AeT Thought Experiment | Uphill Athlete
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• #31125
depeyster
Participant

I really like the DIY Anaerobic Threshold Test because it is a direct measure of maximum output for a given period of time (in this case 30-60 minutes). Unlike gas exchange or blood lactate it’s at the level where the rubber sole meets the trail.

If cost, convenience, practicality, and safety were not a concern, it dawned on me yesterday as I was doing my long hike, that I ought to be able to conceive of something similar for AeT.

In his article on ADS, Scott Johnston wrote:

. . . if you’re training for an event over 3 to 4 hours in length, like a big alpine or mountaineering climb or an ultra-distance race, then the basic aerobic training is the event-specific training and the base training all rolled into one. That’s because the intensity you compete or climb at—your race pace or event-specific speed—is your aerobic threshold. In these longer events, your aerobic capacity is a direct measure of your event-specific endurance.

So, I did a thought experiment. Suppose I had a treadmill with no time limit (in real life I only have access to treadmills in commercial gyms where the maximum duration is either 30 or 60 minutes). My AeT pace would be my maximum sustainable pace of x minutes, where x might depend on my objective.

When you read the journal articles, they sometimes use time-to-exhaustion (TTE) measures. The DIY AnT test is a variant of a TTE test. In the AnT test, pace is held constant and average HR is measured.

The procedure:

1. After a rest day, pick an HR as a candidate for your AeT value.
2. Warm up on an inclined treadmill for 15-20 minutes until you are at your AeT HR minus 5 (to account for subsequent drift).
3. Stay at the incline and pace attained at the end of step 2 until you reach exhaustion (i.e., you are unable to continue).
4. Record the TTE and the average HR (both measured from the end of the warmup to the test’s end).
5. If TTE> 3-4 hours, then you were at or below your AeT.

That’s the thought experiment.

It left me with some questions.

1. Wouldn’t it be better to run the test for 8-10 hours or even longer, if you wanted to be able to spend long days in the mountains?
2. If, in the real world, you had to stop and restart the treadmill every 60 minutes, would that distort the results appreciably?
3. Why not chart TTE at a series of intensities and graph them? The AnT is TTE(.5-1h). The AeT is TTE(3-4h). Right now ADS is defined as a >10% gap between AnT and AeT. Seeing the shape of individual TTE curves might shed light on previously unknown relationships.

• Participant
depeyster on #31126

Correction:

Question 3 at the very bottom:

3. Why not chart Pace-to-Exhaustion (PTE) as a series of intensities and graph them. The AnT is PTE(.5-1h). The AeT is PTE(3-4h). Right now ADS is defined as a >10% gap between AnT and AeT. Seeing the shape of individual PTE curves might shed light on previously unknown relationships.

Participant
todd.struble on #31129

During my last DIY AeT test, my mind was also wondering about very similar questions, so I’m super interested to read what the experts have to contribute, so I hope you don’t mind my piggybacking on your thread.

My question was a bit more generalized for the 1 hour test – why exactly one hour and 5% drift? I suspect the answer is two fold – 1) Scott J. has written in their experience 1hr/5% drift provides a 95% confidence that the result is accurate and my guess is that’s probably “good enough” for training purposes; and 2) 1 hour at low intensity is easily repeatable. You could test every week and it likely wouldn’t impact your training that much. An 8 hour test might be more accurate but I sure as heck ain’t doing 8 hours on a treadmill or around a track even once. I get bored after about looping the track after 15 minutes! That would also be (for me) almost my entire aerobic volume for a week in one workout and take a few days to recover from.

But it does beg the question – does a 3% or 4% drift result provide a higher confidence? Would your longer protocol provide a higher confidence if we wanted to do a longer test?

Participant
depeyster on #31303

Rereading some of Scott J’s posts, it seems clear to me that a 3-hour TTE test at a steady pace would provide a good approximation of AeT.

For example:

. . . consider the marathon. This event is competed at an individual’s aerobic threshold or just a tiny amount above that. So, minimal involvement of the anaerobic system. This is true for someone running a 2:05 race or a 4:05 race. That 2:05 marathoner can sustain a pace of 4:45/mile for 26 miles relying 95% on his aerobic system for energy.

The trick is to know what pace to begin the test with so that exhaustion is reached within 3-4 hours.

@todd.struble I think that Scott J. has always been clear that nothing is written in stone. The HR drift does not require *exactly* 30-minute laps and you don’t need *exactly* 5% drift to determine AeT. Our bodies are not machines and a phenomenon as complex as AeT–which is the product of processes occurring at many different levels and in many different locations–cannot, in reality, be totally understood with a single number. It’s a ballpark.

The whole reason I would like an actual test of my long-term TTE is that my Gas Exchange Test was clearly wrong. My RER 0.85 crossover point was 164-167 bpm. There is no way I can hold that HR for very long. That test was done in June this year when I was 63 years old. (When I was 62 years old I did a HRmax test with a chest strap monitor and reached an actual HR of 178 bpm on an elliptical machine.) I don’t think the gas exchange tests work the same for low-carb high-fat (LCHF) athletes. If you look at the FASTER study, which Steve and Scott cite in TFTUA, their elite LCHF athletes did a 3-hour bout at 64% VO2max at RER of 0.73-0.74. The balanced diet elite athletes had RERs of 0.86 at rest. I could not find their exercise RERs in the journal article.

I eat LCHF, so it makes sense that my AeT would occur at a lower intensity than my 0.85 RER. (I don’t eat LCHF for performance reasons but, rather, for other health reasons.)

Since my Gas Exchange Test did not give me a solid basis for deciding my AeT, I then did a few HR drift tests. On October 9, I had an average HR of 152, followed by 156. But, realistically, I can’t imagine going higher. I can’t even imagine going 3 hours starting at 152. When the HR drift test ended I was happy to be done and I would have been very unhappy if I would have had to repeat it the next day. These sentiments suggest to me that I was going higher than my AeT.

So, I am very tempted to spend a long Saturday in the gym starting at, I don’t know, 142. I’ll bring a bottle of water, perhaps, and see how long I can continue, taking breaks for a minute or so every hour to restart the machine.

I am thinking that a lot of the limitations that could be present in indirect tests (gas exchange, lactate, HR drift) could be eliminated by a direct TTE test. Of course the TTE test has its own limitations, being both inconvenient and disruptive. But it also might give the best approximation of AeT.

And from my understanding of everything written by Steve and Scott J., nothing is more central to effective UA programming than an accurate value for AeT. It really is the key to the UA paradigm. (I welcome all criticism of any and all of my ideas. You would be helping me improve my understanding of this.)

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Participant
Michaeltyoung on #31349

The PTE curve you’re describing is a concept discussed and constructed in cycling, where doing all-out-efforts of a given duration can be pretty quickly recovered from (see https://www.trainingpeaks.com/blog/4-key-uses-for-the-power-duration-model/). But even in cycling, I think the curve is mostly constructed to estimate PTE for periods shorter than an hour. The idea of trying to PR a marathon just in order to estimate your AeT so you can train better doesn’t seem worth it given the amount of recovery that a ~3 hour effort will incur.

It’s possible that your inability to sustain what you’ve estimated as your AeT is due to muscular limitations. Scott has mentioned that for very aerobically fit individuals, training at AeT incurs a high recovery because of neuromuscular demands and that athletes in this situation need to train mostly in zone1 (rather than zone 2) with some zone 3/4 to push their AnT higher.

The overarching question you’re asking seems to be “what intensity should I do most of my training at?” It seems that you have your answer right here:
“When the HR drift test ended I was happy to be done and I would have been very unhappy if I would have had to repeat it the next day.”

The most fundamental way of determining base intensity is identifying an effort that you can 1) recover from in 12-24 hours and 2) maintain a high volume at that intensity for weeks to months without breaking down.

If your estimated AeT doesn’t fit those criteria, then find an easier effort level that does.

Participant
pshyvers on #31374

I really like the DIY Anaerobic Threshold Test because it is a direct measure of maximum output for a given period of time (in this case 30-60 minutes). Unlike gas exchange or blood lactate it’s at the level where the rubber sole meets the trail.

I ought to be able to conceive of something similar for AeT.

In a sense, that’s what the AeT treadmill test is. The maximum output you can sustain for a given period of time- with your mouth closed. There’s obviously some variance depending on how well your nose functions, but (after I got my nose fixed) I was pleased & surprised how quickly I went from “I could do this all day” @ 162bpm to “oh my god I need AIR” @ 165bpm. It was nowhere near as subjective as I thought it might be.

Participant
depeyster on #31429

@Michaeltyoung
Thanks for that fascinating Training Peaks link. It’s interesting that both TP and UA run time-to-exhaustion tests, but only up to an hour in duration.

I agree with you that doing a ~3-hour time-to-exhaustion test has some real health risks. That’s one reason why I framed it as a thought experiment.

I found your following point decisive and undeniable:

The most fundamental way of determining base intensity is identifying an effort that you can 1) recover from in 12-24 hours and 2) maintain a high volume at that intensity for weeks to months without breaking down.

The question for me is, what happens if we find out, months later, that we were too high or low? Wouldn’t that kind of overtraining have effects much more insidious than a single 3-hour bout? If we were undertraining, the harm would be less. But we might be sacrificing potential gains.

If you did the TTE with planning, you could program adequate recovery before and after.

@pshyvers
I am not sure which “AeT treadmill test” you are referring to. I’ve never had to mouthbreathe during my HR drift tests. But, I found those test unpleasant and uncomfortable. It just felt like I had to push myself pretty hard. As I mentioned, I was glad when the two 30-minute laps were done and I really would not have been happy if someone told me I had to repeat the test the following day. I think that Scott and Steve said that breathing and talk tests were rather accurate for their initial group of (mostly elite) clients but as their business expanded and their client base widened the correlation between breathing and AeT broke down.

Participant
pshyvers on #31437

Remember that knowing your exact AeT is not really all that important. If you can develop an idea that it is (for example) between 155-160bpm, that’s good enough for defining your Z1 training range.

The question for me is, what happens if we find out, months later, that we were too high or low? Wouldn’t that kind of overtraining have effects much more insidious than a single 3-hour bout? If we were undertraining, the harm would be less. But we might be sacrificing potential gains.

As I understand it, there’s nothing wrong with your estimate being a little low. There’s no particular value in training right at AeT. Your objective in Z1 training is to accumulate time somewhere in Z1, not time right at AeT.

Participant
depeyster on #31496

@pshybers Yes, I agree that false precision is a fool’s errand. Let’s take your five-point tolerance and double it.

So, the question is, what to use (parenthetical page citations from TftUA):

1. 164 plus or minus 5 from the Gas exchange test (85, 155) crossover point. This is clearly way too high for me.
2. 152 +/- 5, from my HR drift test, where I went from 152 to 156.
3. 145 +/- 5, from the Gas exchange test (85, 90, 155) point of maximum fat oxidation (fatmax).
4. 134 +/- 5, from the Gas exchange test conservatively using the FASTER study (62, fig. 2.10) RER range of 0.73-0.74.
5. ??? +/-5 using 3-4 hour time to exhaustion thought experiment. To paraphrase Scott and Steve (155-6), unlike 1-4, this is straightforward, it involves a maximum sustained effort for 3-4 hours’ duration.

Right now, I am using 130 +/- 5 bpm, on the principle that you succinctly stated that it is better to be a little undertrained than overtrained.

But the values of AeT candidates range from 134 to 164. I don’t think that anyone would argue that narrowing that range is a demand for false precision.

Inactive
Anonymous on #31602

A multi-hour threshold test isn’t practical nor useful. How likely are you to do it more than once?

Thresholds are not innate, unchanging performance benchmarks. They’re in flux. It’s much better to use a shorter test that’s a proxy for real performance that you can do repeatedly and track your progress. That’s why we use the drift test.

Participant
depeyster on #31691

That makes great sense. Thanks Scott!

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