The three main groups of muscles used for breathing are the diaphragm, intercostal and accessory. Adopting diaphragmatic breathing is important for reducing hyperventilation.
The diaphragm is a strong, thin, ﬂat sheet of muscle which separates the chest from the tummy and is shaped like the dome of an umbrella. To breathe in, the Medulla Oblongata, located in the brain, sends a message to the diaphragm to move downwards. This creates a negative pressure in the chest cavity, called the thorax, which causes the lungs to draw in air to equalise this negative pressure. The downward movement of the diaphragm on the abdominal contents causes the stomach to expand a little as we breathe in.
Two activities which result in poor use of the diaphragm are bad posture and mouth breathing. Mouth breathers tend to breathe using their upper chest muscles. Surprisingly, the upper chest does not expand outwards but rises and falls with each inhalation and exhalation.
Switching to nasal breathing is the ﬁrst step in changing to diaphragmatic breathing. Poor posture has a negative impact on breathing and being slouched over a desk all day will not help. At each workshop, I demonstrate how posture inﬂuences breathing.
Note: This bell jar experiment illustrates the central role which the diaphragm performs during breathing. To breathe in, neurons within the brain stimulate the diaphragm to contract (move downwards 1 cm to 10 cm) which enlarges the chest cavity or thorax. This causes a negative pressure (as in the ﬁrst diagram) resulting in inhalation – until the pressure in the alveoli within the lungs equals atmospheric pressure. At the end of inspiration, the nerves to the diaphragm cease ﬁring and so the muscles involved in respiration relax. This ‘compresses’ the air within the alveoli, and this causes an exhalation. It is the movement of the diaphragm from the relaxed position to the contracted position which causes the tummy to move out, and that from the contracted position to the relaxed position which causes the tummy to move in.
‘Deep’ versus ‘big’:
The correct interpretation of the word ‘deep’ in this context is breathing using the diaphragm. A deep breath means using the depth of the lungs. There is a misconception that a deep breath is a big breath. A deep breath can be a big or a small breath. What is important is that the diaphragm moves. From time to time, I ask people to take a deep breath and the response is almost always huge inhalations of air – often through the mouth. Not only is this breathing big, it is also shallow as chest muscles predominate and only the top parts of the lungs are ventilated.