People who don't usually exercise regularly sometimes have local muscle aches after taking part in more strenuous exercise. The reason for this phenomenon is usually considered to be related to the energy metabolism in muscles. We know that muscle contraction needs energy; Energy is provided by the decomposition of muscle glycogen in muscle tissue. In the case of adequate oxygen supply, such as muscle rest, muscle glycogen can be directly decomposed into carbon dioxide and water through pyruvate, releasing energy. However, when people are doing strenuous exercise, the decomposition of muscle glycogen is accelerated and the oxygen consumption is increased, so that the muscles are temporarily in a state of relative hypoxia. At this time, muscle glycogen can be converted into lactic acid through pyruvate and accumulated in muscle. The accumulation of lactic acid in muscle will stimulate the chemical receptors in muscle to get excited, which will spread to the cerebral cortex and make people feel sore. At the same time, due to the accumulation of lactic acid and other substances, the osmotic pressure in muscle increases, which urges muscle tissue to absorb more water, resulting in local swelling and acid swelling. Another explanation for muscle hypoxia is that when muscles are tired during exercise, slight spasm occurs due to insufficient relaxation of local muscle fibers, which makes blood vessels in muscles compressed and blood flow blocked, resulting in muscle ischemia and hypoxia. At this time, the muscles become hard and feel sore. In order to avoid or reduce muscle soreness, we should be prepared before exercise, exercise should be gradual (for example, the amount of exercise should be small at first, and then increase gradually), and after exercise, we should do some muscle relaxation activities or massage tired muscles to promote smooth blood circulation.