diaphragm
Normal relaxed breathing is referred to as tidal volume. This is produced by the action of the diaphragm muscle only. It is also referred to as diaphragmatic breathing and is associated with a relaxed state.
The deep thorax muscles are the deep muscles of the thorax that promotes the inspiratory phase of breathing. When breathing the diaphragm contracts, producing a negative pressure, which forces are into the lungs.
These are diaphragm and externa intercostal muscles in quiet breathing and sternocliedomastoid ,sclene muscles,anterior serrati in heavy breathing
external/ internal intercostals
Ribs are for protection i think and diaphragm is the muscle controlling inhaling and exhaling. Also: the rib muscles can help the breathing process, which is useful when the diaphragm is weak, constricted, or to get an extra-big breath. Breathing from the diaphragm makes the belly move in and out as the lungs extend downwards. Breathing from the rib muscles makes the chest expand and rise.
For relaxed breathing, called tidal breathing, all you need is the diaphragm muscle.
external intercostals and the diaphragm
Diaphragm
The diaphragm and external intercostal muscles are primarily involved in changing the thoracic volume during breathing. The diaphragm contracts during inhalation to increase thoracic volume, while the external intercostal muscles help lift and expand the rib cage.
The primary muscles involved in normal breathing are the diaphragm and the intercostal muscles. The diaphragm contracts and moves downward, while the intercostal muscles between the ribs help expand the chest cavity, allowing air to be drawn into the lungs.
And the *diaphragm*