What is the active, muscular part of breathing called?

The active, muscular part of breathing is known as inhalation. During inhalation, the diaphragm and intercostal muscles contract, causing the thoracic cavity to expand. This expansion reduces the pressure within the lungs compared to atmospheric pressure, allowing air to flow in. It is during this phase that oxygen is brought into the lungs, which is essential for gas exchange.

In contrast, exhalation and expiration refer to the process of expelling air from the lungs, which is primarily passive and relies on the relaxation of the diaphragm and intercostal muscles rather than muscular effort. Inspiration, while it may seem synonymous with inhalation, is often used in a broader context that can include both inhalation and the entire breathing process. Therefore, the term inhalation is most accurate when describing the specific active phase of breathing that involves muscle contraction.