What Is Lactate? Definition, Function, and Role in Sports Performance

The Function of Lactate in the Body and Exercise Metabolism

Lactate has long been studied in sports physiology and is routinely measured, especially in endurance athletes. In the late 1970s, the term “lactate threshold” was coined by sports scientist Alois Mader. He conducted the first fundamental research to establish the lactate threshold at an average of 4 mmol lactate per liter of blood. He also applied the threshold concept to define training zones based on it.

Why Lactate Is Important for Energy and Muscle Function

For a long time, lactate was considered a metabolic waste product that accumulates in the muscles during intense physical activity and leads to fatigue. However, recent findings have shown that lactate is not a waste product and is not the primary cause of physical exhaustion. In fact, lactate has been shown to have many important functions in metabolism—particularly as an energy source for muscles and the heart, as well as in cell signaling.

How Is Lactate Produced in the Body?

Lactate is produced in cells during a process called glycolysis. When carbohydrates are broken down, lactate is formed. This is then converted to acetyl-CoA, which enters the citric acid cycle for further aerobic (oxygen-based) metabolism and forms ATP (adenosine triphosphate). ATP is the energy required for muscle contraction.

Lactate vs. Lactic Acid: Common Misunderstandings Explained

Lactate is often mistakenly referred to as lactic acid, and its association with acid is frequently misunderstood as a cause of fatigue and muscle pain. However, this is not entirely accurate. In fact, the lactate molecule itself cannot be directly converted into an acidic compound. The reason lactate is associated with acidity lies in the following biochemical process: Lactate is actively transported out of the cell via a protein carrier called the MCT (monocarboxylate transporter). This carrier binds lactate and transports it across the cell membrane along with hydrogen ions (H⁺). These hydrogen ions are responsible for lowering the pH and contributing to the increased acid load.

Lactate as a Key Product in Muscle Metabolism

Recent studies show that significantly more lactate than pyruvate is formed during glycolysis, and that lactate is the main product used in further metabolism via the citric acid cycle. During physical exertion, most of the lactate is produced in the working muscles, where the turnover of ATP and energy for muscle contraction is high.

Anaerobic Metabolism and Rising Blood Lactate Levels

During very intense exertion—such as short sprints—with correspondingly high energy demands, the lactate is transported directly out of the cell after glycolysis and is not further metabolized in the citric acid cycle. The measurable lactate level in the blood rises sharply. This is referred to as anaerobic metabolism (without oxygen), which produces significantly less energy overall in the form of ATP.

Lactate and Fat Metabolism in Endurance Athletes

Compared to carbohydrate metabolism, beta-oxidation (fat breakdown) produces acetyl-CoA, which also enters the citric acid cycle and leads to ATP production.
This is typically the reason why athletes with a very high fat metabolism capacity have lower lactate levels.
In addition to muscles, lactate is also an important substrate for the liver. The liver is a crucial organ for regulating blood sugar levels. A drop in blood sugar can lead to a drop in performance—something many people refer to as “hunger fever” or “hitting the wall.” Athletes and coaches can use devices such as the Lactate Scout Sport to test threshold levels and define training zones more precisely.

Lactate as an Energy Source for the Liver and Blood Sugar Regulation

Lactate serves as an energy source for the liver and is used to produce new glucose in a process called gluconeogenesis. This is an efficient way to maintain blood sugar levels during physical exertion.

Ready to test lactate in the field? Discover the Lactate Scout Sport — our handheld lactate analyzer designed for athletes, coaches, and sports science professionals.

If you’re in Germany, you can buy the Lactate Scout Sport and accessories from our German web shop: lactatescout.shop