Lactate threshold 1 (LT1) – also known as the aerobic threshold – is the little brother of LT2 or anaerobic threshold. LT1 may not get as much attention as LT2, but it’s still a key ingredient of famous cycling, running, and triathlon training methods. This includes Polarized training, Pyramidal training and the Norwegian Method. This article covers everything you need to know about the first lactate threshold.

Two cyclists in endurance training with overlay of Lactate Threshold 1 (LT1) graph.
Image: INSCYD partner Pro Cycling – Movistar Team

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There are several LT1 definitions, but this is probably the most common.

LT1 is the lowest exercise intensity at which there is a measurable increase in blood lactate concentration, compared to resting lactate concentrations. LT1 is the first lactate threshold and should not be confused with LT2 (lactate threshold 2, or anaerobic threshold).

In practice, it’s not always easy to determine the lowest intensity at which there is a measurable increase in lactate. This is especially true when you don’t measure blood lactate continuously. Therefore, LT1 is also often defined as the intensity at which blood lactate concentration equals 2 mmol/l.

When you’re at rest, your lactate concentration is low. However, it’s not zero. This means that there is a small lactate production and a small lactate combustion (clearance).

When you start to exercise at a (very) low intensity, your aerobic energy system becomes more active. This aerobic energy system combusts lactate. As a result, lactate concentrations are lower at low exercise intensities. For example, lactate levels will be lower  during a cycling warm up – compared to lactate concentrations at rest.

When you increase the intensity a bit further, your glycolytic energy system becomes more active too. This anaerobic energy system produces lactate. As a result, lactate concentrations will rise at some point. This is the first lactate threshold, LT1.

It’s important to note that although LT1 is called the first lactate threshold, you could argue whether it is actually a threshold. Nothing dramatic happens when you exercise slightly above LT1; lactate concentrations remain in steady state.

An LT1 test requires blood lactate measurements at several exercise intensities. Here’s how to take valid blood lactate samples: Free E-course: the complete guide to taking valid lactate samples.

You can measure LT1 in a lab setting, for example on a cycling trainer, running treadmill or rowing ergometer. You can also measure LT1 in a field test when running on a track or repeatedly cycling up a hill.

By fitting a curve through your lactate measurements, you’ll get a lactate curve (see image below). This curve shows your LT1. However, there are 3 things to keep in mind:

  1. The intensity of LT1 is highly determined by the test protocol. Longer steps can result in lower lactate concentrations at low intensities, which affects the intensity at which the lactate concentration reaches 2 mmol/l. Moreover, less trained athletes can show an increase in lactate straight from the start, which means LT1 is directly determined by the starting intensity of the protocol. 
  2. The lactate concentration that you measure depends on several other factors, such as: exercise intensity, body composition, measurement errors. If you don’t take these into account, you can get flawed results. The INSCYD performance software takes all these factors into account and creates a lactate curve from your data.
  3. Although the theoretical definition of LT1 is clear, determining LT1 turns out to be challenging in practice. Literature shows that a visual detection of LT1 leads to relevant differences between observers. That’s why it is suggested to standardise the determination of LT1

The theoretical definition of LT1 is clear, but in practice it can become challenging to determine LT1 based on a lactate curve. Here are example lactate curves. Where do you mark the LT1 intensity? Literature suggests to standardise the method of determining LT1. INSCYD does so for you, by defining LT1 as the intensity at which blood lactate concentration is 2 mmol/l.

As a sports coach or human performance lab expert, you understand the critical role lactate threshold plays in determining endurance performance.

INSCYD performance software takes the complexity out of performance analysis, providing clear and reliable data to guide your training plans. This is your chance to be at the forefront of sports science!

Don’t miss the opportunity to enhance your training methods and outcomes. Schedule a free call with one of our INSCYD experts today to learn more about how our cutting-edge technology can elevate your performance training.

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Lactate Threshold 1 (LT1), also known as the aerobic threshold, occurs at a lower exercise intensity than Lactate Threshold 2 (LT2), or the anaerobic threshold.

In the context of endurance training, LT1 is marked as the first rise in lactate concentration compared to resting lactate concentrations. This should not be confused with the second lactate threshold, LT2, which occurs at higher exercise intensities.

LT1 is called the first lactate threshold, because it occurs at lower intensities than LT2, the second lactate threshold.

LT1 (or aerobic threshold) occurs at a lower exercise intensity than LT2 (or anaerobic threshold). LT2 is marked in this graph, but not derived from this graph.

As mentioned earlier, LT1 is not really a threshold. Nothing dramatically changes when you exercise slightly above LT1: lactate concentrations will remain in steady state. LT2 on the other hand is a “threshold” because it clearly differentiates two intensities from each other: 

  1. Above LT2, lactate concentrations will rise over time. There is no more lactate steady state.
  2. Below LT2, lactate concentrations will not increase over time. There is a lactate steady state.

With LT1, there is no such clearly visible difference between below- and above LT1.

Lactate Threshold 1 (LT1) and Lactate Threshold 2 (LT2) are often used to create a 3 zone training model:

  • Training zone 1: below LT1
  • Training zone 2: between LT1 and LT2
  • Training zone 3: above LT2

However, you’ll soon notice that creating zones like this only allows for limited possibilities.

For instance, if you want to train at FatMax, should you aim for zone 1 or zone 2? It’s much easier to simply use the INSCYD training zones, that tell you exactly at which intensity maximal fat combustion occurs.

Stryd running power training zones + fat and carbohydrate utilization

One of many examples of training zones created with the INSCYD training zone builder. In this running example, fat and carb combustion is added to the training zones.

Another aspect is that the zones are too large. Zone 3 is everything from a ~1 hour time trial intensity to a 5 second sprint. On the other side of the spectrum, zone 1 can be so easy, that runners need to walk and swimmers struggle to remain horizontal.

Contrary to the 3 zone training model, the INSCYD training zone builder helps to create training zones that exactly fit your needs

Understanding the difference between LT1 and LT2 is key in any sports training regimen. It’s the difference between lactate steady state and a continuous rise in lactate concentration. Yet, it’s not enough to create an effective, individualized training program.

What if you want to train at FatMax? How do you know how much fuel you need when exercising in zone 1? The traditional 3-zone model leaves many questions unanswered and opportunities untapped.

This is where INSCYD comes into play. Our sophisticated training zone builder enables you to see how much carbohydrates you burn at every exercise intensity and in every training zone. It helps to create training zones that fit your needs exactly, from maximal fat combustion to the intensity of a 5-second sprint.

No more guesswork, no more one-size-fits-all. With INSCYD, you get a precise, scientifically-backed approach to training that is tailored to your athlete’s unique physiology.

Don’t settle for less when you can optimize your training with INSCYD. Book a free consultation with one of our experts today in your own language and let us show you how we can elevate your athlete’s training.

Be part of the future of sports training. With INSCYD, you have the power to redefine what’s possible.

We learned that LT1 does not mark a significant change in physiological processes, hence it’s not really a threshold. We also learned that LT1 doesn’t help when creating valuable training zones.

So why would you want to increase LT1?

Some coaches will say: because an increase in LT1 is an indicator of an increase in the performance of the aerobic energy system. Or maybe an indicator of an increase in fat combustion. But why would you aim to increase the indicator, when you can also directly aim to increase the end goal? In this case: aerobic energy system or fat combustion.

INSCYD allows you to measure and improve what matters, instead of focusing on indicators that are a combination of several factors. Here are two possible goals you could have that have the side effect of increasing LT1.

If your goal is to decrease lactate production and/or carbohydrate combustion at any given exercise intensity, you should decrease your anaerobic energy supply. This will also result in an increase of LT1. Here are 5 practical tips on how to do that: 5 Training tips to decrease VLamax. You can implement these tips in running, cycling, swimming and all other (endurance) sports.

If your goal is to increase lactate combustion (clearance) and fat combustion at any given exercise intensity, you should increase your aerobic energy contribution. This will also result in an increase of LT1. There are several ways to do this. They range from “long slow distance” endurance training to high intensity VO2max intervals. Learn more about this topic via this link.

In this last part of the article, we look at metrics that are often associated with the first lactate threshold.

The first lactate threshold is often associated with the aerobic threshold (AeT). Some even use these terms interchangeably.

You could say that LT1 describes a way to measure the aerobic threshold, namely with lactate measurements.

Whether LT1 and the aerobic threshold are the same depends on the definitions you use.

Both LT1 and the aerobic threshold mark a point at which anaerobic (glycolytic) energy contribution shows a measurable increase. Note though that (as always during an incremental test) the aerobic energy contribution is still dominant.

Common misunderstandings about both LT1 and aerobic threshold:

  • They don’t mark the start of anaerobic energy contribution. As we mentioned, even at rest there’s an anaerobic energy contribution.
  • They don’t mark a shift from fully aerobic to fully anaerobic energy supply.
  • They also don’t mark the start of carbohydrate combustion. Even at rest, carbohydrates are burned.
  • They don’t mark a shift from 100% fat combustion to 100% carbohydrate combustion.
  • They don’t mark a limited oxygen availability.
Energy contribution percentage aerobic and anaerobic

In steady state conditions, there’s always a combination of aerobic AND anaerobic energy contribution.

Another metric often associated with LT1 is the ventilatory threshold 1 (VT1).

Contrary to LT1, the ventilatory threshold 1 is measured with a metabolic cart (VO2 analyzer) instead of with lactate samples. VT1 is the intensity at which ventilation starts to increase at a faster rate than oxygen consumption.

Similar to LT1, you could say that VT1 is a way to measure the aerobic threshold. Although their measurement techniques are different, it will not surprise you that some studies show that LT1 and VT1 mark similar exercise intensities.

There is another similarity: the intensity at which ventilation starts to increase at a faster rate than oxygen consumption (VT1) is at least as hard to spot as the lowest intensity at which there is a measurable increase in lactate (LT1). Therefore, VT1 is also not clearly defined nor easy to detect.

LT1 vs FatMax

Lastly, many cyclists, runners and their coaches think LT1 is the intensity at which fat combustion peaks (FatMax).

It is true that both LT1 and FatMax occur at an intensity below the anaerobic threshold. It is also true that you can increase LT1 and FatMax by increasing the aerobic energy contribution, all other things equal. As a result, you will find a correlation between LT1 and FatMax. However, they don’t necessarily occur at the same exercise intensity.

Moreover, if you want to answer questions like: “How to fuel for a training session at or below LT1?” or “How much energy, fat and carbohydrates do I burn at or below LT1?”, you still need more information besides an LT1 or FatMax intensity.

To answer these questions, simply use the INSCYD fat and carbohydrate combustion graph, combined with the LT1 exercise intensity.

Fat & carbohydrate combustion graph

The fat and carbohydrate combustion graph shows exactly how much energy you burn at a given exercise intensity, like at or below LT1.

Understanding and effectively increasing your LT1 can be a game-changer in your athletic performance. Navigating these complexities on your own, however, can prove to be challenging.

Luckily, we have an exciting solution coming soon! INSCYD College – educational platform is designed to transform athletes into champions and assist businesses in their growth. It will offer comprehensive and actionable courses tailored for coaches and athletes at different levels, providing expert-led education.

In addition to the rich educational content, the platform will even offer opportunities for certification and Continuing Education Units (CEUs). If you’re interested in taking your understanding of LT1 and other performance metrics to the next level, INSCYD College could be your key.

Wrap up and next step

LT1 – also known as the aerobic threshold – is the first lactate threshold. It marks a measurable increase in lactate concentration compared to rest.

We learned that:

  • LT1 does not mark a significant change in physiological processes, hence it’s not really a threshold.
  • LT1 is not a good way to determine training zones or substrate (fat vs carbohydrates) utilisation.
  • LT1 is an indicator for performance changes, but it makes more sense to focus on the actual end goal (e.g. increasing the performance of your aerobic energy system) instead.

Now it’s time to learn more about training zones that work much better than LT1 based training zones. 

You’ve uncovered the science behind LT1. But understanding the theory is just one part of the equation. Practical application requires expert guidance, state-of-the-art tools, and personalized strategies. This is where we come in.

At INSCYD, we’ve turned complex sports science into actionable insights for coaches and human performance labs worldwide. Our cutting-edge performance software takes into account a multitude of factors that significantly affect your athlete’s overall performance.

Schedule a free 1:1 call with an INSCYD expert today and start the journey towards mastering your athlete’s performance and beyond. Learn how to integrate our scientifically backed tools into your training plans, or how to offer more precise performance assessments in your lab.


A visual detection of LT1 leads to relevant differences between observers:
Faude, O., Kindermann, W., & Meyer, T. (2009). Lactate threshold concepts: how valid are they?. Sports medicine (Auckland, N.Z.), 39(6), 469–490. [LINK]

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