PP, HIE and TP relationships

From podcast 2 and from the magic formula Armando put up that seems to relate these three in a range fairly narrow range it is interesting to think what it means to try to improve.

For instance from podcast 2 (pc2) they note that if PP stays constant and HIE increases then TP must decline and vice versa if PP stays constant and TP increases then HIE must decrease. If HIE is an indication of the shape of the power duration curve then higher HIE means you can hold power above TP longer.

All this means if you want to have more endurance above TP (meaning being able to hold say TP+50 watts for x seconds more than currently able to) then you need to increase PP and keep TP constant or allow TP to decline keeping PP and HIE constant. It seems a bit counterintuitive, but that was my take away. Since HIE is the shape of the duration curve then it also means it relates to the rate of decline of MPA, higher HIE means slower MPA decline.

So the way people using other fitness and training systems look at things (and more recenty being questioned) is all about TP or FTP. They have no way to relate to the unique athlete characteristics. I have heard a few recent podcasts talking about the INSYD system and how they look at metabolic aspects related to how you produce power above TP and though not at all a system like XERT it is a nod to the fact that FTP alone is not that informative. Also why Neal Henderson at Wahoo has the 4DP which is basing their system on a power duration approach to fitness.

So focusing only on raising your TP may not always be the best way to improve. Also the signature may mean more than most folks can take in. ie a high TP but low HIE means that person will fatigue quickly above TP whereas a lower TP but higher HIE can sustain that power above TP longer and they are very different athlete types.

Do I have this stuff right @xertedbrain , @ManofSteele ? If not please correct me, I am trying to get this figured out.


Here is something to discuss and explain 3 HIE setting 10, 15 and 20, PP and TP held constant:

see how things differ in how MPA reacts across the various type of intervals. This is something that would be great to explain in some detail.

@ManofSteele @xertedbrain can you help out with a discussion of what we see here?

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Are those intervals based on MMP? I see they’re not the same in each case.

Would be interested to see what you’ve defined.


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Your question is similar to this example showing how HIE differences between two athletes with same TP affects their performance on workouts –
Episode D3 - Mastering Xert - Discover - Fitness Signatures and Conclusion - YouTube

In a nutshell, capacity matters. :slight_smile:

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Ridgerider2 you are the oracle of Xert! I see many question on forum and facebook that do not understand this concept. They do not understand the capacity aspect. In my example however is the situation where in one case the 5 minute interval hit a breakthrough and in another it does not… that is very interesting. ie at HIE 20 the 5 minute interval is not enough to draw down MPA enough15 more so and 10 most, yet it is exactly opposite for the Ronnestad intervals in that case 20 minute hits the breakthrough but the 15 just barely and 10 not at all. So it seems to indicate that 20 is more towards able to sustain extended efforts but 10 is more able to recover and repeat. So HIE effects different effort and recovery intervals in opposite directions. Someone who needs to have longer intervals of supra TP needs a higher HIE and someone who is doing short repeated interval type efforts (crit?) needs a lower HIE? Does that make sense?

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the Ronnestads are based upon 3.5 minute MMP in slope mode, the 5 minute was %TP slope mode. The two early sprints were absolute watts in slope mode, the last 1 minute sprint is 1 minute MMP in slope mode.


Hi @skinner_ron ,

Love the discussion here. I think the final Mastering Xert video that I’ve been working on will be a real treat for you. It’ll discuss MPA in even more depth.

Some things that you’ve pointed out, I wanted to re-highlight…

  • As HIE increases (assuming constant TP & PP), your ability to hold power above TP increases. There are two implications for this for two athletes who have the same TP but different HIE’s. The athlete with the larger HIE will be able to hold a fixed power for longer (e.g. 400 W). Alternatively, their 5 MMP will also be higher.
  • The capacity of HIE influences not only the depletion, but the replenishment of MPA. Larger HIE = slowly MPA decline above TP, but also slower replenishment of MPA (assuming riding at the same power below TP).
    – Threshold Power is still really important, however. While replenishment of MPA is related to the size of HIE, it’s also largely influenced by how far below TP you’re riding. The lower below TP you ride, the faster MPA recovers. e.g. if two athletes have the same HIE, but different TP… not only will the athlete with a higher TP be able to ride harder above threshold, but they’ll also be able to recover MPA faster if both are ‘recovering’ at the same intensity (say, 150W for example).

Hope this helps a bit :slight_smile:


Was going to mention similar points to @ManofSteele but he was much more articulate

Only remaining comment is that to really see the dynamics in those charts, you should use the same absolute power for each ‘scenario’ I.e. no MMP based intervals; just fixed watts (that will also let you play with varying threshold for the same HIE, to illustrate the final point from @ManofSteele ’s post)

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