason is that a lot of slow running in zone 1 causes loss of running economy. A 2nd reason is that most 'normal' runners got a 50/50 division regarding slow- and fast-twitch muscle fibers. These fast-twitch fibers are partly aerobic. In order to recruit these fast fibers, a runner needs to apply a higher intensity (high-end aerobic).

Apart from this, the division 80-20 is not how, for example, double marathon Olympic champion Eliud Kipchoge trains. Have a look here:
https://www.prorun.nl/training/wat-doet-zon-eliud-kipchoge-nu-als-training/. In week 25-31 Aug 2017, 79km was performed in the high-end aerobic zone and 15 km in red zone, of a total of around 210km: 94 of about 210km = 44%. 73km in green zone 3 of 210km total = 37%.
Indeed, Kipchoge performs some endurance training at a pace of 15km/h or slower, but he also goes up to a pace of 18.5km/h. And he has interval sessions like 18x1000m (at >2000m altitude!) at around marathon pace, which belong to the high-end aerobic zone. Also, several of his so-called easy sessions are probably not easy all the way: when running at paces of 18-18.5km/h on a normal training day (not tapered and at > 2000m altitude, hilly environment), Kipchoge is running in green zone 3 intensity (high end aerobic), not in easy zone 1 or moderate 2. I conclude: this is not 80-20% or polarized training.

Similarly, the training of famous coach Arthur Lydiard is often used as an example of building an aerobic base with long runs in zone-1 intensity, complemented with hard tempo sessions in yellow and red zones. However, this is incorrect: his so-called long, steady slow runs were often quite fast and performed in a hilly environment: 800m uphill followed by long down hills, so more an aerobic interval training in zone 3 intensity. Anecdote (in my book):

Why do I oppose a polarized approach?
I am of the opinion there is a caveat for many runners who are applying this 80-20 division. This caveat is the damage to their running economy caused by the slow 80%, which could be accompanied with loss of running economy (decrease of ‘elasticity’ and ‘bounce’). As a result, a runner may well increase their aerobic ability which, theoretically, might take off one minute from their 10km time. However, they may also lose their running economy which may make them two minutes slower. Thus, their actual performance could be worse.

Why is the running economy of world-class runners not killed off by all this slow running?
1) Carrying less weight than the average runner. For example, Eliud Kipchoge, weighs just 52kg. With a low weight it is easier to maintain a reactive running style, even when doing endurance runs.
2) Being born with a superior natural reactivity. World-class runners, especially African distance runners, often have shorter calf muscles and thus longer Achilles tendons: longer Achilles tendons give better running economy (free elastic energy). Research of Gary Hunter at the University of Alabama at Birmingham (in 2011) found a strong correlation between tendon length and running economy.
Hence, two reasons why African top runners can maintain a reactive running style. Even when they run slowly, they bounce every step. Unfortunately, an average runner does not have the advantage of the longer Achilles tendon but does have the disadvantage of carrying 10-20 kilo more which may be a reason for not being able to apply a similar economic, ‘bouncing’ running style as the top East-African runners do.
3) Apart from that: world-class runners train so much (including strides), that all their slow running is compensated by enough fast mileage (remember: Kipchoge runs 73km a week at 18km/h or faster). Furthermore, East-African runners often train in very hilly environment which may cause a higher intensity running uphill, hence also training their aerobic fast twitch fibers.

Caveat of polarized training
Another caveat of polarized training is this: if you train your anaerobic system too much (20% in the yellow and red zone is what many runners apply… and that is too much in my view), then your anaerobic system will be come dominant too soon when running at higher paces. https://www.sisuracing.co.uk/post/what-is-vlamax-how-to-fine-tune-it-and-what-does-it-mean-for-your-anaerobic-capacity
“If your lactate production rate is high at max conditions (sprints), it is also relatively high at sub-max conditions (endurance events). Vice versa, if your maximum lactate production is low at max conditions, it’s also relatively low at sub-max conditions." I have experienced this myself and got similar feedback from other runners. Too much anaerobic training decreases the aerobic system: too soon your anaerobic system is dominant.

Train your extra aerobic engine!
Average distance runners have around 50% fast twitch fibers (which are partly aerobic), while most top distance runners have around an 80/20% or even 90/10% division slow twitch/fast twitch. On the website mentioned above: "By training at intensities just below the lactate threshold, it is possible to recruit the body’s aerobic fast twitch fibers, making them more aerobically capable and thus reducing the lactate production during exercise at low to middle intensities." So, if the ‘normal runner’ has 50% fast twitch fibers, why should they not exploit these fibers and add an extra aerobic engine? How to do this, how to train the aerobic skills of your fast twitch fibers?

Fast but relaxed, short efforts in the high-end aerobic zone will do the job! These efforts are skipped in a polarized training approached, but are a main building block in the Easy Interval Method, which is a total approach that does not first focus mainly on aerobic development alone but also on specific muscle strength and running economy at the same time, from day 1. Many runners who followed my advice reported that their aerobic endurance (+ running economy + times + enjoyment, amongst other things) improved after switching to training according the Easy Interval Method.

That '50/50' slow-twitch/fast-twitch runners should not do the same as '90/10' or '80/20' runners has also been proven by Belgian exercise physiologist Eline Lievens. In 2021 she found that most 'normal' endurance athletes with a 50/50 split in terms of slow- and fast-twitch muscle fibers require longer recovery time than the '90/10' or ' 80/20' athletes. I asked her if this also had consequences for the training. She gave the answer I expected: “The ’50/50 runner’ needs more sessions at a relatively higher speed in order to recruit the aerobic fast-twitch fibers, as too much slower training (easy) may not cause sufficient aerobic adaptations”.

No red efforts for slower runners
For slower runners (racing 10km and over) training in the red zone should be skipped almost entirely. Eg, for a 10km runner capable of running 50-60 minutes, training in the red zone (probably equal to 1500m intensity, which is far above LT intensity) is not very effective (and even counter-productive, as explained above), because in their 10km race they will run slower than their LT intensity.

So, do not train like the world’s best endurance athletes, do not apply polarized training, do not skip the high-end aerobic range of intensity. The reason this area is skipped in polarized training is that “it is too slow to achieve a major training effect, but too fast to get through unscathed.” Unfortunately, this is wrong: when training in the high-end aerobic zone (green zone 3) in a careful, smart way, you can very effectively train the aerobic fast twitch fibers and maintain, and even improve, your running economy, because the pace will be close to race pace. The Easy Interval Method shows you how to do this.

Download a preview of my book Easy Interval Method at dropbox and read enthusiastic reviews of ‘normal’ and top runners who applied the Easy Interval Method.
Or go to Amazon (for hard cover or eBook) or Apple (only for eBook).
(Dutch runners can buy the Dutch edition at:
Nederlandse hardlopers kunnen de NLse editie kopen via:
www.duurloopmisverstand.nl)

Some reviews here:

"The best kept secret in running!

This book is certainly the best kept secret in running. It capitalizes on the biomechanical and neurological deficiencies of the physiology focused approaches like Daniels, Mcmillan, Canova, etc. The easy interval method is truly a gem. Forget the Vaporflys. This is the best thing any runner could buy. For real!"

“Another aspect that I like about EIM is that it is not just focused on aerobic/anaerobic metabolic conditioning but is looking at the effect the training has on the nervous system and the muscle-skeleton system. Lok talks about "reactivity" or "bounce" you get from more exposure to faster paced running. This increase in what exercise physiologists call leg spring stiffness helps with running economy.

“I highly recommend getting this book. This method is especially useful to those that want an alternative to high-volume training or want to gain the benefits of interval training in a gentler way. I think masters runners, in particular, would benefit well from this kind of programming."

"Truly differentiated training philosophy"

"Very interesting book that proposes a training philosophy that is truly different from most other methods without going against the fundamentals of exercise science. The book is straight to the point and the main concepts are laid out very clearly and seem very logical. It would be interesting if the author could collaborate with researchers to further validate his method and contrast it against more traditional methods such as Stephen Seiler's 80/20 or Jack Daniels', especially for sub-elite runners."

"I’ve been using the EIM for over a year now, and it has rejuvenated my running with the benefits that many others have stated, including better economy, strength, reactivity and being injury free".