Which muscles are primarily involved in the process of breathing?

• A. Abdominal muscles
• B. Diaphragm and intercostal muscles
• C. Pectoral muscles
• D. Quadriceps

Answer: (B)

Breathing relies on the chest cavity muscles that actively change its size. The main inspiratory muscles are the diaphragm, which contracts and moves downward to create more vertical space for the lungs, and the external intercostal muscles, which lift the ribs to increase the side-to-side and front-to-back dimensions of the chest. This combination allows air to flow into the lungs during quiet breathing. Expiration is usually passive as the chest returns to rest, but during forced breathing the internal intercostal muscles and the abdominal muscles help push air out by shrinking the thoracic volume and increasing intra-abdominal pressure. Among the options, the diaphragm and intercostal muscles are the primary players in normal breathing. The abdominal muscles mainly assist with forced expiration, the pectoral muscles can aid during heavy breathing, and the quadriceps do not have a role in respiration.