Which muscle is used for inspiration during both eupnea and forced breathing?

• A. Rectus abdominus.
• B. Sternocleidomastoid.
• C. Serratus anterior.
• D. External intercostal muscles.

Answer: (D)

Verified step by step guidance

1. Understand the process of inspiration: Inspiration is the phase of breathing where air is drawn into the lungs. During eupnea (normal, quiet breathing), certain muscles are primarily responsible for this action.
2. Identify the primary muscles involved in eupnea: The diaphragm is the main muscle used during eupnea, but the external intercostal muscles also play a significant role by elevating the ribs and expanding the thoracic cavity.
3. Consider forced breathing: During forced breathing, additional muscles are recruited to increase the volume of air inhaled. These include accessory muscles such as the sternocleidomastoid and scalene muscles.
4. Focus on the external intercostal muscles: These muscles are involved in both eupnea and forced breathing. They work by elevating the ribs, which increases the volume of the thoracic cavity and facilitates the inflow of air.
5. Conclude the role of external intercostal muscles: Given their involvement in both normal and forced inspiration, the external intercostal muscles are crucial for effective breathing across different conditions.