Which muscles make fine adjustments in the abdominal cavity to support phonation and speech breathing by altering intra-abdominal pressure?

• A. Internal intercostals
• B. External intercostals
• C. Muscles of the abdominal wall
• D. Diaphragm

Answer: (C)

The muscles of the abdominal wall are responsible for making fine adjustments in abdominal cavity pressure. When they contract, they compress the abdominal contents and increase intra-abdominal pressure. That pressure helps regulate the flow of air out of the lungs and up to the vocal folds, providing the subglottal pressure needed for phonation and smooth, controlled speech breathing. This coordination allows precise control over how quickly and how much air is released, which is essential for sound quality and timing in speech.

The diaphragm mainly drives inspiration by expanding the thoracic cavity, not by fine-tuning abdominal pressure. The intercostal muscles adjust rib cage movement for breathing but aren’t the primary source of abdominal pressure changes.