- inhalation - the lungs inflate with air, bringing oxygen into the body
- exhalation - the lungs let go of air, releasing carbon dioxide out into the environment
The lungs work automatically during inhalation and exhalation, expanding as breath is needed by the body, and recoiling to expel the unwanted air when it is not.
There are muscles that help to make room for the expanding and contracting lungs in the chest cavity and trunk. Because they are muscles, they work under conscious and semi-conscious control to have a major impact on the quality of the act of breathing. These are called the respiratory muscles. The respiratory muscles play a big role in body posture, as well.