The diaphragm contributes 60-75% of the tidal volume.

During inspiration, it flattens to push the abdominal contents down and the rib margin upwards and outwards, increasing the vertical and the transverse diameter of the thorax.

The diaphragm relaxes during expiration to move upwards. In forced expiration, the abdominal muscles increase the intra-abdominal pressure to push the diaphragm upwards.

The diaphragm has a range of movement of 1.5 cm during quiet breathing and up to 13 cm during deep breathing.