Interesting article, thanks 
I believe Seiler stresses that each rider should feel rested and ready to go before training. I personally canât recall him mentioning dehydration or fasted training in any video Iâve watched.
Hereâs the paragraph I was refering to. Could be I misunderstand it:-
Quote
"Level One
All overdistance workouts will be done at level one. Although the effort may seem ridiculously easy at first, it is essential to maintain close control and complete this training within the zone. In the end, the effort, because it is longer than other types of training, will be quite fatiguing due to energy and fluid depletion. r or these reasons, overdistance workouts lasting over 75 minutes should be considered moderate- to high-stress sessions, despite the low intensity. Most strength workouts will elicit heart rates at this level as well, depending on the exercises and the tempo at which the athlete performs them."
Unquote
Not at all. There is a video on this specific graph where he stresses several times that you should stay hydrated and fueled when doing this kind of ride where yo check for decoupling. Will look it up and post a link later.
The video link is in Intervals right below the decoupling graph.
Not only here. In a Youtube video from a couple months ago, he specifically apologizes for creating this confusion. Thatâs the video where he ârewordedâ HIT/LIT sessions into a bucket with easy and a bucket with hard workouts.
Another widely spread confusion is the 80/20 distribution based on TIZ. Thatâs not correct! The 80/20 principle is based on number of sessions.
Absolutely. Once you have some experience, you clearly feel the difference in a more central fatigue occurring after a long low intensity ride and the more peripheral fatigue of a hard interval session.
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I must admit I think my original question has not been correctly understood by some. Could be my grammar being at fault. Basically âis 90 mins Z1 a High or low Intensityâ
Secondly, I believe the 80/20 distribution, which incidentally Seiler doesnât seem to be very keen on using is âtime/durationâ not numbers of sessions. That is to say, if you train eg. 10 hours a week then 8 hours +/- should be low intensity. But here again, Seiler is not rigid and seems to err on more low than high, until nearing race season that is when he suggests tweaking the sessions in preparation for racing.
I do agree that over time experience will determine whether one is working low or high. After 3 months Iâm still feeling my way and do find 90 mins more fatiguing than I would have expected.
I perhaps should also mention that the 3 zone model I am using does divide zone 1 into two secondary zones as is zone 3. See attached
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90-mins in Z1 is low intensity irrespective of duration. Z3 would be high intensity.
If it âfeelsâ hard, then it probably is hard; thatâs RPE, itâs subjective thing.
If it is hard, then there could be underlying condition(s) making it hard, eg. Incorrectly set threshold, low level of fitness, illness, co-morbidity, etc.
You should be able to ride in Z1 for much more than 90 minutes before it gets too hard. A beginner might struggle at first because of the duration, but the more you do this, the more you get better at it.
Efficiency Factor and Decoupling are used to measure the progressive change in performance.
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Yes. Thatâs the paragraph I recall. In more recent terms I believe he is saying that LSD workouts are low intensity but high load, i.e. fatiguing. That is the way I interpreted it when I read it years ago and corresponds to my experience.
A definition of intense :- extreme degree of strength, force, energy, or feeling.
As commented previously by GeraldâŚZ1 work is not intense; Z3, in comparison, is.
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Z1 is not intense, but can become âhardâ if you do it long enough.
90min Z1 for someone who hasnât been moving for months/years can be âhardâ. But I agree that it isnât âintenseâ 
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If you havenât been moving in years, you wonât be able to stay in heart rate Z1/3 for long. Two years ago I would hit Z3/3 just riding to the end of the block.
Well, you got that wrong. But I can understand why. The correct information got burried in a lot of incorrect interpretationsâŚ
It originates from a question asked by an interviewer to Seiler:
"What would Polarized training, 80/20, look like if you put it in a TIZ tabel? was the question.
Seilerâs response: âOoh, it will look more like 90/10 or even a bit higherâ
And he meant: if you do Polarized correctly, the TIZ will not look like 80/20 but more like 90/10. He never said that 90/10 was the way to go to design a Polarized plan.
And people started to interpret that as if Polarized should be a TIZ distribution of 90/10. But it is perfectly possible to make a plan with 90/10 distribution that has nothing to do with Polarized.
Seiler realized this not so long ago and made a video where he explains again the basic principles of Polarized, with a better terminology and making it even more simple.
80/20 distribution based on number off sessions
2 workout categories (and no longer 3): Easy and Hard
Easy is below AeT, Hard is above AeT (he no longer advocates Z2 should be avoided)
And any session can become a hard one if the duration gets long. Thatâs the part that you have to judge by RPE.
The Hard workouts vary from Coggan power zone 3 to 6 and you choose them depending on the kind of events youâre training for and the training block youâre in.
People training for long events will focus more Tempo and Threshold, while crit riders will focus more on VO2max and Anaerobic.
While in a Base block, you will rather do Tempo, Sweetspot iso VO2max. But in a Peak block, you will choose the higher intensities.
Thatâs a totally different story compared to doing 90% of your time below AeT and the other 10% at Vo2max or higher intensity.
Video has been posted before:
And now I just have to wait until someone starts flaming me 
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I should have added more context to my reply. I have definitely noticed the HR/PWR decoupling in my easy rides but there are so many things that can cause it, including dehydration, insufficient fueling, excessive heat, or even a brief effort outside of Z1. Upon reflection, I would interpret Seilerâs advice the same as the classic advice for intervals, namely: you should stop the intervals when you stop recovering in the interval rest period. So for Z1 you are trying to ride as long as possible before the decoupling occurs. Once the decoupling occurs, you are no longer benefiting from a Z1 ride even if your HR goes back to Z1. So the best Z1 training would be fully hydrated, fueled, cooled, etc so you can ride in coupled Z1 as long as possible.
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True, I should have added Z1 Power but Iâm getting so used to power zones that I forget to specify.
Hmm⌠I can definitely make much more than Z1 power in Z1 HR before the decoupling occurs, and I can also ride in Z1 power after the decoupling occurs. So I would think Z1 is more about HR than power, although you need the power to identify the decoupling.
Iâm still not entirely following you.
Riding Z1 doesnât mean that you have to ride bang on your AeT, it means riding about 5-10 beats below AeT. That gives you some room to decouple and still stay in Z1. You should ride long enough to inflict some decoupling because thatâs what progressive overload and adaptation is about.
Damned, these zone definitions definitely make it hard to explain. As you say, there are two ways to determine decoupling. Keep power constant and let HR drift up or keep HR constant and let Power drift down. But most people talking about decoupling base there discussion on a HR drift caused by constant Power.
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To add to this section, Seiler says that Z2 can be done, but it would typically be for a longer duration than a Z3 workout. It also tends to be an the extremes of this zone, so some upper end Z2 and Z3 would be considered a hard workout.
The same happened with Sweet Spot; it also got taken out of context, and Frank Overton had to go back to basics to explain what it was intended to be. But thatâs another topic for another thread.
My main point is: striving for the decoupling cannot be the goal of Z1 training because it is trivial to force the decoupling whenever you want. So it seems to me the goal must be to stay in the coupled state as long as possible.