Lactic acid accumulation: this is the result of long-term inactivity, and then lactic acid accumulation and muscle fiber breakage occur in muscles after exercise that day. The muscles inside are growing, and they will be there the next day. The way to get rid of it is to relax after exercise. You can take a deep breath to expel excess lactic acid from your body, or massage, soak in hot water, or heat therapy. Knead, massage, shake, etc. Generally, it won't hurt after a week. When you feel pain, you can sit down and take a deep breath to speed up the removal of lactic acid, which will also help you recover quickly. It is also helpful to practice relaxation exercise during pain.