Yoga is the science of entire creation. Sun, moon, earth, water, sky, fire as well as human body are various aspects of creation; yoga is the sum total of it. What is the force that powers the various aspects of creation, that makes them function, that is the subject of yoga.
When you do yoga under a guru, you start interacting with these various elements and forces, and slowly you become one with them. Take for instance the five elements. We know the body is made up of such elements, yet we cannot see them. As you do higher practices of yoga, you start realising all these in your body and understand their basis. Then the elements listen to you and follow you.
Yoga is often mistaken as a healing system of the body. Actually, it is the sum total of yam, niyam, asan, pranayam, pratyahaar, dhaarna, dhyan and samadhi. Asan and pranayam as detailed in yogsutras are not to cure diseases; Patanjali says sthir sukham asanam (a posture in which you are still). Stillness here refers to inner and outer silence achieved by silencing the vrittis of mind; experiences of yoga follow.
Let us take up the science of pranayam as an example. Today, there is no dearth of masters and teachers selling pranayam as an exercise to increase oxygen supply to the body and boost adrenalin. The fact is pranayam does not pertain to the physical body or annamaya. It is a salutation to prana, and prana runs in the pranamaya kosha, which directly affects the annamaya.
When you perform a pranayam, the oxygen levels reduce. In the lungs, there are tiny sacks called alveoli where exchange of gases happens.
For the absorption of gases by alveoli, a difference in pressure is required for a specific time period. Pranayams like nadi shodhanam equalise this pressure and as a result diffusion of gases does not happen.
Even in a hyper-pranayam like bhastrika and kapalbhati, the movement is so fast that there is no time for absorption of gases. So, oxygen supply reduces, and carbon dioxide levels increase.
The process of pranayam is triangle. The kundalini energy is in the form of an upward pointing triangle at the mool chakra. If you notice, in a pranayam, the movement of breath is in a triangular manner. There is an erectile tissue in our nose, which inflates when there is more blood flow. You might have observed that when you are sexually more active, at times the nose blocks, what is called the honeymoon nose, it is because of the erectile issue inflation only.
In pranayam, you make a triangle and press the erectile tissue at the nose constantly on both sides. This triangle pushes the kundalini energy upwards, when optimum areas of brain are awakened.
The optimum activation happens when the three nadis—ida, pingala and sushumna—are balanced. Then the kundalini energy rises and spiritual experiences follow. That is pranayam.
As you go deeper into yoga, you realise that all that heavy things leave you, age doesn’t touch you, strength of the body increases. But for this, you have to go to an ashram, make a guru and do yoga, buying off the shelf is not going to get you that because what is sold is tied to maya, and what is tied itself cannot release you from your bondages.