The diaphragm is a large dome shaped muscle located just below the lungs. As the diaphragm contracts, it flattens out of its dome shape, and creates a pressure difference that allows air to enter the lungs.

To the naked eye, when the diaphragm contracts, the stomach and abdominal contents tends to protrude outwards to make room for air the enter the thoracic cavity. This breathing strategy is often taught and exaggerated to help people become more efficient at breathing.

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