What best describes the movement of the thoracic wall during normal breathing?

During normal breathing, particularly during inhalation, the thoracic wall expands as the diaphragm contracts and moves downward, and the intercostal muscles pull the ribs upward and outward. This expansion increases the overall diameter of the thoracic cavity. As a result, the lungs are able to fill with air more effectively, facilitating efficient gas exchange.

The increase in diameter is essential for creating a negative pressure within the thoracic cavity, which allows air to flow into the lungs. Consequently, during normal inhalation, the diameter of the thoracic wall indeed increases as part of this process.

In contrast, the other options do not accurately reflect the mechanics of normal breathing. The diameter decreasing or remaining the same would not accommodate effective inhalation, and the statement about the chest sinking does not account for the active expansion associated with breathing in. Understanding this aspect of thoracic movement is crucial for anyone studying or practicing Pilates or other forms of movement and breathing exercises, as it directly relates to how breath support plays a role in stabilization and movement efficiency.