Which muscles are primarily involved in respiration when at rest?

The diaphragm and external intercostal muscles are primarily responsible for respiration at rest. The diaphragm is a dome-shaped muscle that resides at the base of the thoracic cavity and is the main muscle of respiration. During inhalation, it contracts and moves downward, creating a negative pressure in the thoracic cavity, which allows air to flow into the lungs.

The external intercostal muscles, located between the ribs, assist in deepening the inhalation by elevating the rib cage and expanding the thoracic cavity further. This coordinated action of the diaphragm and the external intercostal muscles is effective during quiet breathing, which is the typical state when the body is at rest.

The other muscle groups listed are involved in different aspects of movement and respiration. The scalenes and sternocleidomastoids are accessory muscles used during more vigorous breathing or during exercise, while the rectus abdominis and internal obliques come into play primarily during forced exhalation, such as during heavy exercise or coughing. The transverse abdominis and serratus anterior also assist in specific movements but are not the primary muscles engaged during rest. Thus, the diaphragm and external intercostal muscles are the primary contributors to the respiratory process during quiet breathing, making this