We get tired when we work hard, lift weights, run, exercise. Most of the muscles in our body get tired, but have you ever wondered why your heart, which has been beating before you were born and has been beating all your life, never gets tired? It is estimated that at the age of 80, your heart beats approximately 3,363,840,000 times. But still the muscles of the heart (cardiac_muscle, from which the heart is made) do not get tired, while the muscles that make us move, and which we can control at will, that is, our skeletal_muscles get tired.
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Like living cells, muscle cells also need energy to function. The energy of the cells is in the form of ATP. The cell uses most of the glucose to make its own energy (ATP). We call it cellular_respiration. If a cell uses oxygen to make energy from glucose, this process is called aerobic_respiration, and for that aerobic respiration the blood carries oxygen to the cells. If the cell does not use oxygen for energy, it is called anerobic_respiration. In aerobic respiration the cell gets more ATPs (calculated 36) while in anerobic respiration only 2 ATPs are found. At the same time, a chemical called lactic_acid is formed during anerobic respiration. To make energy, the cell has an organelle called mitochondria for this process.
When you work hard on your skeletal muscles, the energy needs of those muscles increase, but the blood is not able to give oxygen to the cells of these muscles so fast, and then these cells start making energy without oxygen. That start anaerobic respiration, which results in the formation of lactic acid which accumulates in the muscles, and
It causes fatigue in lactic acid.
To eliminate this lactic acid, this lactic acid travels through the bloodstream to the liver, where it is converted back into glucose. (cori_cycle).
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It is a common misconception that peels in muscles are also caused by lactic acid. In fact, the most common cause of stress (DOMS) is small cracks in the muscles, which are caused by strenuous exercise.
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The reasons why cardiac muscles do not get tired are:
- Heart muscles have a higher number of mitochondria, heart muscles have about 35% more mitochondria than skeletal muscles. Which makes more energy and does not have more anerobic respiration.
The heart gets a good supply of blood, which gives more oxygen and more aerobic respiration.
Any anerobic respiration in the heart muscle, and lactic acid, is converted back into pyruvate (the chemical that made lactic acid).
These muscles have isoenzymes for this purpose.
Heart muscles do not usually suffer from DOMS, as they do not have the same weight stress as skeletal muscles.
DOMS (Delayed-onset muscle soreness)
Exercising hard causes small cracks in the skeletal muscle fiber, then there is pain due to inflammation. Which lasts 24 to 72 hours.
