Thoracic kyphosis, or the classic upper back slouching, can cause dramatic decreases in lung capacity and function. Below are some examples of thoracic kyphosis:
The lungs are positioned inside the rib cage and normal or optimal thoracic spine, rib, and scapula position are needed for normal breathing and full lung capacity. Here is how the NIH describes breathing:
"When you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. This increases the space in your chest cavity, into which your lungs expand. The intercostal muscles between your ribs also help enlarge the chest cavity. They contract to pull your rib cage both upward and outward when you inhale.
As your lungs expand, air is sucked in through your nose or mouth. The air travels down your windpipe and into your lungs. After passing through your bronchial tubes, the air finally reaches and enters the alveoli (air sacs).
When you breathe out, or exhale, your diaphragm relaxes and moves upward into the chest cavity. The intercostal muscles between the ribs also relax to reduce the space in the chest cavity. As the space in the chest cavity gets smaller, air rich in carbon dioxide is forced out of your lungs and windpipe, and then out of your nose or mouth.
Lung capacity is something that is important for professional and top level athletes where the difference between winning and losing is often less than 1%. But lung capacity is also important for all active individuals who need their full lung capacity to enjoy running, biking, skiing, hiking, gardening, golfing, and playing sports.
Decreased lung capacity caused by the poor posture of thoracic kyphosis puts in increased stress on the heart and can cause heart disease, such as cor pulmonale. Cor pulmonale is the abnormal enlargement of the right side of the heart as a result of a disease of the lungs. People with severe thoracic kyphosis have even been know to have died from cor pulmonale when left untreated.