1) Why warm up? In order to ensure safety, we usually need to do a warm-up exercise before exercise. It has two advantages: 1. It can improve the body temperature of the main parts of the body. (2) Stretching exercises that allow more blood (oxygen) to flow to muscles to prepare the body for more intense activity will make tendons more flexible, because it increases body temperature and increases the range of motion of joints, thereby avoiding joint, ligament and muscle damage. A) Which muscles need to be preheated? Warm-up exercises should focus on large muscle groups. Practitioners can warm up by walking in situ, twisting waist, raising knee, etc. If chest and shoulder, they can turn around, raise arms and circle, etc. People who like to run or jump rope can start with a 3-5 minute brisk walk and some stretching exercises. B) It takes about 3-5 minutes to warm up before the body realizes how much blood it needs to deliver to the muscles. Warm-up exercises should last for about 5-10 minutes and should be accompanied by stretching exercises of major muscle groups.