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What is Lactate Threshold, or Should We Say Thresholds?

In the world of endurance training and running, the term "Lactate Threshold" has become a cornerstone concept, but its nuances and implications are often overlooked. Unraveling the intricacies of lactate threshold reveals a fascinating interplay of physiological factors contributing to a runner’s ability to sustain effort and how to train. 

Coach Cory doing a lactate threshold run down the middle of the road

However, the traditional view of a singular lactate threshold is incorrect. This article delves into the multifaceted nature of lactate thresholds (yes, multiple lactate thresholds), exploring the primary and secondary thresholds, their significance, and the broader implications for optimizing training and performance. Welcome to a comprehensive exploration of "What is Lactate Threshold, or Should We Say Thresholds?" as we navigate the evolving landscape of endurance science.

Before discussing the lactate thresholds, we need to know what blood lactate is, its relation to running pace, and the blood lactate curve.

What is blood lactate?

In running and exercise physiology, blood lactate refers to lactate concentration in the bloodstream. Lactate is a byproduct of the body's energy production processes, particularly during periods of intense exercise. Understanding blood lactate levels is crucial for runners as it provides insights into the metabolic demands of their training and performance.

what is blood lactate

During low to moderate-intensity running, the body primarily relies on aerobic metabolism (aka the use of oxygen), where lactate production is balanced by its clearance. As running intensity increases, there comes a point where the production of lactate exceeds the body's ability to clear it, leading to a rise in blood lactate levels. This rise in blood lactate relative to running pace can be graphed to create a blood lactate curve, revealing two lactate thresholds.  Let’s dive into the lactate curve and its significance. 

What is a Lactate Curve?

A lactate curve, also known as a lactate profile or lactate threshold curve, is a graphical representation that illustrates the relationship between exercise intensity (aka running pace) and blood lactate levels. It is a tool used in exercise physiology to analyze how the body responds to increasing pace during running. 

By analyzing the lactate curve, runners and coaches can gain insights into an individual's metabolic response to exercise. Training zones, aerobic and anaerobic thresholds, and personalized workout intensities can be determined based on the information derived from the lactate curve. This helps in designing effective training programs and optimizing athletic performance.

A lactate profile graph of a untrained and well trained runner

The above picture shows a lactate curve of a new runner (turquoise) and a well-trained runner (red). The y-axis represents blood lactate levels, and the x-axis shows the running pace. Notice the difference between the two curves. Since the new runner has yet to develop their aerobic and anaerobic energy systems through training, blood lactate rises steeply. Meanwhile, since the experienced runner has spent time developing their aerobic and anaerobic energy systems through training, blood lactate increases much more slowly in a curved fashion. 

As a runner becomes more trained and the lactate curve represents a gradual curve towards the right, there are two inflection points. These inflection points on the lactate curve indicate two specific thresholds where there are notable changes in the rate of lactate accumulation. We call each inflection point the lactate threshold.

What Are The Lactate Thresholds In Running

A graph showing the two thresholds along a lactate curve

The two primary inflection points commonly identified on a lactate curve are the first lactate threshold or aerobic threshold (LT1) and the second lactate threshold (LT2), also known as the onset of blood lactate accumulation (OBLA) or anaerobic threshold. Here's an overview of each:

The First Lactate Threshold (LT1) is a critical point on the lactate curve, denoting a noticeable increase in blood lactate levels above baseline values, yet the rise remains moderate. Physiologically, LT1 signifies the stage where the body effectively clears lactate, and aerobic energy production prevails. It represents the transition from predominantly aerobic to an augmented reliance on anaerobic metabolism. LT1 is linked to a moderate exercise intensity, preceding a significant lactate level surge, making it a point where athletes can sustain prolonged efforts.

In contrast, the Second Lactate Threshold (LT2) or Onset of Blood Lactate Accumulation (OBLA) is characterized by a more rapid escalation in blood lactate levels. Functionally, LT2 marks the threshold where the rate of lactate production outpaces the body's capacity to clear lactate. This shift results in an increased dependence on anaerobic metabolism, leading to a pronounced accumulation of lactate and a swifter onset of fatigue. LT2 is associated with higher exercise intensities, typically corresponding to a pace sustainable for 50 to 70 minutes. Identifying and understanding these lactate thresholds is crucial for athletes and coaches in tailoring training regimens and optimizing performance strategies.

A graph showing how a runner goes from aerobic to anaerobic energy production

As one’s pace picks up and moves from left to right on the lactate curve, one shifts from predominantly aerobic energy to a mix of aerobic and anaerobic and, finally, primarily anaerobic. LT 1 and LT2 indicate where the predominant changes between energy systems occur. Put another way, as a runner’s pace begins to quicken, their reliance on aerobic energy decreases, and their dependence on anaerobic increases. 

What's better for distance runners, aerobic or anaerobic energy?

For distance runners, the emphasis on aerobic energy is of absolute importance, given its critical role in sustaining energy and performance over extended distances. Aerobic metabolism, dependent on oxygen availability, provides an efficient means of generating energy from carbohydrates and fats. This energy pathway allows runners to tap into substantial fuel reserves, maintaining a steady pace for prolonged durations. 

Significantly, aerobic energy production minimizes the accumulation of fatigue-inducing byproducts, such as lactic acid, contributing to a more consistent and sustained performance. The efficient utilization of oxygen in aerobic processes enhances the body's capacity to extract energy from various sources. While anaerobic energy systems may come into play during specific short races such as the 5k and faster, the bulk of a distance runner's training is dedicated to developing and optimizing aerobic capacity. 

A graph showing a lactate curve shifting to the right

The longer a runner can rely on predominantly aerobic energy, the better. Therefore, the bulk of distance runner's training should be focused on improving one's ability to sustain faster paces while using aerobic energy. This represents a shift to the right of the lactate curve.

Now, hopefully, you better understand what each lactate threshold is and the dynamic interplay between exercise intensity and physiological responses. The distinction between the First Lactate Threshold (LT1) and the Second Lactate Threshold (LT2) sheds light on the complex transition from aerobic to anaerobic metabolism, marking critical points in an athlete's capacity to sustain effort. Acknowledging these thresholds as distinct entities underscores the need for a tailored approach to training and performance optimization.

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