Thanks, I see. So “aerobic base” is really just aerobic fitness? And you achieve it just by doing endurance training?
Same for decoupling - it is just cardiac drift by another name?
Sorry for all the questions. I’m afraid that it has been too long since I took ex phys!
Sorry, one more question. How do the muscular changes responsible for aerobic base alter decoupling? Decoupling seems like more of a cardiovascular measurement to me.
Yeah decoupling is putting out lets say 180 watts fir 30 mins steady and seeing how far you HR drifts higher during that period. Anything under 5% is pretty good.
One little niggle in the article is this antiquated/wrong yet wide-spread metaphor:
Much like a pyramid, our fitness is built in a hierarchal fashion with the initial work serving as a critical foundation that will eventually support a higher peak.
Paraphrasing a logical rebuttal via Emprical Cycling, “Guess you’ve never seen the Washington Monument”, (and other non-pyramidal ‘high peak’ structures).
Sure. Whatever term you use to talk about how efficiently your body turns oxygen into power, it’s that.
There are lots of ways to build it, including low-intensity training. The base plan that TR recommends is mostly “sweet spot” and higher (see that blog post for more of an explanation).
Generally, yes. It’s a different way to measure the same concept: instead of “my heart rate drifted by X%”, it’s “my power-to-heart-rate relationship changed by X%”.
From that TR blog post:
Increased capillarization: more of our tiniest blood vessels which deliver blood (oxygen & nutrients) to the muscle cells and also remove metabolic waste
Increased mitochondrial proliferation: more of the muscle cell components that aerobically process fuel necessary for muscle contraction
Increased aerobic enzymes: more of the catalysts necessary to aerobically produce energy from incoming fuel
My (layperson’s) understanding is that base training improves both the oxygen transport mechanism (cardiovascular system) and the power factory itself (musculature). Anything that alters the efficiency of the oxygen → power process is going to alter your drift/decoupling.
It’s a good question. I’ve not read anything that gives a clear and comprehensive answer.
There have been a bunch of studies showing a reduction in cardiac stroke volume as exercise progresses due to heat buildup and dehydration. And cardiac drift happens as a result. But cardiac drift has also been seen in instances where there is minimal dehydration.
So there may also be a component of cardiac drift being driven by a reduction in a muscles ability to extract and/or use oxygen from the blood. Why might this happen as exercise progresses? Maybe increase in acidity from lactate production reduces enzyme function? Hence the point where cardiac drift starts to happen is correlated with LT1?
Edit: Adding that cardiac drift may also be driven by type II muscles (which are less oxygen efficient vs type I) being recruited as type I tire. More evidence that LT1 is correlated with onset, maybe extent, of cardiac drift. Meaning higher LT1 = less cardiac drift.
Given the multiple things that could drive cardiac drift, hard to know the relative contributions of the underlying drivers for sure.
But I think the evidence is reasonably strong that lower cardiac drift is seen in athletes with higher endurance/aerobic performance.
@DaveWh and @old_but_not_dead_yet this is the best article I’ve bookmarked on the science behind decoupling, with explanations on what is likely going on when HR rises during steady-state exercise:
Alan Couzens: The Science of Decoupling
“In fact, type II fibers require ~twice the O2 for a given power output. Therefore, small fiber shifts result in relatively large differences in heart rate for a given power output (Coyle, 1992)”
I didn’t know this. Wow - that’s a huge difference vs type I.
I’m doubling down on my SS training during base. Convert some of those type IIs!
For other important reasons too:
during exercise lactate is mainly produced by [type 1] glycolytic fibers…However, lactate is mainly cleared by adjacent [type 2] slow twitch fibers…
“Aerobic base” helps with a lot of stuff. 
Not sure where you copied and pasted from, but slow twitch are type 1 and fast twitch are type 2
On z2 rides I usually experience negative decoupling (> 5%), i.e. lower hr in the later half of the ride, any theories on that? I might add that I’m more of a sprinter so probably primarily fast twitch fibers.
It sounds like a gross exaggeration to me. If it were true, wouldn’t you see huge differences between people in oxygen update at a given power?
I haven’t had the chance to review the source papers for the 2x data. I’m not surprised there’s a difference. 2x does seem high though.
consider there might only be a small shift. Couzens references this 1992 Coyle/Joyner article: Endurance exercise performance: the physiology of champions - PMC and I couldn’t find the full article. However the following year Coyle published this article: Cycling efficiency is related to the percentage of type I muscle fibers - PubMed and I did find a PDF of it. Paraphrasing the summary:
And from page 1:
Hope that helps.
So now we’ve gone from a 100% difference to a 9% difference? Which are we supposed to believe?
without context you can make up all kinds of great stories with incredible sounding numbers. To my eyes the Couzens blog is an exercise physiologist talking to other physiologists. He didn’t fully run another set of numbers, instead he commented based on general principals. I guess the moral of the story is - don’t extrapolate if you don’t have context? 
That’s part of the evaluation process - find a bunch of papers, read them, triangulate, and come up with a conclusion. It’s time consuming to do for a layperson - especially with research papers like these that have a bunch of arcane medical terms. People on this forum invest a lot of their time trying to sift through stuff like this. 9% or 100%? I’m more inclined to believe 9% but I have read the sources yet that @bbarrera has linked to.
You have to at least think about it the right way. People don’t only have Type I or Type II, they have a mix. Let’s say Type I fibers use 1 unit of oxygen and Type II fibers use 2 units of oxygen, and then let us say that each fiber produces 1 watt and we are limiting each group to use 120 units of oxygen. The muscle fiber recruitment would look like this:
Group 1: 73 Type I, 23.5 Type II => 96.5 total muscle fibers
Group 2: 48 Type I, 36 Type II => 84 total muscle fibers
From this MASSIVE oversimplification we would see that group 1 would produce 14% more power. Obviously the assumptions made here are egregious, but once you frame things this way you can understand that we should not expect some people to consume twice as much oxygen at a given power output.
and to continue the example, here is oxygen usage:
Group 1: 120 units of O2 (73 + 23.5 * 2)
Group 2: 120 units of O2 (48 + 36 * 2)
Same oxygen usage, but group 1 has 14% more muscle fibers contributing to power output.
But what this brilliant calculation shows is that both the 9% and the 2x numbers can be right.
