What is the definition of active expiration?

Active expiration is defined as a process that requires muscle effort to expel air from the lungs, typically during vigorous breathing or physical exertion. This process predominantly involves the contraction of the abdominal muscles and the internal intercostal muscles. These muscle contractions create increased pressure within the thoracic cavity, pushing air out of the lungs more effectively than passive mechanisms, which rely primarily on the elastic recoil of the lungs.

The understanding of this concept is essential in exercise physiology, as recognizing when active expiration occurs helps in maintaining proper respiratory mechanics during different intensities of physical activity and can influence how breath control is managed during exercises or athletic performance.

In contrast, quiet breathing, characterized in one of the other options, largely relies on passive expiration, where the diaphragm and external intercostal muscles relax, allowing the elastic recoil of the lungs to push air out without additional muscular effort. The other options refer to processes that do not specifically describe active expiration, further reinforcing why the correct definition focuses on the involvement of muscles during forced exhalation.