What type of breathing is characterized by the involvement of external intercostal muscles?

The involvement of external intercostal muscles is primarily associated with resting inhalation. During this phase of breathing, a person is at rest, and inhalation is typically a controlled and active process. The external intercostal muscles contract to elevate the ribs and expand the chest cavity. This expansion decreases the pressure within the thoracic cavity relative to the atmospheric pressure, allowing air to flow into the lungs.

This mechanism is essential for efficient gas exchange, as it increases lung volume and therefore allows for a greater intake of air. In contrast, the other options involve different processes: forced expiration typically requires the use of abdominal muscles for maximum expiration; active exhalation involves muscle contractions rather than the passive return of the diaphragm and intercostal muscles to their original positions; and passive respiration predominantly relies on the natural elasticity of the lung tissue without additional muscle involvement during exhalation. Understanding the role of the external intercostal muscles during resting inhalation helps clarify the mechanics of normal, effortless breathing.