Are power zones stable over a longer workout?

Can anyone speak to whether power training zones, as defined by the combination of adaptations achieved by working in that power range, are stable over the course of a big workout, or do they drift with expended effort like the relationship between adaptations and heart rate zones does (“cardiac drift”)? For any runners out there, this question is for running pace zones too!

Obviously there are caveats here about eating and hydrating before and during the workout properly. But specifically my question is [using Coggan’s tables] whether the relationship between power zones in table 1 and the marginal physiological adaptations gained from doing marginal work in the power zones from table 2 is the same at the end of a huge ride - say, 300+ TSS - as it was in the beginning?

I could see a few different possible answers here;

  1. Proportions of adaptations and the power zones they’re derived at are both stable. End of story.
  2. Proportions of adaptations are stable and the power zones they’re derived at are stable, but after some level of expended effort the returns-to-effort within that zone start to taper. This would probably happen fastest at the highest zones.
  3. Proportions of adaptations are stable, but the power zones they’re derived at drift slightly with expended effort.
  4. The proportions of adaptations at most (if not all) power zones derived from additional work within each power zones changes with expended effort
  5. Nobody knows, but why are you targeting specific adaptations after 300+ TSS?

Power “zones” are stable regardless of a single workout because they were never firm in the first place:

First, it may be a bit of semantics, but Dr. Coggan calls what you are referring to as zones, as levels. Part of the reason he has said that he does so is that the original way to train was based on heart rate “zones” where the boundaries were rigid. With power, the delineation between levels is more fluid and, in fact, as he states, the # of levels itself is somewhat arbitrary.

Second, the establishment of one’s FTP, from which power levels are determined, is not exact. Since maximal lactate steady state (MLSS) can’t be practically determined in real time, “field tests” are used to determine it. And as you probably have already learned, there are many “FTP Tests”, including the 8min, 20min, 30min, 40min and even hour power with several protocols of each. Oh, and yes, even TR has come with its own . . . the Ramp Test. None of these test can definitely claim to be one’s exact MLSS inflection point (the point at which lactate clearing becomes non-linear) and thus, are only estimates of one’s FTP.

For further information, I might suggest that you listen to the WKO4 webinar with Dr. Coggan and Tim Cusick when they discuss Coggan Classic Levels (the 6 zone model) and the Coggan iLevels (the 9 zone model). Power-based training, as invented by Dr. Coggan, is very powerful, particularly as you gain a deeper understanding of several of its key metrics, including NP, IF, CTL, ATL, TSB, TTE, and FRC. But as Tim and Dr. Coggan discuss, a common mistake by users is to take the boundaries too seriously and should more focus on the overall desired adaptation at each level.

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What you basically seem to be asking is “what is the purpose of training when fatigued?”

My understanding is that there is little purpose to it, except to test your ability to perform when fatigued. The following blog, for example, talks about how a good test of a junior GC rider is their ability to go for 20 minutes at 5.5+ w/kg after 3000 Kj of work.

However, that doesn’t mean he would necessarily spend all his time riding for hours and then doing threshold intervals. I imagine most of the hard work would be done when fresh, when the body is most ready to complete the work, absorb, and adapt.