During expiration, does the diaphragm contract or relax?

During expiration, the diaphragm relaxes. This relaxation of the diaphragm is a crucial component of the respiratory cycle. Inhalation occurs when the diaphragm contracts and moves downward, increasing the thoracic cavity volume and allowing air to flow into the lungs. Conversely, during expiration, the diaphragm returns to its dome-like shape, which decreases the volume of the thoracic cavity, facilitating the expulsion of air from the lungs.

Additionally, when the diaphragm relaxes, the elastic recoil of the lungs plays a significant role in pushing air out. This process is primarily a passive one during normal expiration, meaning that it does not require active muscle contraction but rather utilizes the natural elasticity of lung tissue. Understanding this cycle is essential for recognizing how respiratory mechanics function, particularly during different phases of breathing.