AeT, Lactate, and Fe02

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February 28, 2021 at 3:27 am #51342

dalisinferno
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Hey all

Hope you’re doing well!

I had a quick question aboutabout measuring Aerobic Threshold.

I recently did a lactate test, that included some measurements around ventilation.

The lactate component (graph 1), showed a lactate reading of about 2 at 160BMP. Based on my understanding, I could treat this as my AeT threshold.

Another graph provided, however, showed a big spike in fraction of expired oxygen (Fe02) at around 135-140 bpm (Fe02) – it seems that my aerobic function reduces a bit at this point.

The tester suggested that my AeT is probably around 135-140 due to this, even though lactate levels are quite low. I just wanted to ask if anybody had any experience in interpreting results like this and had suggestions on how I can treat my Z2 / <AeT training going forward.

Thank you!

Lenny

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Posted In: General Training Discussion

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Reed on March 1, 2021 at 11:02 pm #51434

Can you describe some details about the warmup and the testing protocol? The interpretation of the gas exchange test may be fine by itself, but the high starting lactate readings give me pause. If the warmup was insufficient and / or the ramp rate was too high, the ability for the aerobic system to contribute sufficiently might have been limited.

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Anonymous on March 2, 2021 at 9:16 am #51438

Reed is correct to be concerned about the high initial lactate reading. Were you fasted for this test…..Or had you just eaten a Snickers bar?

When blood sugar levels are high the default metabolic process will be anaerobic glycolysis which will give high lactates. Once you got rolling though your lactates exhibited a normal decline and then increase. At HR=146 there is a distinct upward trend beginning. So I’d say that somewhere in the low to mid 140s is the AeT.

Looking at the FeO2 graph is also interesting. The normal range for FeO2 (Fraction of expired O2) which is a measure of the amount of O2 still left in the air you exhale. At Seall level air is roughly 21%. Since aerobic metabolism uses O2 you’d expect that there would be less O2 going out than coming in if aerobic metabolism is the main ATP producer. Normal FeO2 levels are from 15-18% meaning that we use between 3 and 6% of the O2 we inhale for aerobic metabolism.

Your FeO2 levels are quite normal looking. I suspect the drop in FeO2 (increased O2 use) at 135 is coming from a sweet spot in economy. Do you do a lot of your running/hiking at this HR?

In the end I’d still feel quite safe in suggesting that you use mid 1402 for AeT.

I hope this helps.

Scott

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dalisinferno on March 2, 2021 at 9:48 pm #51456

Can you describe some details about the warmup and the testing protocol? The interpretation of the gas exchange test may be fine by itself, but the high starting lactate readings give me pause. If the warmup was insufficient and / or the ramp rate was too high, the ability for the aerobic system to contribute sufficiently might have been limited.

The warmup was quite short – the data you see is the entire test, inclusive of the warmup. I think, next time, I will do a more gradual warm up. The tester said that high starting lactate is normal (perhaps due to anxiety around the pin prick?)

Thanks, Scott! I was fasted when I did the test. I actually do the vast majority of my work in the 130-135 region, so that seems to make sense.

That was very helpful, appreciate both of your comments!

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dalisinferno on March 2, 2021 at 10:11 pm #51457

Just some details about the test. It was about 25-30m in total, starting from a walking pace and increasing incline + speed every 3 minutes (With lactate being taken at the end of each 3 minute window). The first lactate reading was taken about 30 seconds after I started walking on the treadmill as a baseline.

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Anonymous on March 4, 2021 at 8:44 am #51550

The tester said that high starting lactate is normal (perhaps due to anxiety around the pin prick?)

Umm… I would not use that lab again.

Either the tech is new to this and/or hasn’t seen (m)any tests from subjects with strong aerobic systems. Whatever the reason, it suggests inexperience.

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dalisinferno on March 5, 2021 at 12:55 am #51577

Do you have a suggestion as to why the curve started high, only to drop over the following period?

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Reed on March 8, 2021 at 7:54 pm #51749

It started out high for some reason or another – perhaps recent carbohydrate intake, as Scott mentioned. As you started to move, your muscles started to pick up the pyruvate / lactate for use as fuel. The more important thing, though, is that it sounds like you didn’t have a sufficiently long or gradual warmup to give a very clear picture of your aerobic and anaerobic thresholds.

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