How do internal intercostal muscles function during exhalation?

The internal intercostal muscles play a critical role in the process of exhalation by actively pulling the ribs downward and inward. When these muscles contract, they reduce the volume of the thoracic cavity, creating a pressure difference that forces air out of the lungs. This action is essential for effective breathing, especially during forced exhalation, such as during physical exertion or when speaking, which requires a more substantial expulsion of air.

Understanding their function helps clarify the mechanics of respiration, indicating that instead of simply allowing for passive airflow, the internal intercostals engage in a muscular activity that actively assists in expelling air from the lungs.