yup that seems to be it, I think you are correct. Thanks
Do you actually want more time x% above TP (eg the 150% you mention), or just more time at a given power eg the power your fitter group riders are putting out? If you increase TP you’ll not need to go so far into the red to keep up, so you may only be holding 110% of TP or even riding at TP for those same absolute efforts
And presumably long ride endurance means ‘long ride at high power’ where again a higher TP (and LTP) would help? So overall you may be better off lowering HIE and increasing TP / LTP depending on objectives (noting there’s a trade-off). That’s where you’d look at focus and rider type?
You could use the workout builder to play with interactions to get a feel for it. Build a workout alternating between 400w and 200w efforts (or whatever interests you… something that is close to your group ride pace lines maybe) for whatever durations you’re interested in (eg 2 min on, 2 min off), then play with signature in that workout and see what’s required to make it do-able? You’ll see it’s not just higher HIE that improves ability to hold and recover from 400w efforts
Beyond the MPA Modelling, I think this one is about repeatability or fatigue resistance, linked to the holy grail Armando refers to, which is yet to be cracked by anyone? I guess higher training load and practice doing specific intervals will help with that though. And difficulty score helps give an idea of do-ability for shorter rides, even if the longer ride fatigue is not yet fully modeled…
Thanks for the reply, on the first question it can be a lot of things: ie lumpy course so need to go 150% of TP to get over the climb and stay with the group
it can be inconsiderate people who when they hit the front of the pace line pick the pace up 10%… if one is at or near TP then we are talking 110% of TP roughly
the endurance thing is slightly different,
in the upper case you are jumping then resting then jumping and resting over and over that is it seems a different sort of endurance (ie the ability to recover)
vs the latter which is just a high pace for a long time ie at, near or over TP… more just a relatively stable output but at a high effort for a long time… or a less than TP say LTP effort for a longer time…
So what I an trying to digest is the best way to understand my signature and how it relates to the different scenarios above. When your HIE is high what does that mean and what is actually a high HIE? Is there a relationship between HIE and TP that helps understand how they relate to the different types of efforts above?
As far as I can tell PP is only a means of determining you MPA ceiling, ie it is your maximum power output and thus MPA must decline from that number. However the rate of that decline appears to be a factor of the amount you exceed your TP. Also when MPA falls below your TP you have theoretically exhausted your power reserve if your signature is correct, you should bi e in a state of failure at that point and must start to recover.
I sort of maybe get the principles of XERT and as Armando said above HIE is kJ and “The more kJ you have, the longer you can hold power above TP” but nothing seems to tell me the rate I burn up hose kJ and I guess that may just be the way it has to be until we reach the holy grail. My physiology seems to be better at short repeated efforts then long hard efforts. I can definitely get a breakthrough with repeated short hard efforts with short (about 30 sec) rest intervals say 3 hard (150% TP) then one really hard (say start at 200% TP and hold as long as you can) and I can almost guarantee a breakthrough will happen. But try to hold 125% of TP and I can not get MPA to decline before I am unable to continue…so that is the equation I am trying to crack.
“[4000 words] …so that is the equation I am trying to crack.”
You’re trying too hard. Go ride! 
When one is trying to gain understanding there is no such thing as trying too hard! But I do still have a good time riding my bike regardless if I understand XERT or not! <40 words;-)
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On this one, if Xert’s modeled power doesn’t closely align with what you can do (when fresh, motivated etc) it is possible that your signature is not dialed, and it maybe worth getting support to take a look. The algorithms are not always perfect (and / or maybe they’d say the data going in is not always perfect 
)
On a related note, I recall @GoustiFruit had issues holding 95% of TP for 4x8 minutes per previous forum posts (see front load periodisation ones), despite being able to have a BT on Ronnestad style efforts. Not sure if that was ever clarified but sounds similar to what you are seeing.
I’m pretty sure that there is something wrong with Xert’s algorithms or model to generate the signature: I’ve been doing lots of HIT workouts during the Winter, with very low volume; so, yeah I was able to finish workouts with short and intense intervals, but I lost A LOT on the side of the endurance, so it was a real pain to hold power around threshold for more than a handful of minutes ! I guess that it’s very inaccurate to evaluate a TP solely based on the ability to do short intervals. Being able to push some watts for a short duration, doesn’t relate to the power that you are able to sustain for long periods.
It’s like comparing bodybuilders to endurance cyclists: sure, bodybuilders can push a lot of watts… on explosive efforts. But they wouldn’t be able to follow the average cyclist on his Sunday easy ride.
Reminds me of some of VC’s videos
So, I don’t know how the HIE relates to this. I think that there must be at least a fourth variable to make the model more credible. It should take in consideration the volume that you accumulated through your training period.
At least, my training this Winter made me realize that, yeah, volume is a primordial parameter for someone who wants to improve his TP. HIT won’t help you on long intervals, it will only improve the explosiveness, and maybe the repeatability of short efforts. But if you can’t hold a good percentage of your threshold power for a long time, your HIE is mostly useless.
My conclusion: I’m going back to the work on longer rides, starting with focus around LTP, then some TP intervals, and I will try to keep doing some HIT sessions here and there to maintain the (relative) power I got this Winter on shorter intervals…
Gousti, I agree with you totally. In fact I have been looking at W prime to see if I can get a clue… I know Armando will say they are different and that may be so but the research in this area has found that the rate of use is fairly universal (at least that is how I interpret the papers) but the replenishment is very individual. The have introduced a replenishment factor called Tau W. This is a personal variable. Skiba et al and others have done work on this. He has examples where the replenishment rate would suggest at certain wattage relatively impacts the time to replenish. (Understanding Work Above Threshold) and the rate is quite different from XERT’s. " It turns out that the relationship is defined by the difference between CP and the recovery power. Thus, a person with a CP of 300W will recover more quickly when they drop to 20W than a person with a CP of 200W. In the former case, the person is recovering 280W below CP. In the latter case, the person is recovering only 180W below CP. This helps explain why great athletes seem to recover so quickly." so that might be a clue? Personally I have always been good at short hard effort, but do not have super high PP. Currently like you I have poor long duration power endurance and that is what I am trying to focus attention on to improve. (lots of words this time 
)
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That is what I exactly try to do @GoustiFruit ! Endurance, Climber, then some HIT once in a while.
And I have the exact opposite issue regarding breakthrough! I have lots of difficulty achieving breakthrough using high intensity (intervals), but no issue at all doing it on FTP test. I find FTP test much easier to do than high intensity.
Eventually, we’ll reach in the middle…
I hope 
I started a new plan by the end of April, beginning with a Pre-base phase, then Base phase, with mainly endurance rides and a couple of higher intensity workouts each week. Doh, and I switched, a couple of days ago, to the new “Continuous” plan. For now, I feel better on longer endurance intervals. For ex. I was able to do a 4x8 min. workout last Saturday, and I was not as exhausted as I remember a few months ago on the same on workout. In fact, I was quite happy with how I felt after that workout, I think that I could have gone a little bit harder
I am back on this topic again… @xertedbrain or @ManofSteele is there a way within a training regime to improve HIE? If HIE relates to some aspect of the ability to sustain efforts at above TP then the higher the HIE the longer you should be able to sustain high power efforts… is that correct? So if you want to improve the ability to sustain and repeat efforts at 150% of TP what would you suggest as a best practice?
thanks for bringing this topic back i hadn’t read it and find it a good topic…
so we can only really assume our power/MPA that we see on the Garmin is correct if we’ve been optimally replenishing our carbs during the ride?
and if we aren’t replenishing our carbs, then the fat/carb measure gets off since our real-time signature has degraded (IE we are starting to bonk)
if we don’t eat carbs, then we start burning more carbs due to the degraded fitness signature, and ultimately it’s a vicious cycle…
it appears that if we burn more carbs with higher HIE, then the carb oxidation rate becomes elevated at lower wattages relative to the TP and LTP… the shape of the curve just changes…
does the ratio of fat to carbs also change at TP when verying HIE? someone with HIE could then be expected to not be able to go as long at TP before exhaustion because they use up muscular glycogen and are not able to efficiently digest carbohydrates to keep up with that demand… while someone with a low HIE, burns more fat at TP and can thus go much longer?
Yes.
Also yes.
This is one of the contributing factors to varying Time to Exhaustion at threshold power.
And something else (just to point out) is that simply having the carbs, whether as glucose in the bloodstream or glycogen in muscle/liver tissue, isn’t the only issue. You also need to be able to process those carbs into lacate, and then further be able to process the lactate (either burn it aerobically in the mitochondria or distribute it to other cells across the body). If your ability to breakdown carbs/produce lactate or your ability to effectively process that lactate isn’t there, having a massive store of carbs isn’t necessarily very helpful if you’re trying to produce power near/over Threshold. This starts to tie in the idea of VLamax (the max processing speed of glycolytic system, measured via production of lactate).
Clear as mud, right?
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Specificity. XATA does this automatically as part of the 120 TED program type. As you draw closer to your event, your training should increase in specificity - e.g. the strain accumulated in workouts/activities should more & more closely resemble the strain you’ll encounter during your event.
FWIW, while there are certainly parts of the power duration curve that are more influenced by HIE, but there is no training ‘just’ HIE. You cannot accumulate high strain (XSS) without also accumulating low strain (XSS). In fact, your ability to perform at any effort is always some combination of PP, HIE, & TP. And this is exactly why we introduce the concept of FOCUS, which helps us to understand the relative contribution of all 3 systems to any particular intensity.
We avoid the use of %TP because its so variable across athletes, especially for such high intensities above TP. It would be better to summarize it as a focus duration. For example, where does 150% TP fall on your PD curve - I suspect that’s somewhere near 2-3 min. To improve that, then focus (pun intended) on workouts/activities that provide a mixed (ideally pure) specificity and a focus duration of ~3:00 (Pursuiter). Pursuiter, Puncheur, and Breakaway Specialist (3, 4, & 5 min power) are all great Focus types for improving your supra-TP abilities. HTH!
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Thanks Scott as always very helpful!
I’m going add my question to this topic …
If you are focusing on increasing LTP, is there a case for training specifically to lower HIE? I think Steve Neal hinted at this in the last podcast, although I might have misheard. I am guessing that HIE could be treated like VLAMax, and to lower that supposedly you do specific training like low cadence tempo.
Indeed as HIE increases, LTP decreases and vice versa. Think of HIE as “capacity to burn carbohydrates and generate lactate”. If it’s too high, you will use this capacity at lower intensities which may be counterproductive for very long events where the goal is the reduce the use of carbohydrates at lower intensities.
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I recall hearing Sebastian Weber saying on a podcast. As big a VO2max as you can get and an appropriate Vlamax for the event you are focusing on.
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one aspect of all of this is how you generate a breakthrough to get your signature. I find that for me if doing an indoor workout this is my favourite option
it seems to hit multiple aspects and any one of the 3 or 4 spots in the workout may generate the breakthrough and it can also tell me which type of breakthrough it is , ie a short punch, or longer duration. All of the intensity sections are performed in slope mode.
I appreciate any feedback on this workout and thoughts on what a breakthrough at different points in the workout might mean? I typically only get one point where MPA hits actual power long enough to generate the breakthrough.
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I like the look of this one… makes a ton of sense! I’d like to try it… Are you able to share?