What muscular action is primarily responsible for achieving forced expiration?

• A. Diaphragm contraction
• B. Abdominal muscle contraction
• C. Intercostal muscle contraction
• D. Thoracic expansion

Answer: (B)

Forced expiration primarily involves the contraction of the abdominal muscles. During this process, the abdominal muscles contract to push the diaphragm upward and compress the thoracic cavity, which increases the pressure in the lungs and helps to expel air forcefully. This muscular action is crucial for activities that require rapid or forceful breathing, such as during vigorous exercise or coughing.

The interplay with the diaphragm is important, as its contraction during normal inhalation facilitates expansion of the lungs, but during forced expiration, the abdominal muscles play a dominant role in actively reducing the volume of the thoracic cavity. Other muscle groups may assist in forced expiration, such as the internal intercostal muscles, but the primary action is from the abdominal muscles, which significantly contribute to this forceful expulsion of air.