Lactate in Endurance Sports
Lactate or lactic acid is a product of anaerobic glycolysis. It serves a number of vital functions in the body and is an important energy source in endurance sports. The understanding and importance of lactate has steadily increased in sports science and sports medicine over the past 70 years.
Lactate Is an Energy Source
Lactate is formed as a product of glycolysis, in which the body's own glycogen reserves or carbohydrates provided exogenously are metabolized. Today, we know that lactate also has important functions beyond the supply of energy in the muscle. The lactate molecule is transported via cell-to-cell shuttles from the white, glycolytic muscle fibers to places where it is further utilized as an energy source: Besides vital organs such as the brain, heart, liver or kidneys, especially in the red, oxidative muscle fibers.
Lactate Is Always Produced
Lactate is always produced and not only after the anaerobic threshold has been exceeded, as was long assumed in sports science and sports medicine. Since the body always obtains some energy from glycolytic metabolism even at rest, lactate production and elimination always occurs. Resting lactate values are in the range of 0.5 to 1.2 mmol/l even without exercise. Lactate is highly important for the body's metabolism and function, and also supplies energy to organs and the brain.
The Importance of Lactate for Endurance Performance
Besides the benefits, lactate may well be considered an "antagonist" of endurance performance.
One reason for this is the development of lactate production during increased intensity. In contrast to the linear course of aerobic metabolism, lactate production rises exponentially with increasing intensity. At a certain intensity, lactate production then exceeds lactate clearance. The intensity at which lactate production and lactate elimination are in balance is called the anaerobic threshold. Thus, the anaerobic threshold describes a metabolic steady state and is considered an important parameter to evaluate endurance performance. If intensity exceeds the anaerobic threshold, lactate accumulates in the blood and a drop in blood-pH occurs via the co-transport of H+ ions. Therefore, one goal of endurance training is to train lactate production to be optimal for athletic demands.
Sprint test at a laboratory to measure the lactate level in the blood
Lactate production inhibits fat metabolism
During longer endurance efforts such as a cycling marathon or a long-distance triathlon, lactate does not play a very important role in the energy supply. The anaerobic metabolism and the resulting lactate determine the substrate distribution in energy production. Higher lactate production also means that fewer free fatty acids are mobilized and available for energy production in the mitochondria. Thus, lactate production inhibits fat metabolism.
How Does Lactate Transport Work?
Lactate transport takes place between cells, tissues and organs with the help of monocarboxylate transport proteins (MCT). In this process, lactate is transported from the working muscles to the heart and the oxidative muscle fibers, where it is supplied to the oxidative energy metabolism. These transport processes play an important role in the distribution of lactate as an energy source, as well as in pH regulation.
Lactate Transporter (Lactate Shuttle)
Muscle cells have two transport proteins (MCT) that are responsible for lactate transport. MCT-1 transports lactate and H+ ions into the cell and MCT-4 transports lactate out of the cell. MCTs thus determine a tissue's ability to remove H+ ions via metabolic processes and regulate pH. Oxidative muscle fibers (type 1 fibers) have more MCT-1 and fewer MCT-4 transport proteins. Thus, they take up more lactate, which is then oxidized in the mitochondria. Glycolytic muscle fibers (type 2 fibers) have more MCT-4 and fewer MCT-1 transporters, meaning they produce more lactate which is transported out of the cell than they produce.
What Does Lactate Do in the Body?
As we know today, lactate is not a waste product of metabolism, but rather an intermediate, which has many important functions. It is a link between glycolytic and oxidative metabolism. In addition to providing energy, lactate is also used to store carbohydrates, as a precursor of gluconeogenesis - the replenishment of carbohydrate stores.
Further, lactate serves as a signaling molecule for various signaling pathways. A signal transduction is a process in the body that enables it to transmit a signal from the outside into the cells. This is the only way that external stimuli induced by training can lead to physiological adaptations. Lactate serves as such a "signal" and is also considered a "lactormone" due to its hormone-like effect.
Can Lactate Increase Performance in Sports?
In short, for high-intensity efforts, such as sprinting in cycling or even short and middle distances in running, higher lactate production is important because of its functionality as an energy source. High performance also requires a lot of fast available energy. The parameter VLamax can be used to determine the contribution and maximum power of anaerobic metabolism.
Does Lactate Cause Burning in the Muscle?
The burning in the muscles is not caused by lactate. Responsible for the pain is acidosis, which is caused by a drop in blood-pH (hyperacidity), due to the H+ ions produced with higher lactate production.
What Are High Lactate Levels?
The lactate level measured in the blood is the result of constant lactate production and elimination throughout the body. When the intensity of exercise exceeds the anaerobic threshold, lactate production exceeds the body's ability to eliminate lactate. As a result, the organism can no longer maintain the steady state and lactate concentration increases.
The blood lactate concentration is the result of a multifactorial process regulated not only by the glycolysis rate in the muscles, but also by the efficiency of lactate transport by monocarboxylate transporters (MCT) between muscle cells and organs. Blood flow and nutritional status may also have an influence. Measured lactate levels in endurance sports range from 0.5 mmol/l up to over 20 mmol/l.
What Is Lactate Tolerance?
The term lactate tolerance is a bit contradictory, since lactate is an energy supplier and carrier. What matters more is how quickly the body can process lactate under the given conditions and buffer H+ ions in the blood.
Training Lactate Production and Elimination to Improve Performance
As described in this article, lactate production and transport have a major impact on our endurance performance. Consequently, it makes sense to train lactate production and clearance systematically, depending on fitness level and performance requirements.