Inhalations can take place only as a result of muscular activity. Exhalations are different: the lungs have the capacity to get smaller because their elasticity keeps pulling them, along with the rib cage, to a smaller size. And as alreadj mentioned, the size of the lungs follows the size of the chest in lockstep: anything that expands and contracts the chest also expands and contracts the lungs, whether it is lifting or compressing the rib cage, lowering or raisinp the dome of the respiratory diaphragm, releasing or pressing inward with the abdominal muscles, or allowing the elasticity of the lungs to draw in the chest wall.
The way in which the muscles of respiration accomplish breathing is more complex than the relatively simple way a muscle creates movements around a joint. Three main sets of muscles are active when you breathe normally: the intercostal muscles, the abdominal muscles, and the respiratory diaphragm. We'll start our discussion with the intercostal muscles.
the intercostal muscles
When we breathe, and in particular when we emphasize chest breathing, the short intercostal (between the ribs) muscles operate as a unit to expand
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