• Introduction
  • Basics of lactate
  • How does the body get rid of lactate?
  • Difference between lactic acid and lactate
  • Final thoughts
  • Sources
  • Aerobic respiration: producing energy (ATP) with the presence of oxygen.
  • Anaerobic respiration: producing energy (ATP) without the presence of oxygen.
  • Cori Cycle: a metabolic pathway in which lactate is transported to the liver, converted to glucose, and transported back to the muscles, where it is metabolized back to lactate.
  • Gluconeogenesis: synthesis of glucose from nonsugar precursors (lactate, pyruvate, etc.). 
  • Lactate: a byproduct of anaerobic respiration which can be used to generate more ATP.
  • Lactic acidosis: lactic acid production exceeds lactic acid clearance.
  • Maximum oxygen uptake: The maximum amount of oxygen a person can use during intense exercise.

Introduction

Energy metabolism consists of complex interconnected pathways that break down nutrients to form adenosine triphosphate (ATP). These processes can be divided into three separate systems; aerobic respiration, anaerobic respiration, and the phosphagen system. 

ATP itself is known as the energy currency in your body. It is used to maintain regular bodily functions like breathing, heartbeat, hormonal activity, cell repair, etc. During rest and low-intensity exercise, most of the ATP produced aerobically. As the intensity of the exercise grows, your body is no longer able to deliver enough oxygen to the working muscles. Instead, your muscles turn to anaerobic respiration to generate ATP at a faster rate. This process also creates a byproduct that is thought to cause fatigue – lactate. 

This post breaks down what lactate is, how it is formed, and what effects it has on your performance. 

Basics of lactate

In both aerobic and anaerobic metabolism, your body breaks down glucose into a byproduct called pyruvate through a complex series of steps. When your cardiorespiratory system (heart, lungs, veins) is able to deliver enough oxygen to meet the body’s oxygen demand, pyruvate is sent to your muscle cells’ mitochondria (powerhouse of the cell). There, pyruvate is processed into more energy.

When oxygen is limited, pyruvate is turned into lactate, allowing glucose breakdown and energy production to continue. This process also releases a hydrogen ion (H+) within the muscle fibers. Contrary to popular belief, it is the hydrogen ions (along with inorganic phosphates from the breakdown of creatine phosphate) that create acidic conditions within the muscle. This stimulates the muscle’s pain receptors resulting in a familiar “burning” sensation during intense exercise.

To prevent lactic acidosis (dangerous levels of acidity), your body has built-in mechanisms to keep muscle pH at a manageable level. For example, to protect cells from excessive acidity, lactate and hydrogen ions exit the cells into the bloodstream to be delivered elsewhere. Additionally, the same metabolic pathways that break down glucose into ATP perform poorly in an acidic environment. Thus, your body simply cannot sustain a high intensity to a point where it becomes dangerous.

Although lactate is often seen as an unwanted byproduct of anaerobic respiration, it plays an important role in cellular processes that generate more ATP. It is no longer seen as a culprit of muscle fatigue, but an important fuel for many cells. In fact, certain tissues such as the heart and slow-twitch muscle fibers can use lactate as a direct source of fuel.

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Lactate

A byproduct of glycolysisAn important intermediate in energy metabolismCan be directly used as fuel by muscles, kidney, liver & heartHydrogen ions (H+) lower muscle's pH and cause a burning sensationTraining reduces lactate accumulation & buffering

How does the body get rid of lactate?

Lactate is removed in three main ways; oxidation (50-80%), gluconeogenesis (10-25%), and transamination (5-10%).

In well-oxygenated cells, it can be converted back into pyruvate and undergo oxidative phosphorylation. This produces vast amounts of energy. Oxidation is by far the predominant process of lactate clearance both during and after exercise.

Instead of accumulating in the muscles, excess lactate can also be transported to the liver. There, it is first converted into pyruvate and finally back to glucose in a process called gluconeogenesis. The newly-formed glucose is then transported back to working muscles via the bloodstream. This entire process is called the Cori Cycle.

Lastly, lactate can be turned into amino acids and keto acids in a process called transamination. Both of which can be further broken down to generate more ATP

Difference between lactic acid and lactate

Lactic acid and lactate are often used interchangeably. Although they refer to the same phenomenon, they are technically different.

An acid is a substance that can donate a hydrogen ion (H+). One example of this is lactic acid. When lactic acid donates a hydrogen ion, it becomes its conjugate base – lactate. 

In the human body, most of the lactate dissociates quickly, meaning that it exists in the form of lactate – not lactic acid.

The soreness you experience during intense exercise is caused by hydrogen ions in the blood.

Final thoughts

Lactate is often described as an athlete’s worst enemy. However, it is quite the opposite – it is an important mechanism that regulates the breakdown of fat and sugar for energy. With consistent training, you can also increase your lactate threshold, and your ability to perform in high-lactate conditions. 

To reduce the negative effects of lactate in your performance, you can perform continuous endurance training at a moderate pace or focus on high-intensity interval training. The first one improves your aerobic capacity (VO₂max), especially the function of your mitochondria. Thus, allowing you to better utilize oxygen for energy production. The latter specifically focuses on performing at a high intensity for an extended amount of time.

Did you learn anything new about lactate? Let us know in the comments. 

Sources

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  • Lund, J., Aas, V., Tingstad, R.H. et al. Utilization of lactic acid in human myotubes and interplay with glucose and fatty acid metabolism. Sci Rep 8, 9814 (2018). https://doi.org/10.1038/s41598-018-28249-5
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