Depending on the amount of effort we exert, the act of breathing can be accomplished with the help of many muscles. The main muscle of breathing is a muscle called the diaphragm. A diaphragm is something that separates two structures. The diaphragm muscle separates the heart and lungs from the abdominal organs—with a double domed shaped sitting inside chest like a parachute. The diaphragm is also involved in non-respiratory functions, such as going to the bathroom and vomiting and it is intimately involved with my favorite muscle the psoas.
Calling this muscle the diaphragm is an interesting choice as it is one of many diaphragms in the body but the only one labeled as such. It is often referred to as the thoracic diaphragm as it resides at the base of the rib cage and thoracic spine.
There are a number of primary muscles for breathing. While the diaphragm should do about 75% of the work, the abdominal muscles as well as the intercostals muscles between the ribs also have a role.
The secondary muscles of breathing –designed to work when the body works harder—are the pectoral muscles (the chest), the trapezius, the sternocliedomastoid and the scalenes (all connect up into the head). The problem from my perspective is that due to poor posture, these secondary muscles are often doing the work of the primary muscles, especially the diaphragm.
Inhalation occurs when the diaphragm descends or the rib cage expands and brings the lungs along with them. The resulting suction pulls air from the mouth to the trachea and into the lungs. The exhale happens when the diaphragm is pulled back up by the connective tissue of the lungs. Muscle doesn’t retract in and of itself so the lungs actually have a protein called surfactant that essentially rubberizes them so that they shrink after expansion. This helps create the bellows action that should happen when the body works as designed.
Breathing is considered to be diaphragmatic when the diaphragm can descend on the inhale. This is an efficient type of breathing as it is likely to get air to the lowest part of the lungs where the blood resides. This is one of the reasons why inversions in yoga are so healthy. They mix the blood in the lungs so to that air and gas can circulate. If we are upright we need very efficient breathing in order to get oxygen into the whole of the lungs.
Thoracic breathing is when the ribcage expands more than the diaphragm descends. This requires more work for the same mixing of gas, blood and oxygen. To accommodate the greater effort, more oxygen is needed which means more work for the heart.
The next post will detail why our poor posture interferes with the successful functioning of the diaphragm.