"The AT, also known as the lactate threshold, is the point where lactate (lactic acid) begins to accumulate in the bloodstream."

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Lactate Threshold is the point at which lactate rises 1 mmol above the baseline level. This would be about 2.0 to 2.5 mmol in most people, and does not necessarily mean that it is "accumulating", which implies an inexorable increase. LT is not measured by heart rate. It can only be measured with blood testing. There are other definitions of lactate that measure degrees of accumulation or steady-state levels of lactate ("MLSS" and "OBLA" for example).

LT is often approximated by using a HR/ventilation test, and is termed "AT". But, AT is not LT.

As the other poster noted, they are intended to be the same thing, but they are not, and they are easily dissociated from one another.

Another note: LT is measured as lactate level plotted against power (biking) or pace (cycling), and so would reference not a HR level, but a power level or running pace. Again, in the absence of a power or pace measuring device, it's common to use HR as a proxy for these more accurate and precise measurements.

I know this is nitpicky but isn't this...

"LT is often approximated by using a HR/ventilation test, and is termed 'AT'."

...usually referred to as "ventilatory threshold" which is only an approximation of LT. In common useage (including one medical textbook on respiratory medicine, AT and LT are used interchangeably.

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To make things more confusing, the very first measurable rise in plasma lactate (eg 1mmol above baseline) is often being called "aerobic threshold" whereas the point where lactate levels start to rise exponentially being "anaerobic/lactate threshold".



On a related note not that I'm looking at this stuff, Juilan what do you think of this article?

http://www.ncbi.nlm.nih.gov/...55&dopt=Abstract

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Yes, the original work in defining "AT" was as a ventilatory measurement. That's precisely why they're not precisely the same. And yes, LT and AT are commonly interchanged, but are not the same, depending on context and the precision required from the context.

A given athlete might get the same power data point at LT and AT. But, then have that athlete repeat the tests pedaling at 110 rpms (versus say 85 in the original tests). That athlete's AT power will now be lower (or, HR higher at given power) than LT power. The two measurements behave differently under different conditions.

My point exactly! While I think the authors used the term "aerobic threshold" in place of the more widely preferred "lactate threshold", their findings show that LT- and HR-based intensity measurements are closely related, despite being different things.

Power at a given lactate level went up as the subjects got more fit. HR stayed the same (statistically) as the subjects got more fit. HR is a practical marker of training intensity under normal conditions.

This why, despite its drawbacks, HR zone training works. I don't think it works as well as power-based training, but it does work if used properly.

What the study doesn't explore (at least not in the abstract) is how HR and LT effort measurements might have diverged in training. The biggest pitfall to HR training is that people think that those zone caps are like the word of God and can never be violated. We have to push past them to get more fit.

One other note: This study used direct lactate measurements to determine "HR at LT". This is not the same method as used in determining a true ventilatory "AT" heart rate; for the usual AT test, one would measure power while observing HR and breathing directly (eg, a Conconi test).

OK, I take it back. Here's what I was thinking of:

www.triathlonacademy.com/articles/ LymanAerobicThresholdTest.pdf



Didn't some of these figures also appear in Triathlete or some other magazine? The first figure show AeT before the 1mmol rise in lactate. But LT (where the lactate curve rises exponentially) is clearly higher than 1mmol over baseline. The more I look into it, the more variability in definitions of AT/LT etc. I find.

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So if one wanted to train at LT over period of weeks or months, wouldn't the best training guide be HR (or PRE) not power, as power at LT will change as fitness develops? I think we agree that HR is a fine tool for guide training. I'm just not understanding why, if you believe the results of that study, you think power is better.

An example: Athlete X does at Computrainer test with blood lacatate sampling and it's determined that LT was reached at 200W as well as a HR of 170bpm. 2 months later, if he wants to do an LT workout, 200W may be too easy as his fitness has improved, but hitting a HR of 170 will keep him at LT.

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Beats me. The only thing that makes sense to me is that LT/AT/whatever you want to call it should be defined when the slope of lactate curve changes. 1 mmol over baseline seems a little arbitrary to me. What do you think?

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First, let's re-emphasize that when saying "LT" we really mean "power output at LT". So, if you train at that power level all the time, what happens? Not much, actually. You plateau after a short while and stagnate.

Ok, so what if you instead train at the HR that corresponds to LT all the time? Perhaps the power at that HR will trend upwards. But, perhaps not. You will likely still get stuck. I sure did when I tried it.

I think the most efficient (in use-of-time-terms) way to raise the power produced at LT is to train at above-LT power levels. If LT power is, say, 175, then doing 20-40 minute efforts at about 220 watts would lift LT power most effectively. Complement one or two of these per week with endurance rides 10-15% below LT and you've got yourself a nice training program. Power at the HR that corresponds to LT will rise.

If you're using HR as a guide instead of power/pace, you'll do these workouts at the HR that corresponds roughly to the middle miles of a 10K, or to the late stages of a half marathon. In any event, HR remains merely a marker for the true physiological work effort and training effect. It's the power we produce that induces adaptations, not our HR. HR just tags along for the ride.

Well, this discussion is clearing things right up.

Can someone contrast and compare LT to AT? What's the diff? What's the import of the diff to training?

Does anyone have a link to an article in a reputable journal?

It's not arbitrary, in the sense that one must choose something that can be replicated and means ("marks") basically the same metabolic activities across many subjects. We can't do science without definitions, and the LT definition (used properly) has proved a good one.

Good points everyone. LT and AT have been improperly interchanged in training circles, articles, and scientific literature to the point now that everyone is confused. I think they've been pretty well defined here, and if someone could sift out some good compare / contrast for the group that would be great.

But I just wanted to add a point about using HR for LT training- it will change too. HR "zones" are variable as well and as fitness improves, the athletes I coach will inevitably come to me and say, "I did the threshold intervals today again, great workout but I just couldn't get my heart rate up there." No, these athletes are not overtrained, but because their blood volume, stroke volume, and nervous system had been stimulated to improved performance, the HR zones need to be adjusted down.

So my point is, whether you train by HR, LT, AT, Power, Pace, whatever, the target you are trying to hit at "threshold" is constantly moving so frequent testing or adjustment of zones is important. That's why formula based zones never work.

Clear as mud, eh? ;-)

Lactate Threshold -- A direct, invasive measurement of actual blood lactate concentrations. Involves taking blood and analyzing it periodically during an increasing power test. The classic definition is the power level at which the concentration first moves above "baseline" by 1 mmol. Some texts use a pegged number of 2.5 mmol ("milli-mole") instead. As long as the same definition is used across trials in any given study or application, it seems to make no material difference to the validity of the study. Regardless of what you might read in Tri magazines or on Mark Allen's website, LT can only be precisely measured with blood testing.

LT is best stated as a power level (or pace for runners): "My LT is 175 watts", "My LT is 7:00 per mile," etc.

In real life, LT power is roughly a maxed-out 3 to 3.5 hour effort on a bike. Frankly, LT power is lower than most coaches and training gurus would have you believe. Fit half IM athletes can sit on LT for the bike. In an IM, most everybody has to sit below LT; elites will exceed it for stretches.

Aerobic Threshold -- Another testing method (first researched intensively in Germany, I think), wherein the observer does not take blood, but rather takes HR and breathing measurements. In the classic application, at some point as the power is raised, HR goes from rising steadily to rising faster or even exponentially. That "inflection point" is defined as AT. AT will sometimes correspond to LT, but not always. Due to its imprecision, it is virtually never used in a serious study.

In real life, people define AT all over the place. I personally like Gordo Byrn's method of simply becoming aware of your breathing; when you first begin to breathe more deeply, that's about the low end of your AT (which he calls "AeT" to be more clear in his writings).

One other acronym: Anaerobic Threshold. Well, this is the messy one, because there simply is no consistent definition or way of measuring it. Again, contrary to what Tri magazine articles and Mark Allen say, the aerobic system doesn't magically "switch over" to the anaerobic system at some point. Both are working, in varying proportions, all the time. There is no threshold that is crossed.

I once worked out with a wise coach who shrugged when I asked about Anaerobic Threshold. He just said, "It's that effort level where you know you'd better slow down right away or your day is over." A physiologist might say this is somewhere near VO2max, or Maximal Aerobic Power -- but I think that, in general, Anaerobic Threshold is a messy and pointless concept for the vast majority of our training efforts. But, since its acronym is "AT", it gets confused with the other "AT".

As for the difference to your training -- not a lot. To find your benchmark for a long, steady effort, read Gordo Byrn's "Four Pillars" articles on his website. That's what he calls AeT; it is inherently close to LT (although a bit lower, IMO). Use that HR range as your anchor point for a mix of workouts below, at and above AeT.

This stuff is perhaps best found in a textbook, rather than a journal article. But, I don't know of a good textbook reference.

If you believe that study, by staying at the HR that corresponds to LT, RPE will stay about the same but power will increase as you become more fit. Clearly that was not your experience, but that's the logic that follows from the study. Now of course like almost all these sports studies it was small and (I don't think) independently verified, so it could all be BS... I don't know.

I don't claim to know the best way to raise LT power - but you hear all the time though that it's good to train right at or just above LT effort. Seems like your method calls for intervals at about 125% of LT power which seems a little higher than "just above" LT (however one defines that) but hey, if it works that's all that matters.

Out of curiosity, what distances do you do?

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YES!

And this is why I think that there should be a migration to a power-duration (or pace-duration) method of defining training zones. Instead of measuring the "indicators" of training effort, we can instead directly measure the effort via pace and power.

Instead of benchmarking to indicators such HR or lactate, we benchmark to a chosen spot on the power-duration curve. As long as the duration axis is 20 minutes or longer, it doesn't much matter which one we choose, since they all stay relatively linked as fitness waxes and wanes. In cycling, the consensus has already built around the 60-minute mark, since it's nearabouts to a 40k TT time, and one's periodic benchmark test doubles as a good intensity workout. With the "Power at 60 Minutes" benchmark in hand, we can set our training intensities relative to that number, and those intensities shift up and down naturally with our fitness. An endurance ride is 60-75% of 60-minute power; a tempo ride is 76-90% of 60-minute power; etc. Heart rate be damned -- it's the work rate that counts.

For running, I think Daniels wrote the book on pace-duration training (literally) in Daniels' Running Formula. Benchmark yourself to your 10k or half mary time, and pick your training paces relative to that pace.

Under the power-duration or pace-duration paradigm, the HR monitor becomes an interesting thing on your wrist, but no longer dominates your training life. And -- we can happily forget all about this LT and AT and AeT stuff...

Thank you. That was EXACTLY what I wanted to know.

No, no. The study was a snapshot in time, before and after a training cycle. During the training cycle we can be sure those athletes trained at well above LT power levels and RPE levels from time to time. That's how they raised their power in the first place. Don't confuse the study as saying that the "path from here to there is at LT" -- it merely says that, after fitness improved, HR & RPE at LT power stayed roughly the same. It says nothing about a training protocol.

My training focus these days is on Oly and Half IM distance, with a long-range plan to do IM next year. My long ride is 4 hours, and long run is 2.5 hours. 13-15 hours a week total, with zero swimming this year.

ANAEROBIC THRESHOLD. (Braunwald: Heart Disease: A Textbook of Cardiovascular Medicine, 6th ed.)

[/url]Anaerobic threshold is a theoretical point during dynamic exercise when muscle tissue switches over to anaerobic metabolism as an additional energy source. All tissues do not shift simultaneously, and there is a brief interval during which exercise muscle tissue shifts from predominantly aerobic to anaerobic metabolism.[9] [12] [17] [19] Lactic acid begins to accumulate when a healthy untrained subject reaches about 50 to 60 percent of the maximal capacity for aerobic metabolism. The increase in lactic acid becomes greater as exercise becomes more intense, resulting in metabolic acidosis. As lactate is formed, it is buffered in the serum by the bicarbonate system, resulting in increased carbon dioxide excretion, which causes reflex hyperventilation. The gas exchange anaerobic threshold is the point at which Eincreases disproportionately relative to O2 and work; it occurs at 40 to 60 percent of O2 max in normal, untrained individuals.[9] Below the anaerobic threshold, carbon dioxide production is proportional to oxygen consumption. Above the anaerobic threshold, carbon dioxide is produced in excess of oxygen consumption. There are several methods to determine anaerobic threshold, which include (1) the V-slope method, the point at which the rate of increase in CO2 relative to O2 increases (see Fig. 6–1) ; (2) the point at which the O2 and CO2 slopes intersect; and (3) the point at which the ratio of VE/O2 and end-tidal oxygen tension begins to increase systematically without an immediate increase in the VE/O2 (see Fig. 6–1) . The anaerobic threshold is a useful parameter because work below this level encompasses most activities of daily living. Anaerobic threshold is often reduced in patients with significant cardiovascular disease. An increase in anaerobic threshold with training can enhance an individual's capacity to perform sustained submaximal activities, with consequent improvement in quality of life and daily living. Changes in anaerobic threshold and peak O2 with repeat testing can be used to assess disease progression, response to medical therapy, and improvement in cardiovascular fitness with training.

Lactate Threshold

Murray & Nadel: Textbook of Respiratory Medicine, 3rd ed., [/url]

As early as 1807, Berzelius recognized the presence of lactic acid in muscle, believing its concentration to be proportional to the prior level of exertion.[63] Fletcher and Hopkins[64] subsequently provided the definitive evidence that lactic acid is a normal physiologic consequence of metabolism rather than an artifact of the preparation. It was not until 1927 and 1930, however, that Douglas[56] and Owles[65] demonstrated that a range of work rates could be performed in humans that would result in no discernible increase of blood lactate concentration. More recently, it has been widely confirmed that the arterial blood lactate concentration begins to increase at a highly reproducible O2 (for a specific task) and continues to increase the higher the work rate up to the limit of tolerance. This O2 was called by Wasserman and McIlroy[19] the anaerobic threshold.

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Yes, of course there are published definitions. If you look farther into the library stacks, you'll find that they diverge. Some replicate other definitions (LT, VO2max, etc.), others break new ground. The definition you found occurs at nearly the exact point of LT as defined above. It's the gas-exchange version of finding that first inflection point, and is even more cumbersome to do in real life than blood-lactate testing or HR testing.

Not that the definition you provide is wrong. It's just that I don't think it informs us the way that simpler and more widely accepted benchmarks do.

None of this matters if we follow a power-duration paradigm instead. After all, it's sort of hard to do a 4-hour training ride dragging a metabolic cart around with us and breathing through a tube. ;-)

Maybe that's a good idea! Or at least be clear what you mean when one says LT or AT. There's a big difference between the 2.5mmol lactate/~3hr effort LT and the 1hr-TT effort (does this correspond to ~4.0mmol lactate number I see sometimes?) LT, but people use the term to mean both. As a short course triathlete the latter number is more useful for me.

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