The winner is actually: “…and thank you for asking”.
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Back on topic, Gordo Byrn tries ISM style with lactate testing:
No warmup, hmm.
FWIW I ‘let the power come to me’ and after 30 minute warmup will consistently see negative split. Here is 68 uninterrupted minutes last week, as part of a 2 hour workout with 100 minutes at endurance pace.
WKO fits a regression line to the data, power (yellow line) goes up +22W and HR only goes up +3bpm, for a negative -5.7% aerobic decoupling. Or said another way, after my warmup at minute 30 I’m averaging around 175W / 138bpm and after 68 minutes its 200W / 140bpm. Roughly. That one had some traffic interruptions early and late, so I pulled out 68 uninterrupted minutes out of a 100 minute endurance interval.
Every Tueday, week after week.
No idea what’s going on with lactate, but what I feel and see in power/HR seems to align with his slow drop in lactate over 2 hours:
That is the endurance work I do 5 days a week, with 2 dedicated sessions a week. But the weekend session is more freeform and harder to extract clean data. Doing that consistently on 8-12 hour weeks.
Back in late 2019 and early 2020, I tried lowering endurance to 55-60% ftp and it only made me better at riding slow. Now its 66-79% with the last third usually around 72%. I’ve field tested that HR, its a pretty good proxy for a challenging but ‘all day HR.’
Everyone has to find what works for them.
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Same observation but I suspect simple thing as volume. If my z2 is limited by 2h, 0.7-0.75 IF is beneficial. If my rides are over 3h this takes it’s toll in overall training, and lowering intensity does the thing. Basically traditional intensity/volume situation and providing good enough stimulus. On the other spectrum of my observations - check out @AlexWild recent training - there is no mercy! 
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I think you are right, I wonder if it’s just the increased volume most of the anecdotal increases are from.
I’ve just done three days of set it and forget it “Z2/LT1/Low Tempo” training. 4:50, 3:10, 2:15 all pretty much bang on.
It’s a great training stimulus, but to be perfectly honest, I don’t feel that different to if I’d done 2hrs at 90% and the rest at 65%.
My RHR and HRV are definitely showing me as being fresher, but Garmin now says I’m detraining so 
Volume matters, I’m sure of it. But I’m consistently at 8-12 hours a week. Last week was almost 12 hours, did a long easy ride on Saturday. 5 hours at 65% IF for most of it, then a long fast downhill and rest stop so IF dropped to 63% by end. No additional fatigue on Sunday, no additional fatigue on Monday, nailing all my workouts this week and raising endurance targets a bit. However I’m feeling a recent fitness bump, so not too surprising.
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That’s fair, and that’s a legitimate reason to use Z2 training.
There’s also many factors that could impact as well including diet, sleep, other stress etc.
Absolutely, increases in volume usually require an increase in lower intensity riding. It gets super hard, I think, to control for the different variables. Especially in anecdotal evidence.
Yeah, wish I was younger, I can do that, but can’t do that consistently. My perspective is that I have a limited “recovery budget” and higher intensity training is taking withdrawals against it. Getting old sucks. Endurance as a first principle has allowed me to consistently raise overall volume and see a lot of gains in aerobic fitness but I’ve only been training for 7 years, no lifetime of base fitness for me.
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I can’t remember if it was this thread, or one of the several other pop up posts from the past week, but there was talk about “brittle fitness” from lack of Z2.
I was listening to episodes of the AACC around 112 the last few days and Chad summarises it super well. It’s not that intensity builds brittle fitness, but you have to pick goals that are relevant to the amount of training you can do.
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That term is in an old Coach Chad blog post from something like 8 years ago when TR changed the long weekend ride to shorter workouts and higher intensity.
I definitely feel the ‘brittleness’ at 5-7 hours/week, versus 7-9 hours/week. But my training age is low, I’m dealing with age related declines, and my off the couch aerobic fitness is a feeble 38 ml/min/kg. With endurance first training its around 46 now, and on a clear path to hit 50. Lots of endurance (7-9 hours/week) and I’m stronger and its in my power curve as well. YMMV and all that.
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- It was mentioned in a couple topics per my searching, but might be the one & following replies:
- Nate said "Sweet Spot Base is not... we shot ourselves in the foot" ...Confused? If the SS Base training isn't SS... What should I do for Base? - #60 by OreoCookie
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I asked him about that. This was his response:
https://twitter.com/feelthebyrn1/status/1623674076521811971
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Random question for you ISM officianados, have any of you run your date through Xert. I see they do a calculated LTP (low power threshold) and I am wondering if anyone has compared.
No, i don’t know how it’s calculated, I also haven’t used Xert in my training. I think it looks like an interesting tool though.
I noodled around with that lower threshold power a few years ago. Totally unrelated. I don’t know how it’s calculated and honestly, that’s part of the problem.
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Your post had me thinking about how much it differers riding inside vs outside.
I can easily 4-5 hours outside, but even a 2-3 hour ride inside at low Z2 will have me feeling it the day after…
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As I understand it ,if your ride above your Xert Threshold Power you deplete your High Intensity Energy and your actual TP decreases. Your LTP is the lowest value that your TP decreases to when your HIE is completely depleted. It is a mathematical construct and generally approximates to broadly where your LT1 is. With me it seems to correlate when I’m on an extremely good day but is generally about 10W higher than my LT1.
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Thanks for that!
It’s interesting stuff.
Volume is definitely a winner for me. Here’s my 2023 stats so far for average weekly duration.
Today I was out 3.5 hours, tomorrow will be about 2.5 hours. Today IF 0.6, maybe slightly higher tomorrow we will see.
Last weekend I had an event and thought I’d see how the legs felt.
It’s quite a good early season event to have a blast on if I feel like it. It’s not a qualifier event, and if I blow up it is no big deal. Felt strong till the end, riding in that in between zone I barely touch in training.
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My reasoning also. A mathematical construct rather than a physiologically based one.
Definitely seems on the high side compared to where I think my LT1 is (based on talk-test - not laboratory test).
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I thought ISM Z2 was mostly continuous and steady-state, not in the form of intervals.
ISM never gives exact prescriptions so your guess is as good as anyone else. On the Peter Attia podcast the prescripton he does give is more for non-athletes wanting to be metabolically fit.
His lactate derived Z2 is probably more like tempo, so it would be quite fatiguing to just do ISM’s version of Z2 all the time. Thus you can break it up into intervals if you like. There are a million ways to slice and dice time at intensity for training.
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