2024-01-30 04:49:17
Past muscle fatigue theories believed that lactic acid was the main culprit that limited endurance exercise performance. Lactic acid was considered to be a waste product of anaerobic metabolism and the cause of muscle fatigue during high-intensity exercise.
It will directly lead to metabolic acidosis during exercise, resulting in reduced muscle contraction and cessation of exercise. It is believed that lactic acid causes delayed muscle soreness (DOMS). However, many studies have overturned these past arguments. This article will break down the common misunderstandings regarding lactic acid one by one.
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Key point 1⟫What is lactic acid?
ATP is an immediate source of energy for skeletal muscle contraction during exercise. During exercise, glycogen and glucose can be metabolized into pyruvate to produce ATP. Pyruvate is oxidized and metabolized to obtain more ATP in the presence of oxygen, but it is metabolized into lactic acid in the absence of oxygen.
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Integrate the usefulness of lactic acid to the human body
Some scholars believe that lactate can be regarded as an acidic buffer substance in the human body. Through the mechanism of producing and quickly removing lactate, it can delay the occurrence of acidosis in the human body. Studies have also shown that an acidic environment has a protective effect and can Inhibits hyperkalemia in skeletal muscle.
In addition, the production of lactic acid has other benefits, such as: prompting hemoglobin to release more oxygen, stimulating ventilation, enhancing muscle blood flow, and increasing cardiovascular drive. Clearly, lactate may play a role in metabolic acidosis and exercise fatigue.
Tongtong 2⟫Why lactic acid is produced?
In the past, we thought that lactic acid was a product of anaerobic intense exercise, because the human body cannot provide sufficient concentration of oxygen in time during high-intensity exercise, and the accumulated pyruvate is metabolized into lactic acid due to being in an anaerobic state. But oxygen is only one of the reasons why lactate increases when we exercise at a higher intensity. Other reasons include:
– Usage of fast-twitch muscle fibers, oxygen delivery efficiency, muscle hypoxia, acceleration of glycolysis, and mitochondrial energy metabolism capacity
– Various factors including the ability of other cells in the body to clear and utilize lactic acid.
The reason why lactic acid in the blood can maintain a constant concentration (regarding 1 mM) during rest is that the production and elimination of lactic acid are balanced.
Point 2: Will exercise cause lactic acid accumulation?
Although exercise will produce lactic acid, these lactic acids will quickly dissociate into hydrogen ions, and the remaining ones will combine with sodium ions (Na+) or potassium ions (K+) to form lactate, so there will be no lactic acid in the muscles. If there is too much Lactic acid, the content in the blood will be less, but it will exist in the form of lactate.
In terms of lactate, although the absorption and utilization of oxygen increases linearly with exercise intensity, the production of lactate does not increase linearly with exercise intensity, but increases steadily until the exercise intensity exceeds a threshold. It increases sharply, so it does increase significantly when the exercise load is too high.
Point 3⟫Is exercise fatigue caused by lactic acid accumulation?
Since lactic acid (salt) increases with exercise fatigue, many scholars used to believe that lactic acid was the cause of exercise fatigue during high-intensity exercise. However, there is now more and more evidence that overturns the past correlation between lactic acid and exercise fatigue.
Because lactate is recycled by the body, the heart, brain, and slow-twitch fibers can remove lactate from the blood very easily, so if the lactate produced by the fast-twitch fibers is transported to the slow-twitch fibers or another area that is not yet metabolically overloaded, These muscles can convert lactate back into pyruvate and metabolize lactate into energy (ATP) under aerobic conditions.
Lactate therefore serves as a fuel source for skeletal muscles during exercise and is also a fuel source available to the heart, brain, kidneys and liver!
In addition, lactic acid that is not oxidized in the above way will diffuse from the exercising muscles into the capillaries and be transported to the liver through the blood to be re-synthesized into glucose. Therefore, the lactic acid accumulated during exercise will decrease approximately 1 to 2 hours following stopping exercise. It will return to the resting state.
What really causes fatigue are the following three reasons:
1. Increase in intermediate products such as phosphate (Pi) produced during anaerobic metabolism
2. Changes in the proportion of high energy phosphates
3. Metabolites with oxidative stress such as reactive oxygen species (ROS)
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Point 4⟫Is exercise soreness caused by lactic acid accumulation?
In fact, the phenomenon of delayed onset muscle soreness 1 to 3 days following exercise is not significantly related to the formation of lactic acid. This type of delayed-onset muscle soreness often occurs when a sudden and rapid increase in exercise volume and intensity, and a large amount of eccentric muscle contraction, occur. The following conditions are the main causes of delayed-onset muscle soreness.
1. Cause minor breakage of muscle fibers.
2. Ultrastructural muscle damage
3. Sensitized nocireceptors
The concentration of lactic acid in the blood comes from the production and elimination ability. Training can make the human body have greater buffering and tolerance for lactate accumulation, so that less lactic acid is produced under the same load, and athletes can also Under intense exercise, a large amount of lactic acid is produced, training the body’s ability to eliminate this lactic acid, thereby increasing the lactic acid threshold and strengthening the athlete’s anaerobic ability!
Conclusion⟫
Lactate is a friend rather than an enemy of athletes. In sports research, blood lactate concentration is also used as an indicator to measure athletes’ endurance, and is used to evaluate athletes’ anaerobic metabolism and monitor physiological load intensity.
Text/Nutritionist Zeng Yijun
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