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Lactate Threshold 1 (LT1): A Comprehensive Guide to Boosting Endurance Training.

Lactate threshold 1 (LT1), also referred to as the aerobic threshold, is the sibling of LT2, which is known as the anaerobic threshold. While LT2 receives more focus, LT1 plays a crucial role in renowned training methods for cycling, running, and triathlon, such as Polarized training, Pyramidal training, and the Norwegian Method. This article provides a comprehensive understanding of the initial lactate threshold.


LT1 (Lactate Threshold 1) refers to the exercise intensity at which there is a noticeable increase in blood lactate concentration compared to when the body is at rest. This should not be confused with LT2 (Lactate Threshold 2), also known as the anaerobic threshold and max lactate steady state.


Determining the precise intensity at which lactate increases can be challenging, especially without continuous blood lactate monitoring. As a result, LT1 is often identified as the point where blood lactate concentration reaches 2 mmol/l.


During rest, lactate concentration is low but not zero, indicating a small amount of lactate production and clearance.


At very low exercise intensities, the aerobic energy system becomes more active and helps burn lactate. Consequently, lactate concentrations are lower during a cycling warm-up compared to when the body is at rest.


As exercise intensity increases, the glycolytic energy system also becomes more active, causing lactate production. Eventually, lactate concentrations reach a point where the first lactate threshold (LT1) is achieved.


It's worth noting that LT1 is referred to as a threshold, despite not causing any dramatic changes when exercising slightly above it. Lactate concentrations tend to stabilise at this point.


How to Determine LT1?


To accurately determine LT1, you need to take blood lactate measurements at different exercise intensities.


There are two ways to measure LT1: in a controlled lab setting using equipment like a cycling trainer, running treadmill, or rowing ergometer, or during a field test by running on a track or repeatedly cycling up a hill.


By plotting your lactate measurements on a graph, you can create a lactate curve that will indicate your LT1 (refer to the image below). However, there are three important points to consider:

1. The intensity of LT1 can be influenced by the test protocol. Longer interval steps may lead to lower lactate concentrations at lower intensities, affecting the point at which the lactate concentration reaches 2 mmol/l. Additionally, less trained athletes may exhibit an immediate increase in lactate, making the starting intensity of the protocol crucial in determining LT1.


2. The measured lactate concentration is influenced by various factors, including exercise intensity, body composition, and measurement errors. Ignoring these factors may yield inaccurate results. For more reliable analysis, consider using the INSCYD performance software, which accounts for these variables and generates a lactate curve based on your data.


3. While the theoretical definition of LT1 is clear, determining LT1 in practice can be challenging. Studies have shown that visually identifying LT1 can lead to significant discrepancies between observers. To ensure consistency, it is recommended to standardise the LT1 determination process.

Lactate Threshold 1 (LT1) vs Lactate Threshold 2 (LT2): Understanding the Differences


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 endurance training, LT1 represents the point at which lactate concentration begins to rise compared to resting levels. It is important not to confuse LT1 with 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 the aerobic threshold, occurs at a lower exercise intensity than LT2, or the anaerobic threshold. While LT2 is shown on the graph, it is not derived from it.


Unlike LT2, where lactate concentrations rise over time above the threshold and remain steady below the threshold, there is no clearly visible difference between below and above LT1.


Lactate Thresholds and Training Zones


Lactate Threshold 1 (LT1) and Lactate Threshold 2 (LT2) are commonly used to establish a 3-zone training model:

- Training zone 1: below LT1

- Training zone 2: between LT1 and LT2

- Training zone 3: above LT2


However, this model has limitations. For example, if you want to train at FatMax, it is difficult to determine whether to aim for zone 1 or zone 2. It is much simpler to use the INSCYD training zones, which precisely indicate the intensity at which maximal fat combustion occurs.


Another drawback is that these zones are too broad. Zone 3 encompasses a wide range of intensities, from approximately a 1-hour time trial to a 5-second sprint. On the other hand, zone 1 can be too easy, requiring runners to walk, and causing swimmers to struggle with maintaining proper form.


In contrast to the 3-zone training model, the INSCYD training zone builder helps create customised training zones that align with individual needs.


Understanding the difference between LT1 and LT2 is crucial in any sports training program. It determines whether lactate concentrations remain steady or continuously rise. However, a deeper understanding is necessary to create an effective, personalised training regimen.


If you aim to train at FatMax, how do you determine the optimal fuel requirement for exercising in zone 1? The traditional 3-zone model leaves many questions unanswered and untapped opportunities.

This is where INSCYD comes in. Our advanced training zone builder enables you to accurately assess the amount of carbohydrates you burn at different exercise intensities and training zones. It allows for the creation of training zones tailored to your specific needs, from maximising fat combustion to the intensity of a 5-second sprint.


Say goodbye to guesswork and one-size-fits-all approaches. With INSCYD, you gain access to a precise, scientifically-backed training methodology tailored to your athletes' unique physiology.


Should You Want to Increase LT1?


We have learned that LT1 does not signify a significant change in physiological processes; therefore, it cannot be considered a true threshold. Additionally, relying on LT1 alone does not help in creating valuable training zones.


So, why would you want to increase LT1?


Some coaches argue that increasing LT1 indicates an improvement in the performance of the aerobic energy system or fat combustion. However, instead of focusing on increasing the indicator itself, it makes more sense to directly target the end goal, such as enhancing the aerobic energy system or fat combustion.


INSCYD allows you to measure and improve what truly matters, rather than relying on indicators that are a combination of several factors. Here are two potential goals that can indirectly increase LT1:


How to Increase Lactate Threshold 1 (LT1)?


1. Decrease Lactate Production and Carbohydrate Combustion:

- Reduce your anaerobic energy supply, which will result in a decrease in lactate production and carbohydrate combustion. This, in turn, will lead to an increase in LT1. You can find practical tips on this topic in the article "5 Training Tips to Decrease VLamax," applicable to running, cycling, swimming, and other endurance sports.


2. Increase Lactate Combustion and Fat Combustion:

- Boost your aerobic energy contribution to enhance lactate and fat combustion, consequently increasing LT1. There are various methods to achieve this, ranging from long slow distance endurance training to high-intensity VO2max intervals. Learn more about these strategies through the provided link.


Aerobic Threshold, Ventilatory Threshold, and FatMax


In this final part, we will discuss metrics often associated with the first lactate threshold.


LT1 vs. Aerobic Threshold:

The first lactate threshold (LT1) is often linked to the aerobic threshold (AeT), and some even use these terms interchangeably. Whether LT1 and the aerobic threshold are truly the same depends on the definitions used.


Although both LT1 and the aerobic threshold indicate an increase in anaerobic energy contribution, it is important to note that this occurs even at rest. Neither LT1 nor the aerobic threshold represent a shift from fully aerobic to fully anaerobic energy supply, the start of carbohydrate combustion, or a transition from 100% fat combustion to 100% carbohydrate combustion. Additionally, they do not reflect a limited availability of oxygen. In steady-state conditions, both aerobic and anaerobic energy contributions are present.


LT1 vs. Ventilatory Threshold 1 (VT1):

Another metric often associated with LT1 is the ventilatory threshold 1 (VT1). Unlike LT1, which is determined by lactate samples, VT1 is measured using a metabolic cart (VO2 analyser). VT1 represents the intensity at which ventilation increases at a faster rate than oxygen consumption.


While LT1 and VT1 are measured differently, some studies suggest that they correspond to similar exercise intensities. However, both LT1 and VT1 are challenging to pinpoint due to the lack of clear definitions and detection methods.


LT1 vs. FatMax:

Many cyclists, runners, and coaches mistakenly believe that LT1 corresponds to FatMax, the peak intensity at which fat combustion occurs. They often use LT1 and FatMax interchangeably, particularly when determining the zone 2 training intensity proposed by Iñigo San Milan.



Although both LT1 and FatMax occur at intensities below the anaerobic threshold, they do not necessarily coincide at the exact exercise intensity. Increasing the aerobic energy contribution can raise both LT1 and FatMax, creating a correlation between the two. However, for questions regarding fuelling for training sessions below LT1 or determining energy expenditure (fat and carbohydrates) at or below LT1,

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