I think a lot depends on how close LT1 is to LT2 and their relationship to Vo2max. The closer they are together, the greater the aerobic load at higher training intensities. Consequently, a 60min Z2 workout for a pro is much more difficult than for a mere mortal.
Z1 training in a 3 zone model is all under LT1. Low Z1 is restorative, recovery work, while upper Z1 would be ‘base’ aerobic training. Duration is relative to your own fitness level. 60, 90, 120mins can all ellicit similar adaptations for different athletes. Getting a feel for when fatigue starts to creep in to your legs is a good marker of when you’ve done enough.
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Yes, I was having similar thoughts. My last 10 mins yesterday at the higher end of my Z1 felt relatively hard. But, does that make the entire ride a HIT ride?
The important thing to judge is how much time you need to recover from the workout, be it a LIT/HIT/Easy/Hard… Because, ideally, you should not train again before being sufficiently recovered. So until the day we have a device that accurately can measure our recovery state, we will need to base our judgement on what we have now. Our subjective feeling, RPE, HRV, recent load, sleep duration/quality…
Training in a fatigued state draws us in a negative spiral, resting beyond the point of 95-100% recovery makes us loose built-up fitness.
The whole quest of science based training and all the different models is a search for the most efficient training plan that makes us gain fitness as fast as possible without having negative side-effects. Doing the right intensity, duration at the right time.
Better and better tools are developed to help us judge, but we are still in the “guestimate” state. And some athletes/coaches are better at interpreting all that data to make the best call for today’s training…
With you on this.
But isn’t it so easy to train before you are ready and perhaps go a little harder than we should 
. Luckily, I’m at an age where I have seen the sense in recovery and using my brain whilst I am training…Trouble is I’m also at the age where I want to know more of what you call “the quest of science based training”. But isn’t there a saying “A little bit of knowledge is a dangerous thing”. Think I’m at that stage now. 
The question: Why would I change things that I have been doing for over a decade?
The answer: Because I’m over a decade older and recovering slower
Once you acknowledge that and if you are lucky enough to have some more time available, you go out more often and/or longer doing lower intensity work and you’re getting better again 
Don’t forget that there should be some form of overreaching, even on LIT workouts. That’s where the signals for adaptation occur.
The body will always want to return to a state of homeostasis, so adding stress will result in the body compensating for it by adapting. The progressive overreaching, followed by recovery, results in super compensation.
It’s a little more complex than that, which is why I like to keep things as simple as possible.
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What are some of the best methods for progressing these z2 (7 zone model) rides?
On fasttalklabs they talk about how they are meant to be much easier than you’d think so I am somewhat wary of doing a progressive overload.
Just keep increasing the watts until you go over the 3-5% decoupling (after a few rides on each increase)?
I also vaguely recall Seiler advocating riding until exhaustion but that intensity would require me in z3.
Simple??? I thought that Polarised training was supposed to be simple…simple, seems like the world and his wife have different ideas of how to perform it . I’ve seen training plans on TrainingPeaks and other websites with intervals that are being called LIT. Ah well, I’ll stick to my understanding as I seem to be producing on avg. 22watts more for the same HR compared with post LIT training after 3 months, so I must be doing something right…I hope 
Extend the duration, and keep the HR below the cap. Even Stephen Seiler says the same, with the both easy and hard rides.
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The boredom factor resulted in so many variations of the same type of workout. I’m quite happy to do the same workout, with progression.
no matter what context, 90m in z1 of three zone model (or 5!) is not high intensity.
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Me too. tried with a film yesterday…boring film though.
My thoughts as well. But I’m wondering if Sleamaker & Browning were thinking along the same lines as Stephen Seilers “Load stress and strain” with 90 min gives too much stress response?
And if you want to quantify it, as opposed to going by feel, then decoupling is an appropriate way to do so – provided that heat, fans, nutrition and fluids are all good.
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If I recall the Endurance training book you mentioned, the authors note that very long LSD rides can leave one tired. I don’t think they intended to say that the rides were “high intensity” as we use that phrase today.
This may be of interest…
This isn’t complicated. 90 minutes in Z1 is low intensity.
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Nice summary. I am going to raise a concern about Seiler’s metric. If you’re dehydrated or fasted, your heart rate / power will rise much sooner than if you aren’t. So is Seiler really saying 60 minutes dehydrated and fasted is just as good a 120 minutes hydrated and fueled?
Maybe Friel has something here. He has said that a workout can be high or low stress depending on the intensity or duration. so z1 for an hour would be low stress, but z1 for 5 hours would be high stress despite being low intensity. Have intensity and stress in this thread become confused?
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All the information is here and don’t overthink it!
Most important is to ride consistent. For me, after a hard race on the weekend a low Z1 ride (5 levels) will actually feel quite hard already after 1h. Beeing more recovered i can do a high Z2 (5 Levels) ride, just around LT1 for several hours and be then of course totally cooked. Still it wasn’t high intensity, I just fatigued the low twitch fibers.
I think the main point is, that over 80% should be done below LT1, so Z2. And if you just do a little racing or fast group rides at least in my case this means, basically always go slow. Over time you get a feeling for the duration and intensity and you know…thats enough.