Tissue traction theory: caused by muscle injury. Muscle spasm theory: caused by repetitive muscle cramps. Connective tissue theory: Injury to the connective tissue of the muscle (e.g., tendon). In fact, chronic muscle soreness is the result of a splitting muscle injury. Ways to avoid muscle soreness: 1. Muscle stretching exercises (performed in a static manner) 2, the principle of increasing the load: muscle training overload principle makes the muscles are prone to injury, with the principle of increasing the load, slowly improve the quality and quantity of muscle training, in order to effectively avoid the occurrence of injury. 3, appropriate supplementation of vitamin C, but still need further analysis to confirm. Delayed onset muscle soreness refers to the phenomenon of muscle soreness that occurs only a few hours to about 24 hours after exercise, and usually lasts for one to three days or so. Delayed muscle soreness is caused by muscle injury, muscle spasm or connective tissue abnormalities, but it is generally believed that connective tissue abnormalities are the biggest cause of delayed muscle soreness. The general public’s notion that muscle soreness is caused by lactic acid buildup is incorrect. The best way to prevent muscle soreness is to perform muscle activities in a gradual manner so that the muscles can be loaded with the heavy or repeated exercises that will be performed. If muscle soreness is already present, rest and heat therapy should be used to treat it, and over-activity is not advisable, otherwise more serious injuries are likely to occur. It is a chronic and repeated accumulation of microscopic injuries. It often occurs in areas where there is excessive muscle activity or persistent muscle tension in static positions. It can be divided into two categories: acute and chronic. The common areas are the muscles of the back, neck and legs.