There are eight abdominal muscles. The chest is two pectoral muscles that are exercised from top to bottom, namely the lateral, middle and medial. Generally speaking, the medial muscles are the most difficult to train. The medial muscle is rarely used in daily life, and it is divided into 4 upper abdomen and 4 lower abdomen. The upper abdomen is relatively easy to practice, and you can practice sit-ups lying flat. The next four pieces are more difficult to practice, and you need to do leg lifts. You must stick to them.