HIE understanding

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?


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?


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!


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.

1 Like

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.


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.


I like the look of this one… makes a ton of sense! I’d like to try it… Are you able to share?

I would if I figure out how to share workouts. It is very simple, the red parts are all in slope mode so that you are doing it by feel and target. I will bump around trying to figure out workout sharing but if anyone know how let me know. It is odd that I can download other formats but not an Xert format then one could import and Bob’s your uncle! Also no obvious way to attach files to the forum posts? it will not permit this file format attachment…

1 Like

You could create a community within “coaches” and share it there.

You could add SHAREME to the description. And then it is in the “Shared Workout Coach Community” that people need to joint to see it in their Coach workout tab.

1 Like

And then just let us know the name of the workout.

OK try this: 3DP- test SHAREME

Sufferfest workout?

I would say the higher your HIE the more likely you’ll make it through the entire workout intact. :slight_smile:
The last interval will definitely test your ability to perform under fatigue which brings up a potential issue.
Depending on your TL and experience with BT workouts in slope mode, I’ll bet some first timers might be cooked before the ending effort. If you got a BT already that may be the only max effort you’re able to muster (which is fine). If you pull off multiples, I hope a bump in HIE is in the cards. :+1:

This article details the different ways to produce a BT and what’s most likely to change signature-wise –
Breaking Through the Xert Way! – Xert (baronbiosys.com)

The early sprint efforts determine whether you can exceed your Pmax (unlikely indoors). That would be a push-over BT. The others are pull-down BT efforts with the second and fourth at different MMP intensities. The third has the potential for multiple BTs using a set of Tabata/Ronnestad-style intervals. I like this type of BT effort but do best when on a group session as I’m more likely to talk myself out of “one more” on my own.

Also of note is this snippet from the Academy series –

For those unfamiliar this snippet explains how BT circles are coded by color and size on your XPMC chart –

As far as sharing goes, a few years back Xert was asking for submissions and those deemed worthy were considered for inclusion in the Standard library. Not sure if they are still doing that.

sort of, modification of the 4DP ride, without the 20 minute segment… added the Ronnestad type segment instead… so I altered it to an Xert version with some intervals based upon MMP as the target power but in slope mode. Just one I like because it hits a lot of different types off efforts in one round and if I play it right I get through without failure. It is a really good test and whether you are a draw down BT person, or a repeated effort BT rider it should work.

1 Like

Thank you, that clarifies a lot.


1 Like