Only ever seen this referred to in Xert, and even there info about it is only a paragraph. Any idea where this concept comes from or the science behind it. What can you do with the LTP number?
Is it just a threshold where work dine below it is predominantly using fat as fuel?
It’s their term for aerobic threshold, or LT1.. See below. Apparently it is not related to LT1. My issue is that Xert’s explanation of what it actually is A) sounds like pseudo-science and is not practical, and B) sounds like what we think of as LT1 (e.g. “…you can accumulate a lot of strain without materially affecting endurance energy supplies”…<— what are energy supplies? Assuming glycogen, but you have to say that if that’s what you mean).
Oh! Didn’t realise they were the same and that makes wonder now about high high LT1 is. I thought it was somewhere around endurance pace, but looking at Xert it’s giving a pretty high % of FTP for LTP or LT1 as it’s called.
If I’m reading this right I should be able to ride up to Xert’s LTP number and still be within the easy day range for the polarised model?
Pretty sure it would take my HR higher than what I’ve read before about polarised training to even go close to Xerts number which seems to be around 70% of FTP.
Yep, that’s basically the right way to use Xert for polarized training. Easy days below LTP, hard days above TP.
You also need to understand where LT1 is for you. It will be different for many people in terms of the power curve, but is usually about the same RPE between people when using conversational pace. Ideally, if you stay below LT1, you will not get much drift at all. For me, that means almost all of my cycling needs to be within Zone 1 of a 5 zone HR model or <=72% of max HR depending on the length of the ride. When running I can straddle the zone1/2 border and get the same effect.
That’s my issue - Xert is giving a very clearly defined LTP number, and I have a feeling that working even 10 or 20 watts below that number would be too hard for polarised training. But maybe I just misunderstand and that really is alright and recovery is quick enough to hit hard workouts hard.
Xert’s LTP number for me is 15 watts lower than sweet spot’s lower end (going by British Cycling power ranges).
Not so sure after reading the definition Lower Threshold Power – Xert
Lower Threshold Power
Also referred to as LTP , this represents a modeling artifact associated with the depletion of Endurance Energy. As endurance energy declines over the course of a long activity, slow-recovery / long-term fatigue takes hold and Threshold Power, High Intensity Energy and Peak Power decline. The affect of long-term fatigue manifests in reduced MPA and MPA that declines more rapidly. LTP represents the lowest possible value for Threshold Power when all Endurance Energy reserves have been depleted:
If I’m understanding it does it mean then that when you’re wrecked and made an effort to ride at threshold, LTP is what it predicts you could do?
Confused now, really don’t get it 
Kinda reads like “threshold power after bonking” or max sustainable power after bonking (glycogen supply exhausted).
And it’s based on a model, not based on blood lactate or ventilation.
In practice, it’s close enough. (see below with “mimics”
Annoyingly, Xert feels the need to use their own made up jargon for concepts that we already have confusing enough jargon for. When I was in the lab, it was 2 mmol…so whatever that means or is expressed in power meter circles is already going to be an approximation of an estimation. Moreover, “Endurance Energy”. Capitalized? Do they mean glycogen stores? <—— that’s rhetorical. Just making a point. I don’t actually care what they call it because…yeah, anyway
From Xert docs:
In practice, LTP appears to mimic LT1. From a modeling perspective, LTP corresponds to the point at which Endurance Energy is not being depleted and thus does in principle align with LT1 which characterizes the point at which anaerobic energy systems begin to engage in supplying energy to working muscles
(Source: the Xert “polarized vs sweet spot” article)
That’s the way I read it too. Threshold after bonking, or roughly LT1
From a blog post. To my eyes, with the data presented in that blog post it appears to mimic LT1 but is much higher than actual LT1. Even the zone1/zone2 polarized boundary appears a bit high. But I’m not a physiologist or coach that has looked at hundreds of lactate tests 
Like FTP and MLSS. (FTP being the more useful of the two).
Correct. Not sure I follow.
As a former paying Xert subscriber, the lack of documentation was disappointing. And as you said, new terminology is not always a good thing. As they said LTP is a modeling artifact and “does in principle align with LT1” but alignment isn’t the same thing as an approximation or estimate for LT1. Which is just fine, but can be confusing.
Yeah, I agree. I felt the same way.
I was initially excited about LTP from them because it seems more appropriate for the types of events I do than FTP. Without boring you with the details, it was the right idea, wrong execution by me.
I thought LTP would give me insight into why I see performance improvements at longer durations (>3hrs) without a corresponding change in FTP or TTE. It hasn’t. And most folks are (perhaps rightly) just focused on FTP. Not sure I’ll get my answer from current “big names”.
As said before… it’s quite individual, but having LT1 between 70-75% of FTP is not that crazy. Much of the recent interviews I’ve been listening to seem to suggest that it is trainable, so while it can be much lower for some people it can be increased by training to the physiological response instead of a power/pace target. This is a reason for focusing on easy aerobic work, eventually easy isn’t necessarily slow.
How? By improving FTP? (serious question, not trying to be argumentative). Also, improving FTP is certainly one way to do it. No disputing that.
Just read @bbarrera response so let me rephrase qualify my question: besides LSD 
which targets LT1 rather directly
Power at LT1 is absolutely trainable. It is the basis of traditional long slow distance (LSD) base training. I’ve seen a local cat2 put in huge 20+ hour weeks, and by all appearances his LT1 power has gone from 150W to roughly 200W over the course of 1 year.
Agree that LT1 power at 70-75% of ftp is not crazy. I was reacting to the graphic showing LT1 at ~80% although maybe thats common for pros/semi-pros training 20 hours a week?
Maybe, maybe not since LTP are modeled/measured or estimated differently. According to the link, one of the athletes has an LTP 90% of FTP, while the untrained cyclist was around 72%. Both do sound pretty high compared to what actual lactate measurements would say.
Lactate.com has some examples for how quickly some of them have changed their lactate curve relatively quickly. It looks like that can change fairly quickly, but changing the actual anaerobic capacity can take some time.
modeled LTP is always 20+% higher than my LT1 estimate.