Diaphragm and Muscles

Inhale:The diaphragm is attached to the sternum , lower parts of the rib cage and the spine. As the diaphragm contracts it increases in length and diameter thus expanding the lungs. The intercostal muscles help move the rib cage and assist in breathing.

Exhale: when not exercising not much effort is needed . But with exercise abdominal muscles contract , which raises the abdominal pressure, and push the relaxed diaphragm against the lungs causing air to be pushed out