During exercise, the muscle uses glucose and oxygen for energy. Glucose comes from the blood or is formed from glycogen stored in the muscles. Oxygen is supplied with the blood stream. During muscular work, glucose is oxidized by oxygen, turning into energy. But oxygen is almost always not enough for full oxidation. Therefore, lactic acid accumulates in the muscles. It causes a feeling of heaviness and pain in the muscles, gives us a feeling of fatigue. Therefore, aerobic exercise – associated with breathing, for example, running, skiing, is more useful for muscles.
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