What occurs when the chest muscles relax during exhalation?

When the chest muscles relax during exhalation, the process of breathing out occurs. This relaxation allows the thoracic cavity to decrease in volume, leading to an increase in pressure within the chest cavity compared to the outside atmosphere. As a result, air is pushed out of the lungs. This is a key aspect of the mechanics of breathing known as passive exhalation, where the elastic recoil of the lungs and associated structures helps to expel air efficiently when the muscles, including the diaphragm and chest muscles, are no longer actively contracting.

This physiological response is crucial for maintaining proper gas exchange in the lungs, ensuring that carbon dioxide is expelled and fresh oxygen is brought in during inhalation.