AT vs LT (What's the difference?)

[trischnitz]

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.

[Ashburn]

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?

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.

[jhc]

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.

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?

[Ashburn]

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.

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…

**

[Cyborg42]

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

[Ashburn]

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.

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.

[jhc]

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

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., **

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 Hopkins64] 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 Douglas56] and Owles65] 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 McIlroy19] the *anaerobic threshold. *

[Ashburn]

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

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.

[jhc]

we can happily forget all about this LT and AT and AeT stuff…

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.

[Flying_Wombat]

Good explanation.

According to McArdle, Katch and Katch, Essentials of Exercise Physiology

"the term anaerobic threshold originally defined the abrupt increase in ventilatory equivilent caused by non metabolic carbon dioxide production owing to lactate buffering. Some researchers believed this point signaled the body’s shift to anaerobic metabolism (lactate formation) and therefore proposed the anaerobic threshold as a non-invasive measure of the the onset of anaerobiosis. **Subsequent research **shown that the ratios of VE/VO2 or VCO2/VO2 do not necessarily link in a *causal *manner with lactate production or accumulation in exercise. Even if the association between ventilatory dynamics and cellular metabolic evens in noncausal, useful information about exercise performance can be obtained by applying these indirect proceedures"

Sounds like there is a quasi relationship between the two, AT relates to gas exchange (increase in CO2 production), LT relates to the increase in blood lactate. Both require testing equipment not available to most of us. I agree with previous posters that power or pace are better indicators, after all, that is what a race measures.

[Flying_Wombat]

whoops!

should have said “cellular and metabolic events is non causal”

[Ashburn]

…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.

I think the 4 mmol level is near to the 1-hour TT effort, but I’m not certain.

And, I think that the 60-minute TT power benchmark is useful to all athletes at all distances. A short course athlete might spend proportionately more time at the higher percentages of that power, and IM folks would spend more time under it. But, the benchmark is relevant – and very important – to both.

True “LT power” explains (“predicts”) upwards of 90% of the variation in power output of *any given longer effort *across different athletes. By extrapolation, so too would 60-minute power. The power-duration paradigm is useful and valid for all endurance athletes, regardless of specialty.

[jaylew]

Ok, after reading this, I am completely confused. I thought that anaerobic threshold and lactate threshold were basically the same thing and that the AT that Gordo describes is aerobic threshold which is significantly lower than lactate threshold. I’ve been working under the assumption that my lactate threshold and aerobic threshold are about 25-30 beats different.

I’m confused how they could be the same number when one is the so called “first opening of breath” and the other a number I can’t reach unless going very hard.

What Aet is Gordo talking about? Aerobic threshold, anaerobic threshold or ananerobic threshold? I’m completely lost now.

[Ashburn]

What Aet is Gordo talking about? Aerobic threshold, anaerobic threshold or ananerobic threshold? I’m completely lost now.

At the risk of soundling glib – Gordo is talking about what Gordo is talking about. It’s not right or wrong. The point is that he defines a benchmark.

His favored benchmark is easy to find, easy to refer to, and is consistent “enough” for an athlete over the course of a season. It is “accurate without being precise.”

Gordo uses a ventilatory reference point for determining the following basic effort measure:

“OK! Now I’m working. This is where I start getting a training benefit.”

He has his crew work at certain levels above and below that point to get various training benefits. It’s the same as with all the other reference point training systems. This basic effort measure is at the core of all these various things. “When am I beginning to do some meaningful work?”

None of these reference systems are ideal. All involve some compromise.

LT (lactate test) is troublesome, because we can’t run around pricking our fingers; Anaerobic Threshold (as defined in the textbook excerpt above) is troublesome because we don’t own metabolic carts. The “original” Aerobic Threshold is pretty good since we can buy HR monitors cheap, and do a Conconi test on a Computrainer or treadmill, or even at the track.

Gordo’s “AeT” is very good because anybody can wear a HR monitor and go out and run and become self-aware. Some would argue it’s not precise enough, since HR varies so much. I think power/pace is the most precise, but you’ve gotta buy a Powertap or the like, and a pace meter like a Timex or Garmin GPS.

In sum: They’re all just ways of attempting to measure just how hard we are working. We can measure all these various “markers”:

Thing Measured – Common Paradigm Name

HR – Aerobic Threshold

Breathing Rate – Gordo’s AeT

Lactate – Lactate Threshold

Gas Exchange – Anaerobic Threshold

Power and Pace – Power/Pace Duration Curve

They all work, if used properly. I like Gordo’s AeT and the Power/Pace Duration systems the best.

[JustCurious]

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?

Defining LT as a 1 mmol/L increase over baseline is arbitrary, but has been used by some because it is less subjective than trying to determine exactly where the slope changes. Only a handful of people actually use this definition, though.

To answer my own question re. Hellerman: a PubMed search reveals three papers, two original articles and one that appears to be a review in a clinical journal.

To complicate things even more, blood lactate clearance/buffering/usage is also not a constant. It also increases with exercise intensity, though not to the same extent and with a bit of a time lag.

Find that workload where blood lactate takes off non- linearly and hold that intensity and the curve will flatten again and blood lactate will tend to level out at some elevated level.

I’m convinced that due to these inaccuracies and day to day variability, complex metabolic testing is probably only of real value to scientists. For coaches and athletes, simple field tests are more than adequate. Seems that scientists not only can’t agree how to define ‘lactate threshold’, many say that the term is a misnomer. In real life, the pace or power output you can maintain for 30 minutes or an hour or whatever is what’s really important, no matter what name you give it.

[jhc]

The “original” Aerobic Threshold is pretty good since we can buy HR monitors cheap, and do a Conconi test on a Computrainer or treadmill, or even at the track.

I think the Conconi test is used to estimate anaerobic threshold, not aerobic threshold.

Otherwise great list.

[smartasscoach]

Everytime a simple question like freestyle’s pops up in a group like this, a discussion like this always ensues.

The people with a physiology background start discussing the definitions of the metabolic thresholds and the heart of the question is lost. And that’s where exercise physiology departs from the real world of training… the same real world that they were supposed to study and help.

Even though all these discussions are very enlightening, the real world fact is that lactate testing works in the real world. Most people that say that this or that method of calculating the lactate threshold doesn’t work, is not accurate, etc, has never done any testing, only read the papers. The Conconi test? Yep, also works. Time-trials, races run as tests? Yep, they’re the best in fact!

For the coaches and athletes out there, the question is: How can I measure the intensity of the exercise I am performing in a practical and cost-effective way? And in order to do that, several practical tools are available that work.

The cost-effective part is also something important. Cost-effective doesn’t mean cheap. It means the best method of controlling intensity for the level of the athlete. It kind of bothers me when some coaches try to sell power training on the bike for age-group athletes, even real good ones. Or lactate testing. It’s simply a way to make a(nother) buck out of the sport.

Paulo

[jhc]

“Everytime a simple question like freestyle’s pops up in a group like this, a discussion like this always ensues.”

Hey, it’s a lifestyle forum right?

Now how do you feel about gay marriage?

[smartasscoach]

I’m all for it, sad marriages are not that fun… (lame joke, I know)

Now those newbies really need to learn to ride before racing!

[jhc]

Now those newbies really need to learn to ride before racing!

Especially those with clincher “race” wheels…