Which muscle is considered the chief muscle of inspiration?

The thoracic diaphragm is considered the chief muscle of inspiration because it plays a crucial role in the respiratory process. When the diaphragm contracts, it flattens and moves downward, which increases the volume of the thoracic cavity. This expansion creates a negative pressure that draws air into the lungs. This function is vital during inhalation, providing the primary force that allows air to flow into the respiratory system.

While the external intercostals assist during inspiration by elevating the ribs and expanding the chest cavity, they are not the primary muscle responsible for this action. The rectus abdominis, on the other hand, primarily functions in forced expiration rather than inspiration, and the internal intercostals mainly assist in expiration as well. Hence, the thoracic diaphragm's unique anatomical position and its ability to significantly alter thoracic volume make it the chief muscle driving the process of inhalation.