Which muscle primarily aids in inhalation at rest?

The diaphragm is the primary muscle responsible for inhalation at rest. During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity. This results in a decrease in intrathoracic pressure, causing air to flow into the lungs. The diaphragm operates as a dome-shaped muscle, and its contraction creates the necessary pressure gradient for efficient breathing. Its pivotal role in normal, restful breathing makes it essential for maintaining proper gas exchange and respiratory function in the body.

The other muscles listed typically contribute to different aspects of respiration or movements and are not the primary drivers of quiet inhalation. For example, the transversus abdominis and rectus abdominis are primarily involved in exhalation or forceful breathing, while the external obliques assist with trunk rotation and lateral movements rather than being the main muscles for inhaling air into the lungs.