During the inhalation in the lungs, the pressure in the lungs is lower than atmospheric, while during the exhalation, the pressure is higher. As a result, the process allows air to move into the lungs from the atmosphere and back. However, lungs cannot move by themselves. Normal quiet breath is associated with the activity of the diaphragm and the external intercostal muscles. As a result, during the inhalation, the diaphragm goes down, the ribs rise, and the distance between them increases. This process increases the volume of lungs, decreasing the pressure and allowing air to move inside the lungs. The process is similar to ventilators, where the movements of pistons pump the air by increasing and decreasing air pressure.