What happens to intercostal muscles during forced exhalation?

During forced exhalation, the internal intercostal muscles contract, pulling the ribs downward and inward to force air out of the lungs.

In more detail, the process of forced exhalation involves a more active engagement of the respiratory muscles than normal, passive exhalation. The intercostal muscles, which are located between the ribs, play a crucial role in this process. There are two types of intercostal muscles: the external intercostal muscles and the internal intercostal muscles.

During forced exhalation, it's the internal intercostal muscles that are primarily at work. These muscles are located inside the rib cage, running obliquely downward and backward from the rib above to the rib below. When these muscles contract, they pull the ribs downward and inward. This decreases the volume of the thoracic cavity, which in turn increases the pressure inside the lungs. As a result, air is forced out of the lungs and exhaled.

This process is different from normal, passive exhalation, which doesn't require the contraction of the internal intercostal muscles. Instead, during passive exhalation, the diaphragm and external intercostal muscles simply relax, allowing the lungs to recoil and air to flow out naturally.

In summary, during forced exhalation, the internal intercostal muscles actively contract to decrease the volume of the thoracic cavity and increase the pressure inside the lungs, forcing air out. This is a more active process than normal exhalation, which relies on the natural recoil of the lungs.