During expiration in exercise, which muscle contracts to pull the ribs down?

• A. Abdominals
• B. Internal intercostals
• C. External intercostals
• D. Diaphragm

Answer: (B)

During expiration in exercise, expiration can be active, with muscles actively pulling air out. The internal intercostal muscles pull the ribs downward and inward when they contract, reducing the thoracic volume and increasing intrathoracic pressure to push air out. The diaphragm primarily handles inspiration and relaxes during expiration, while the external intercostals lift the ribs during inspiration. Abdominal muscles can assist in forced expiration by increasing intra-abdominal pressure, but the direct action of pulling the ribs down is performed by the internal intercostals.