How sharp a boundary is the AeT?

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September 21, 2020 at 12:10 pm #45256

JB
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Hi all,

Here is a more conceptual question.

In reading about how to train the aerobic base, which I at least clearly really need, it’s easy to come away with the idea that the Aerobic Threshold is a categorical sort of boundary: If you’re below it, you’re training what you need to be, but if you’re above it, even by a little, you’ve flipped a switch, and now you’re training something else, something moreover that probably isn’t accomplishing what you’re trying to accomplish.

On the other hand, the graph entitled Intensity vs. Lactate in the Physiology of Endurance section of Training for the New Alpinism makes it seem (though it’s clearly just a schematic) as though this isn’t right. This graph seems to be saying that as training intensity passes the Aerobic Threshold, your metabolism begins a gradual shift from mostly lipolysis toward mostly glycolysis. Looking at this graph, you might conclude that training just above and training just below the aerobic threshold are really accomplishing essentially the same thing, and unless you are an extremely high level athlete, for whom it might be important to wring the very last bits of efficiency out of every available training opportunity, then you’re probably not going to notice a big difference in effect on fitness levels and endurance coming from being a little to the one side or a little to the other of this threshold. If this is true, then knowing precisely where your aerobic threshold lies is probably not as critical to your training success as it would be for, again, a high-level or professional athlete.

Which of these two scenarios is more accurate? Is the aerobic threshold more like a categorical boundary, or more like a gradual transition zone, in terms of building aerobic endurance? Or am I completely misunderstanding the issue?

Thanks for any thoughts you might have!
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Posted In: General Training Discussion

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Reed on September 22, 2020 at 1:53 pm #45281

I view it as a model – and “all models are wrong, but some models are useful.” Thinking of the aerobic and anaerobic threshold as on / off switches might lead to false precision, yet there are real physiological differences that lead to the establishment of those thresholds. You’re right, precision isn’t that critical, especially if you take a conservative approach by logging lots of time well below AeT. Make the easy days easy, and the hard days hard.

I recently came across a diagram and definition from the Swiss Olympic federation that I found useful. [1] Below AeT, from lying down to walking to easy running, your lactate levels are pretty flat. Once your lactate rises 0.4mmol/L above baseline, you’re above your AeT. See graph attached. I’ve also seen a rise of 1mmol/L above baseline as a definition for AeT.

Baseline lactate levels that I’ve measured on myself have tended to be in the 0.8mmol/L to 1.3mmol/L range. I’m not sure what that looks like across populations. The AeT lactate figure that I’ve used has been a nice round 2.0mmol/L.

[1] In French, page 28 of https://www.swissolympic.ch/dam/jcr:6ea9b202-857b-4561-81de-bbc799b6b690/Diagnostic_de_performance_manual_160201_FR.pdf

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MarkPostle on September 22, 2020 at 1:59 pm #45283

Jonathan,

I think of it a bit more as the latter of the 2 scenarios you describe here. It is a gradual shift where you go from primarily fat burning to primarily carbs burning as you cross your AeT. If your HR exceeds your AeT by a few beats on a section of uphill it doesn’t magically flip a switch and undo months of careful training. What I like to think of is what is the goal at hand at the moment or for that particular session, if its to build aerobic capacity and that’s best accomplished in Zones 1 or 2 for you at the moment then try and keep your HR at the appropriate level and work towards that goal.
The otherside which you mention here is that while certainly it’s important to have a good handle on your HR zones, maybe agonizing over 1-2 beats one way or the other is unwarranted. One might be better off spending that energy getting out the door and putting in the work!

Participant

JB on September 22, 2020 at 2:30 pm #45287

Thanks both for your responses! That makes a lot of sense.

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Anonymous on September 24, 2020 at 8:55 am #45383

A couple of other thoughts:

Rather than think of a boundary, think of the rate of lactate production. Above AeT, the rate of excess lactate starts to rise faster than the increase in intensity. Your metabolism is less and less efficient as the intensity rises above that point.

Also, I think this is a dangerous, slippery slope:

…you might conclude that training just above and training just below the aerobic threshold is really accomplishing essentially the same thing, and unless you are an extremely high-level athlete, for whom it might be important to wring the very last bits of efficiency out of every available training opportunity, then you’re probably not going to notice a big difference in effect on fitness levels and endurance coming from being a little to the one side or a little to the other of this threshold.

From that attitude, it may be tempting to think, “I’m not an elite athlete, so I don’t have to train like one.” That’s putting the cart before the horse. They didn’t wake up elite and then clean up their training methods. They cleaned up their methods and became elite.

Check out Scott J.’s podcast with David Goettler. In particular, check out minute 18 on the advantage of being specific.

Participant

JB on September 27, 2020 at 6:45 am #45443

Good point, Scott. Thanks!

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