Muscle training in the gym, muscle growth outside the gym. Muscle needs full rest and excessive rest for a day or two after exercise, restore energy supply system, repair tissue damage, synthesize and thicken muscle. Therefore, in most cases, whether you feel pain or not, don't practice eating a muscle twice in a row within 24 hours. For those who have just done strength training, it is recommended not to practice too much every week, and to take a full rest for one or two days after each exercise. When the training level is improved, you can start to try more frequent training frequency, even seven times a week and twice a day. However, the principle that a muscle cannot be practiced twice in a 24-hour period remains unchanged. Then how should this contradiction be solved? This is about to mention the differentiated training method. The so-called differentiation training means that every training is not to practice all the muscles of the whole body, but only to specific muscles or muscle groups at a time. For example, the most common upper and lower limb differentiation training is to train upper limb muscles and upper arm muscles at the midpoint of the first day of training. The next day, lower limb training, focusing on hip joint training, focusing on leg and hip muscle groups. In this way, the lower limbs can rest during upper limb training, and vice versa. With the improvement of training level, it can be further differentiated. Only one large muscle group and one auxiliary small muscle group can be trained at a time, which not only has a good training effect on the target muscle group, but also can better rest the non-target muscle group. As for soreness, it is mainly caused by delayed muscle soreness.