During exercise, which muscle primarily increases airflow?

• A. Pectorals
• B. External intercostals
• C. Sternocleomastoids
• D. Diaphragm

Answer: (C)

The main idea is that airflow during breathing is driven most by the diaphragm. When the diaphragm contracts, it moves downward, increasing the vertical dimension of the thoracic cavity and lowering the pressure inside the chest. This pressure drop pulls air into the lungs, making the diaphragm the primary muscle that increases airflow.

External intercostals assist by lifting the rib cage to enlarge the chest further, which is especially helpful as ventilation needs rise during exercise. In very intense breathing, accessory muscles like the sternocleidomastoids can help lift the sternum and clavicles to expand the upper chest even more, and muscles such as the pectoralis major can aid when the arms are fixed, but these play a supporting role. So, the diaphragm is the main driver of the increased airflow.