Muscle soreness after exercise is mainly caused by the accumulation of lactic acid in the muscle tissue, which can cause pain due to nerve irritation. Because lactic acid is an acidic substance that is normally broken down by blood sugar into carbon dioxide and water when it is used for energy supply, excessive muscle exercise can cause a lack of timely oxygen supply, and then energy needs to be supplied quickly, so it can lead to the formation of lactic acid when the product is not fully oxidized. Lactic acid is actually an acid that stimulates pain receptors and causes pain. But lactic acid can continue to be broken down into energy, so muscle pain will disappear after a few days.