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Previous theories of muscle fatigue assumed that lactic acid was the primary cause of limiting endurance exercise performance. Lactic acid was considered a waste product of anaerobic metabolism and a cause of muscle fatigue during high-intensity exercise.
It directly leads to metabolic acidosis during exercise, resulting in reduced muscle contraction and cessation of exercise. Lactic acid is thought to cause delayed onset muscle soreness (DOMS). However, many studies have refuted these previous arguments. This article will clarify the most common misconceptions about 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 converted into pyruvate to produce ATP. Pyruvate is oxidized and metabolized to yield more ATP in the presence of oxygen, but in the absence of oxygen it is metabolized to lactic acid.
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Incorporate the benefits of lactic acid to the human body
Some scientists believe that lactate can be viewed as an acidic buffering substance in the human body. Through the mechanism of production and rapid removal of 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 inhibit hyperkalemia in skeletal muscles.
In addition, the production of lactic acid has other advantages such as: B. Stimulating hemoglobin release of more oxygen, stimulating ventilation, improving muscle blood flow and increasing cardiovascular drive. Apparently, lactate may play a role in metabolic acidosis and physical fatigue.
Tongtong 2⟫Why is lactic acid produced?
In the past, we thought that lactic acid was a product of anaerobic intense physical exercise, because during intense physical exercise, the human body cannot provide sufficient oxygen concentration in time, and the accumulated pyruvate is converted into lactic acid due to the anaerobic loading state. But oxygen is just one of the reasons why lactate increases when we exercise at higher intensities. Other reasons are:
– Utilization of fast-twitch muscle fibers, oxygen delivery efficiency, muscle hypoxia, acceleration of glycolysis and capacity of mitochondrial energy metabolism
– Various factors, including the ability of other cells in the body to secrete and utilize lactic acid.
The reason that lactic acid in the blood can maintain a constant concentration (about 1 mM) at rest is because the production and excretion of lactic acid are in balance.
Point 2: Does exercise lead to lactic acid buildup?
Although lactic acid is produced by exercise, these lactic acids quickly break down into hydrogen ions, and the remainder combine with sodium ions (Na+) or potassium ions (K+) to form lactate, so there is no lactic acid in the muscles. When there is too much lactic acid, the level in the blood is lower, but it is in the form of lactate.
Regarding lactate, although oxygen uptake and utilization increases linearly with exercise intensity, lactate production does not increase linearly with exercise intensity, but rather increases steadily until exercise intensity exceeds a threshold. It rises sharply, meaning it increases significantly if the training load is too high.
Point 3⟫Is physical fatigue caused by the accumulation of lactic acid?
Because lactic acid (salt) increases with physical fatigue, many scientists previously believed that lactic acid was the cause of physical fatigue during high-intensity exercise. However, there is now a growing body of evidence that breaks the previous link 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 convert lactate into energy (ATP) under aerobic conditions.
Lactate therefore serves as an energy source for the skeletal muscles during exercise and is also available as an energy source for the heart, brain, kidneys and liver!
In addition, lactic acid, which is not oxidized in the manner described above, diffuses from the exercising muscles into the capillaries and is transported through the blood to the liver, where it is synthesized again into glucose. Therefore, the lactic acid accumulated during exercise will decrease approximately 1 to 2 hours after the end of 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) formed during anaerobic metabolism
2. Changes in the proportion of energy-rich phosphates
3. Oxidative stress metabolites such as reactive oxygen species (ROS)
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Point 4⟫Is muscle soreness caused by the accumulation of lactic acid?
In fact, the phenomenon of delayed onset muscle soreness 1 to 3 days after training is not significantly related to the formation of lactic acid. This type of delayed-onset muscle soreness often occurs when training volume and intensity increase suddenly and rapidly and there is a strong eccentric muscle contraction. The following conditions are the main causes of delayed onset muscle soreness.
1. Causes slight rupture of muscle fibers.
2. Ultrastructural muscle damage
3. Sensitized nocireceptors
The concentration of lactic acid in the blood depends on its ability to produce and excrete it. Through training, the human body can achieve greater buffering and tolerance to lactate accumulation, so that less lactic acid is produced under the same load, and athletes can produce less lactic acid even during intense physical exercise. A large amount of lactic acid is produced, thereby training the body’s ability , to excrete this lactic acid, thereby increasing the lactic acid threshold and strengthening the athlete’s anaerobic ability!
Diploma”
Lactate is more of a friend than an enemy to athletes. In sports research, the lactate concentration in the blood is also used as an indicator for measuring the endurance of athletes and is used to assess the anaerobic metabolism of athletes and to monitor the physiological exercise intensity.
Text/Nutritionist Zeng Yijun
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