Human movement needs energy. If energy comes from aerobic metabolism (oxidation reaction) in cells, it is aerobic exercise. But if energy comes from anaerobic glycolysis, it is anaerobic exercise. During aerobic metabolism, fully oxidizing 1 molecule glucose can produce 38 ATP (energy unit) energy; However, in anaerobic fermentation, 1 molecule glucose only produces 2 ATP. During aerobic exercise, glucose metabolism produces water and carbon dioxide, which are easily excreted through breathing and are harmless to human body. However, a large number of intermediate metabolites such as lactic acid are produced during glycolysis, which cannot be eliminated by breathing. When these acidic products accumulate in cells and blood, they become "fatigue toxins", which will make people feel tired and weak, muscle aches, difficulty breathing, rapid heartbeat and arrhythmia. In severe cases, acidosis will occur and the burden on liver and kidney will increase. Therefore, after anaerobic exercise, people will always be exhausted, and muscle aches will last for a few days before they disappear.