This is an excerpt from Yoga Anatomy-2nd Edition by Leslie Kaminoff & Amy Matthews.
Yoga Lessons From a Cell
Cells are the fundamental building blocks of life, from single-celled plants to multitrillion-celled animals. The human body, which is made up of roughly 100 trillion cells, begins as two newly created cells.
A cell consists of three parts: the cell membrane, the nucleus, and the cytoplasm. The membrane separates a cell's internal environment, which consists of the cytoplasm and nucleus, from its external environment, which contains the nutrients that the cell requires.
After nutrients have penetrated the membrane, they are metabolized and turned into energy that fuels a cell's life functions. An unavoidable by-product of all metabolic activity is waste, which must get back out through the same membrane. Any impairment to a cell's ability to let nutrients in or let waste out results in death by starvation or toxicity. The yogic concepts that relate to this functional activity of the cell are prana and apana. The concepts that relate to the structural properties of the membrane that support that function are sthira and sukha.
Prana and Apana
The Sanskrit term prana is derived from pra-, a prefix meaning before, and an, a verb meaning to breathe, to blow, and to live. Prana refers to what nourishes a living thing, but it has also come to mean the action that brings the nourishment in. Within this chapter, the term will refer to the functional life processes of a single entity. When capitalized, Prana is a more universal term that can be used to designate the manifestation of all creative life force.
All living systems require a balance of forces, and the yogic concept that complements prana is apana, which is derived from apa, meaning away, off, or down. Apana refers to the waste that's being eliminated as well as the action of elimination. These two fundamental yogic terms—prana and apana—encompass the essential functions of life on every level, from cell to organism.
Sthira and Sukha
If prana and apana are expressions of function, what of the structural conditions that have to exist in a cell in order for nutrition to enter and waste to exit? This is the function of the membrane—a structure that must be just permeable enough to allow material to pass in and out (see figure 1.1). If the membrane is too permeable, the cell loses integrity, causing it to either explode from pressures within or implode from pressures without.
In a cell, as in all living things, the principle that balances permeability is stability. The yogic terms that reflect these polarities are sthira and sukha. In Sanskrit, sthira can mean firm, hard, solid, compact, strong, unfluctuating, durable, lasting, or permanent. Sukha is composed of two roots: su meaning good and kha meaning space. It means easy, pleasant, agreeable, gentle, and mild. It also refers to a state of well-being, free of obstacles.
All successful living things must balance containment and permeability, rigidity and plasticity, persistence and adaptability, and space and boundaries. This is how life avoids destruction through starvation or toxicity and through implosion or explosion.
Successful man-made structures also exhibit a balance of sthira and sukha. For example, a suspension bridge is flexible enough to survive wind and earthquakes, but stable enough to support its load-bearing surfaces. This image also invokes the principles of tension and compression.
Sukha also means having a good axle hole, implying a space at the center that allows function. Like a wheel, a person needs to have good space at his or her center, or functional connections become impossible.
Human Pathways of Prana and Apana:
Nutrition In, Waste Out
The body's pathways for nutrients and waste are not as simple as those of a cell, but not so complex that we can't easily describe them in terms of prana and apana.
Figure 1.2 shows a simplified version of our nutritional and waste pathways. It shows how the human system is open at the top and at the bottom. We take in prana—solid and liquid nourishment—at the top of the system. These solids and liquids enter the alimentary canal, move through the digestive process, and, after a lot of twists and turns, move down and out as waste matter. This is the only way waste can go, because the exits are at the bottom. It is clear that the force of apana, when acting on solid and liquid waste, must move down to get out.
Prana also enters our bodies in gaseous form: the breath. Like solids and liquids, it enters at the top, where it remains above the diaphragm in the lungs (see figure 1.3), exchanging gases with the capillaries at the alveoli. The waste gas in the lungs needs to be expelled, but it gets out the same way it came in. The force of apana, when acting on respiratory waste gas, must move up to get out. Apana must be able to operate freely both upward and downward, depending on what type of waste it acts upon.
The ability to reverse apana's downward action is a basic and useful skill acquired through yoga practice, but not something most people are able to do without training. People are accustomed to pushing down to operate their apana. Many have learned that whenever something needs to be eliminated from the body, the body must squeeze in and push down. That is why, when most beginning students are asked to exhale completely, they activate their breathing muscles as if they are urinating or defecating.
Sukha and Dukha
Prana and apana must have a healthy reciprocal relationship in the body; thus, the body's pathways must be clear of obstructing forces. In yogic terms, our breathing bodies must be in a state of sukha, translated literally as good space. Bad space is referred to as dukha, which is derived from dus, meaning bad, difficult, or hard, and kha, meaning space. It is generally translated as suffering, uneasy, uncomfortable, unpleasant, and difficult.
This model points to the fundamental methodology of all classical yoga practice, which seeks to uncover and resolve blockages or obstructions (kleshas1) to improve function. Essentially, when we make more good space our pranic forces flow freely and restore normal, healthy function.
The modern master of yoga therapy, T.K.V. Desikachar, has often said that yoga therapy is 90 percent waste removal.
Because exhalation is an action of removing waste from the system, another practical way of applying this insight is that if we take care of the exhalation, the inhalation takes care of itself. If we get rid of the unwanted, we make room for what is needed.
Read more from Yoga Anatomy, Second Edition By Leslie Kaminoff, Amy Matthews.