Norwegian, almost to the beat.
(see what I did there)
My LT1 is at about 83% of my LTHR
Exactly. Also its not so much that it matters if you mess it up and get ridiculous results.
Will do
It was interesting to hear the interview with scott Johnston on tts he confirmed my suspicions about the early hr zones. Z1 = La1, Z2 goes up to La2.
I’ve just completed the Skiba book and I see what you mean now. His LT is just above where inflection point definition of LT1. In his words, “you can think of GET, LT, and VT1 to be the same intensity”, but acknowledges a possible difference between VT1 and the other measures based on athlete fitness.
LT = 1mmol above baseline (as @Quaestor stated above). So that is going to be higher than inflection point for determining LT1.
At any rate, he treats anything below ~2 - 2.5mmol to be moderate domain (in the moderate, heavy, severe academic nomenclature). He favors ignoring lactate measurements altogether in favor of field tests and modeling (no surprise there). Also, with training, you “can improve LT from [for example] 70% VO2max to 80% VO2max”. So his LT is definitely not LT1. Although he finds FTP “nebulous” and not equivalent to any actual physiological threshold, he acknowledges its practicality “in cycling circles”. He states: “FTP is probably closer to CP than LT, and would be a reasonable target for long interval training / “sweet spot” training”. Elsewhere I have read he states CP ~5% higher than FTP…but that might have been Andy Jones or David Poole. Can’t remember and someone correct me if wrong. Why care? Because you use an FTP number for pretty much all software or coaching zones, so a valid conversion is useful.
His zones are based on CP, as expected
Periodization
As for Fat util (half the reason we’re talking about all this), he presents a few studies in support of “all good endurance training leads to better Fat oxidation, not just training in a FatMax zone”. It’s duration driven, not affected by intensity differences near FatMax. IOW, .65 IF and .75 IF and .85 IF are all the same. Just do the work.
Now very much interested in looking at this
…as a possible better predictor of performance longer than a few hours (vs CP curve and PD curve, neither of which have addressed these longer durations)
Good summary. I guess I wasn’t going crazy after all 
. The one thing I want to understand now is how is Xert’s model and improvement over Skiba’s (if at all).
Yep, fax max fallacies. My contention with what KM presented (at the time) is whereas there is not consensus that training at/near fat max is necessary to improve fat util (his contention), there is also no consensus AGAINST it (refuting) either. It’s equivocal. We simply don’t know, other than what both sides concede: do a lot of low-moderate intensity. But that is just as much a fatigue management strategy as anything else.
Right, reading all of this would push you back to the notion - one Tim Kusick pushed a few years ago in his WKO webinars - of doing your long rides (3+ hours) in low-to-mid- Zone 2 to limit fatigue incurred from those rides. I think there are gains to be made by including “intervals” of higher intensity (say 10-20min of .7-.75, even up into tempo) a few times in a long ride, but in general when I’m programming long rides now I’m still doing them around .65IF to start with and progress duration first and foremost. If there’s a time crunch and you want to go for 90 min or 2h, then get into the longer .7-.75IF or even pure tempo rides if the rest of the schedule allows it.
. Makes sense. And you’re doing the “cheat” of increasing intensity for duration but in a way that makes more sense than “ok, short on time can’t do long ride I’ll do a Zwift race instead”
And I still zip along at .65 IF most of the time too. Drive that duration out when you can, add tempo if/when maxed out on weekly time or event specific.
But if you start producing lactates in your long easy rides (with efforts) than you will be riding some times on lactates and your fat metabolisation would be decreased.
This intensity inhibits fatox story, I don’t know (dotted lines are actual ox rates, just saying)
I think if you look at absolute fat ox, the rate doesnt really go down much until the crossover point which is slightly above the higher definition of lt1. I think ism likes his prescribed zone because it is good at simulating fat and lactate metabolism.
periodic intensity vs fatox from someone who knows a thing or two about physiology
https://twitter.com/coggan_andrew/status/1497930964063899653
Periodic, sure. What about chronic bouts of intensity? (Probably doesn’t apply to most on this thread but almost certainly applies to many riders)
What are chronic bouts of intensity during a long endurance ride?
Coggan refers to his study where they alternated 15min endurance with 15min at FTP for ~3h. And he saw that there is no reduction of fat ox after the FTP bouts. the opposite acutally since endogenous carbs run out.
I think I heard ISM arguing the other side. But he didn’t specify above or at FTP. So it could be the case that it’s only work above FTP that inhibits the adaptations of endurance work, and they are both right. It would be nice to get clarification from ISM.
Now we’re really running the risk of mixing up different contexts.
Day over day. 3 x week, week after week (or something like that). We see fat ox rates climb back up after the 15min bouts of intensity, but we also have less time at which rider was using fat (preferentially) as a fuel source. Just to make sure I’m understanding correctly, he is not saying fax ox rate was same during the 15min at FTP part. It drops, then comes back up. So overall, we have less fat ox “total time” versus a ~3hr ride with no intensity.
I’m asking (because I don’t know, not because I’m starting a silly internet forum debate): if a rider spends considerably less “time in zone” (at or near Fax Ox), does it matter? To put it another way, is the long slow ride of 4hrs really different than a 4hr group ride? (in terms of Fat Ox).
We do see some evidence that being precise with low-intensity exercise prescription may not be that important:
So overall, maybe it is solely duration-dependent? Just get the work done (regardless of intensity), and fat ox takes care of itself 
If nothing else, it addresses the “hey, coach, did I ruin my long ride by going hard up that hill” question. Likely, you did not.
I don’t have a background in exercise physiology. My understanding is that adaptations are driven by the number of muscle contractions, and very little intensity is required. So duration.
Similar for some cardio adaptations. I’ve even heard either speculation or evidence that the heart may develop “more elastic rebound” by training at lower HRs I dunno, didn’t bother chasing it down on PubMed.
So then the training question comes down to other factors, like managing fatigue from other training/life, and other aspects like for me personally pushing at 70-75% on 8-12 hours/week target makes it either mentally or physically “better” than 55-65%. Better in terms of perceived and measured performance. I don’t know or care if its mental or physical (or both), its just better for me.