Breathing moves air into and out of the lungs and facilitates gas exchange. The human body requires oxygen to break down foods during cellular respiration, thus releasing energy for body structures to use. With less oxygen, the body performs less efficiently. Voluntary apnea is the medical term for holding your breath, and the action has various effects on the human body. Many athletes practice voluntary apnea to train, and many meditation practices believe that breath-holding is beneficial.
Human lungs are not capable of pulling in air themselves. Instead, the diaphragm contracts and moves downward to increase the available volume in the chest. Humans can force themselves to breathe using certain accessory muscles. The lungs then inflate, allowing air to enter and fill air sacs called alveoli. Oxygen from the air in the alveoli can then pass to the blood vessels while carbon dioxide moves into the alveoli from the blood vessels. Oxygen-rich blood then travels to the heart, which pumps it throughout the body. To exhale, the diaphragm relaxes along with the intercostal muscles. This contracts the lungs and forces out air rich in carbon dioxide.
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