What muscles are primarily involved in forced breathing expiration?

• A. Scalenes
• B. External intercostals
• C. Internal intercostal muscles
• D. Diaphragm

Answer: (C)

In the context of forced breathing expiration, the internal intercostal muscles play a crucial role. During this process, the internal intercostals contract to pull the ribcage down and inward, which increases the pressure within the thoracic cavity and aids in pushing air out of the lungs. This muscle action is essential for actively expiring air, especially during vigorous activity or when a strong exhalation is required.

While the diaphragm is primarily involved in quiet breathing and assists during inhalation, it relaxes during forced expiration, making it less significant in this particular phase. The external intercostals are mainly responsible for elevating the ribs during inhalation. Scalenes primarily assist with elevation of the ribs, but their role is more pronounced during inhalation rather than forced expiration. Thus, the internal intercostal muscles are specifically designed to facilitate the mechanics of forced expiration efficiently.