The muscles involved in the respiratory movement are mainly the intercostal muscles, diaphragm, sternocleidomastoid muscles, abdominal muscles, etc., which function to synergize to complete the process of respiration. During inhalation, the intercostal muscles contract, the ribs move outward and upward, and the volume of the thoracic cavity increases. At this time, the diaphragm contracts downward, further enlarging the volume of the thoracic cavity, so that the air pressure in the lungs is lower than that of the outside world, and air flows into the lungs through the trachea along with the difference in air pressure until the air pressure in the lungs is equal to that of the outside world. During exhalation, which can be a natural movement when the muscles are relaxed, the diaphragm rises, the external intercostal muscles diastole will make the volume of the chest cavity smaller, and the abdominal muscles tense up to speed up the process of gas exhalation. Breathing is accomplished through the constant alternation of expiration and inhalation, constantly replacing the air in the lungs to maintain the body’s needs.