What causes the diaphragm to contract

The individual breathing movements

inhalation

When inhaling, a distinction is made between chest and abdominal breathing. When breathing in the chest, the intercostal muscles are tensed when you inhale. This lifts the ribs, and with them the chest, and enlarges the chest cavity. Since the lungs are firmly attached to the chest wall, the elastic lungs follow this expansion of space and expand. The lungs, which have been enlarged in this way, now suck in outside air, which flows in via the trachea and bronchi.

In abdominal breathing (diaphragmatic breathing), the diaphragm, which lies below the lungs between the chest and abdominal cavity and has the shape of a double dome, is tensed. The tension flattens the dome and the chest area is enlarged lengthways (downwards). The lungs attached to the chest expand accordingly (also downwards) and suck in outside air, which flows into the lungs. As the space below the diaphragm becomes smaller during abdominal breathing during the inhalation movement (flattening of the diaphragm), the abdominal viscera must be shifted downwards and push the abdominal wall forward.

In general, chest and abdominal breathing are combined, both deep and superficial. With increasing age and thus decreasing elasticity of the chest, abdominal breathing becomes more important than chest breathing.

exhalation

There is no active muscle tension when exhaling. The diaphragm relaxes and expands upwards again as a double dome, so that the chest cavity becomes smaller again. The lungs are pushed back and the air you breathe flows out of the lungs. When you exhale, the chest and abdominal muscles passively return to their original position due to their inherent tension (inherent elasticity).

Breathing movements under greater exertion

With increased inhalation, the diaphragm and the outer intercostal muscles are strongly tensed to further lift the chest. In the case of particularly high physical stress or bronchial asthma and other lung diseases, the so-called auxiliary breathing muscles (chest and shoulder girdle muscles) are also used. These muscle groups can develop their optimal effect through certain breath-relieving body positions in which the shoulder girdle is fixed. The exhalation following increased inhalation cannot, however, be increased beyond the resting position (into which the chest and diaphragm only sink passively).

The abdominal muscles and the inner intercostal muscles cause increased exhalation. The abdominal muscles pull the rib cage down, shrinking both the chest and the space below the diaphragm. However, the abdominal viscera cannot be displaced any further and press the diaphragm upwards - the lung space is thus considerably reduced. In addition, transverse abdominal muscles can pull in the abdominal wall and thus pull the diaphragm up even further.