What type of breathing occurs without muscular effort?

The correct answer is passive breathing, which is the type of breathing that occurs without muscular effort. This process primarily relies on the natural elasticity of the lungs and the thoracic cavity. During passive breathing, inhalation occurs through the expansion of the chest and diaphragm due to atmospheric pressure, while exhalation takes place as the lungs and chest wall recoil.

Passive breathing is common during rest or sleep when the body does not require additional air exchange beyond basic oxygen intake and carbon dioxide removal. By contrast, forced breathing, active breathing, and controlled breathing involve an increased effort where the respiratory muscles are actively engaged to meet higher demands for oxygen, such as during exercise or stress. Therefore, recognizing the distinction between these different types of breathing is crucial for understanding respiratory physiology and the body's reaction to various conditions.