- the intercostal muscles contract, expanding the ribcage
- the diaphragm contracts, pulling downwards to increase volume of the chest
- pressure inside the chest is lowered and air is sucked into the lungs
When you exhale
- the intercostal muscles relax, ribcage drops inwards and outwards
- the diaphragm relaxes, moving back upwards to decrease volume of the chest
- pressure inside the chest increases and air is forced out ..