Your diaphragm is a weird, dome-shaped muscle. It contracts down, actively flattening out and creating a vacuum that the external air fills. Next, it relaxes back up to its original dome-shape as you exhale passively. Along with the diaphragm, your intercostal muscles contract to lift your ribs slightly, and there is even a small life of your collar bones at the accessory muscles of your shoulders, neck and chest engaged. In yoga, this is 3-phase breath. | YOGABODY