Seattle Forrest

It's not your ability to absorb oxygen. Might be your ability to deliver it from the air to your working muscles, but the limit is never extracting oxygen from the bloodstream, except in completely untrained people.

redlude97

The reason you can use them essentially interchangeably is that one is the "input" and one is the "output".
Its actually pretty simple biochemically lactate is an intermediate byproduct of anaerobic metabolism


The excess lactate is then shuttled back to the liver to be converted back to glucose in the Cori cycle. You reach a semi-steady state point at your MLSS of ~4mMol.
You can train to be faster before you hit the anaerobic threshold, and you can train lactate clearance and processing at the anearobic threshold, but they are kind of achieved simultaneously

wphamilton

That was my first guess, since it's the simplest, but where does that come from? Or even simpler, you could assume that the control mechanism is a simple function of energy demand.

But, I don't think it is accurate, even approximately, because a) lactate production is not triggered (much) until after the aerobic threshold and b) controls for both of them also involve feedback mechanisms.

redlude97

lactate production is high after the anaerobic threshold because lactate production is the product of anaerobic metabolism, that is why they can essentially be used interchangeably

wphamilton

I was thinking more about extracting oxygen from the air into the blood stream, as much as extracting it out of the blood. I realize that people also say that we have plenty excess capacity in our lungs, but that doesn't make it necessarily true either. Considering how often big lung capacity is a feature of top endurance athletes. Even more likely a limiting factor is getting rid of the CO2 (which impacts the ability to absorb O2)

wphamilton

That's kind of circular reasoning. While I will acknowledge that the first 10 or 20 Google results will define anaerobic/lactate threshold in a way as to imply that, I don't believe that is is very correct. They are used interchangeably only because the interest is setting a threshold number for pace or hr training.

Lactate production rises after the LT by definition, and after the AT because energy demand exceeds the aerobic supply. Two very different things, and very possibly two different numbers under some circumstances.

redlude97

Under what circumstances?The definition of anaerobic threshold that has been widely accepted for over 2 decades is:
https://www.ncbi.nlm.nih.gov/pubmed/3551513
"Lactate threshold" on the other hand doesn't have an accepted definition since its not a clear physiological representation. Your definition above of
is certainly wrong in the context because lactate production rises beginning at aerobic threshold, reaches a quasi-steady at anaerobic threshold/MLSS but continues to accumulate. Now if you want to define "lactate threshold" as the point where the accumulation is no longer linear with exercise intensity which is more accepted then maybe we can have a discussion about the nuanced differences, but the range between the two is barely quantifiable if at all. Once the lactate begins to outpace the clearance then accumulation begins to occur. One causes the other. If you haven't read this article by Dr. Millan, or disagree with his POV as one of the leading researchers in the field, then I don't know what else to tell you
https://www.trainingpeaks.com/blog/w...ate-threshold/

redlude97

No, it is because aerobic/anaerobic metabolism is not rate limited by oxygen consumption, it is rate limited by the speed of the reactions. Aerobic metabolism cannot supply ATP at a fast enough rate at higher power outputs. Aerobic and anaerobic is a bit of a misnomer in this context because its not the driving force.

wphamilton

That's not actually a definition. It's a statement about a quality anaerobic energy, and even for that purpose it is particularly garbled. Literally, it says that oxygen consumption is the threshold, which is nonsensical for a couple of reasons ... I think that you're just trying to argue and found a quote that seemed to help, and I'm not really interested in getting into that.


I'll be blunt here. I didn't ask how to set levels for threshold training - I already knew that, and have already done it. I didn't ask for anyone to explain what AeT is - I already know that as well. I asked if anyone knew how to measure lactate levels in an activity where there is no sensation of it, even indirectly to a single data point such as lactate threshold, distinct from the anaerobic threshold. Rubiksoval thinks they're the same thing. That's fine, and you'll notice that we aren't arguing about it.

redlude97

It is not garbled, because it is defined at a % of V02max, hence the oxygen consumption component.
Even if you could measure lactate levels, you would see that value continue to rise after aerobic threshold, that is the point, and why there isn't a distinction, above anaerobic threshold lactate will continue to rise with time at a given intensity because we have a limited ability to process the lactate byproduct. "Lactate threshold" is a quasisteady state where the amount of lactate accumulation is small because the amount of lactate production is almost balanced a short (<1 hour) timeframe. Furthermore, as explained above, lactate levels do not produce any sensation themselves. You keep trying to find or define these two distinct things when the consensus is that they are close enough to the same thing because one leads to the other. You still haven't provided a situation where you would be able to sustainably operate above your anaerobic threshold without lactate accumulation above baseline.