The biomechanics of breathing involve the function of all the primary and secondary respiratory muscles that are involved in respiration. These can be grouped into the respiratory tract, respiratory support muscles, the abdominal muscles.
The respiratory tract
Yoga practices can affect the function of both upper and lower airways. Neti kriya, a cleansing technique, allows the bathing of the nasal passage. Ujjayi breathing can reduce dead space in the lungs and increase this way, the surface of oxygen diffusion to the bloodstream. While many asanas facilitate the delivery of air in one part of the lungs by restricting it in another, allowing this way the utilization of the entire organ. Finally, the diaphragm which seats at the bottom of the lungs can also get stronger through breathing exercises and/or asanas.
The supportive muscles
Muscles, fascia, and neurons all play an active role in supporting our respiratory function. While these tissues, cells and organs are not always classified as “respiratory”, failure of their function means compromised breathing.
Supportive muscles above the rib cage
Scalenes and sternocleidomastoid are 2 pairs of muscles sitting on either side of our neck. Their recruitment is often considered synonymous with upper chest breathing. It is my observation that when these muscles, alongside the trapezius, are tight there is zero movement possible in the upper chest and upper back, limiting this way the expansion of the lungs in this area.
Supportive muscles below the rib cage
Psoas and quadratus lumborum are 2 pairs of muscles on either side of the spine that attach posteriorly to the diaphragm. Having reviewed 1,000s of papers I am yet to see these 2 muscles mentioned in publications as respiratory or secondary respiratory muscles. There are 2 reasons why I think their structure and function are pivotal in breathing:
- As they both attach to the diaphragm, when they are tight, weak, or uneven (between the left and right side) they will restrict the way the diaphragm moves.
- Both muscles play an important role in our posture. A compromised posture will most likely cause restrictions in our breathing.
This is an area of the respiratory function that often does not get much attention. Think for a second of an old man bearing more weight on one foot, maybe having one shoulder higher than the other. Or a woman with pronounced scoliosis. How would these postural asymmetries affect the ideal symmetrical movement of the rib cage and diaphragm? Or someone with pronounced thoracic kyphosis. Do you see how the movement of his diaphragm will be restricted (ref)?
It is my belief that yoga can improve the biomechanics of breath in most elements of this Venn diagram and it’s for that reason a lot of yoga practitioners with respiratory problems have benefited from practicing yoga without paying much attention to the volume of air they breathe which determines the biochemistry of respiration. At the same time, the benefits are amplified when someone pays equal attention to both qualities of breathing (ie. biomechanics & biochemistry).