Shadanga Yoga

He (Shiva) is manifested first in the initial movement of that breath, which is only filled with life (pranamayah)
and then during breathing in and breathing out (prana),
which in exhaling, creates
and in inhaling, destroys.
In reality, this breath is residing in the heart of beings.
(Svacchanda T. 7.25) 

The Life Force, Prana
In the teachings of Yoga we find a description of an encompassing, all pervading and all penetrating life force. In Sanskrit it is called prana and the term does not only denote life force but the act of breathing as well. Prana, inspite of its all penetrating nature is readily available to us primarily  in the air we breathe and the food we eat.

According to the teachings of Yoga with the breathing and the food, gross as well as subtle substances are absorbed, distributed and circulated in the body in a huge network of pathways or channels (nadi).

We absorb lesser amounts of subtle energies along with our sense impressions as well. Aside from our intake of food, oxygen and sense impressions, subtle energies are derived from the impact of other natural elements of our environment on our organism. We derive prana whenever we come into contact with other living beings, the earth and vegetation as well as from the impact of energies like light and heat. Life energy is in constant movement, it contracts (sancocha) and expands (unmesha), it vibrates and pulsates (spanda). In the Philosophy of Yoga  the most subtle form of life energy manifests as  primal subtle sound and vibration (nada, dhvani), which is the origin of gross sounds, of speech, words (vac) and syllables (varna). 

Nadis
Besides the blood circulation, nervous system and lymphatic system, Yoga teachings describe a subtle network of channels, streams or veins that pervade the body, these are termed nadi. The body is filled with a large number of these channels that expand like the veins on a leaf and criss cross to form a large network. Clusters of nadis exist at  crossings or  points  of origin, where several nadis meet. At these places  important vital points are formend.  These are called wheels (chakras ) or lotus flowers (padma). The subtle energies that move in the nadis are differentiated into several forms, which are all called prana (lifeforce, breath) or vayu (wind) or pranavayu (vital winds) these energies move the vital fluids or dots (bindu) that flow in the channels.

Jatharaagni or Kundalini
Agni (heat , fire) is the aspect of the life force that appears in diverse varieties of energy, warmth or heat, as arousal, excitation and expansion and vibration. In the body it appears primarily in the form of digestive energy, sexual energy and body heat. In the terminology of yoga. Agni in the body is known as pranashakti (power of life) jatharagni (digestive or gastric fire) or kundalini (curled) and chandali (female outcast). In its subtle form this energy manifest as sound and speech (nada, dhvani) In Yoga practice the use of Mantras, especially Om and Hamsah serves to cause an immersion in this power.

Pranavayus
In the body the absorbed prana fulfils different functions, accordingly it differentiates into several gross forms. They are named differently according to the diverse functions they fulfil and the body region they occupy. Yoga discerns between five major and five minor forms. They are collectively called prana (breaths, vital forces) vayu (winds) or pranavayu (vital winds).

Bindus
Body fluids like blood, sperm, urine, digestive juices, lymph, as well as streams of diverse subtle substances, driven by the respective pranavayus, are flowing in the form of drops, or brilliant dots (bindu), inside the diverse channels or nadis of the body. The bindus are differentiated into various forms. They appear primarily as  male white dots,  female red dots and neutral mixed dots. The dots are differentiated as well into five types, according to the vital winds that drive them, and the body region they occupy, into five differently coloured varieties.

The Three Bodies
To get a better understanding of the interaction between gross and subtle substances and the flow of vital energies it is helpful to visualize the human being as possessing a layered structure, a gross, a subtle and a causal body.

1.) In the Yoga philosophy the gross body (sthula sharira) consists of the so-called five elements the Panchamahabhutas (earth, water, fire, air and space)

2.) The subtle body consisting of the five sense organs, the five major vital winds, the intellect (manas), awareness (buddhi) , and the resulting concept of a self (ahamkara).

3.) The causal body, called karana sharira is the origin of the other bodies. They are at rest in this body, existing merely as a potential in a germinal form.

When one is aware of the causal body, and the attention rests on it, the objects of perception and the perceiver himself, the subject appear no longer separated, but in an indissoluble unity. Once one becomes aware of this body the mind is unsullied by defilements (mala) and their causes (karana).

The three states of human perception
Each of the bodies correspond with one of three basic states of human perception. According to the  Yoga philosophy these three basic states of human perception are jagat, svapna and sushupti, the waking state, the dream state and deep sleep.

Pervading the three other states, there is an impersonal all penetrating awareness called the fourth state. It is acknowledged as the observer of the other three states. Called Turiya (the fourth) it is the witness of the impermanence and fluctuation between waking, dream state and deep sleep.

When the mind of the Yogi is constantly established in this awareness, and never overwhelmed by any of the other three states, this is called turiyatita, the state existing beyond even the fourth state. Some yogis therefore speak of altogether five mental states and five subtle bodies.

The three bodies and the three states
The gross body corresponds to the waking state, the subtle body corresponds to the dream state, therefore it is also called dream body or illusive body, the causal body corresponds to the deep sleep state.

Deep sleep is not a state of complete unconsciousness. When awareness can be maintained it is the pure state free of differentiations, that rest in itself. During waking state, the world of outer objects and during dream state the mental experiences , both appear as if they are separate from the self. During deep sleep these objects are not perceived as separate but as part of one continuous mind.

Asana the body posture, consist of maintaining awareness of the gross body and mindfulness of the breath, in the subsequent limbs of Yoga this awareness is widened and includes practices of mindfulness of the subtle and causal bodies.

In this way the location of consciousness is shifted. Full awareness of the gross body locates the mind in the subtle body, full awareness of the subtle body locates the mind in the causal body. When the Yogi becomes aware of all the three bodies his mind is located in the all surpassing causal body (Mahakaranasharira)

The path of Yoga consists of gradually becoming aware of the gross, subtle and causal bodies and their purification and merging (laya) by mindfulness.

Threefold Processes in the yogic body
In the subtle body as well as the gross body vital force is generated by a threefold process of grasping (assimilation), holding (processing) and the subsequent release, rejection or excretion of waste products.

Nutrients are extracted from the food and oxygen from the air during digestion and breathing while poisonous or waste products are excreted by defecation and exhalation. Subtle life force is similarly generated by absorption, processing and subsequent excretion of waste products.

Also our mind is constantly engaged in metabolic cycles of assimilation, processing and excretion or release of experiences. The digestion of experiences involves judgement and reflection, intellectual as well as emotional activity. The useful experiences are comitted to memory, what appears to be useless or burdening is excreted. From the food we primarily derive the gross, from the breathing, the perceptive and cognitive processes subtle life forces.

Desiring and grasping, holding unto and processing, subsequent denial, release or rejecting and excretion are basic energetic cycles of life that dominate individual existence, experience and perception. In the gross body as well as in the subtle bodies, during the emotional and intellectual functions it is of vital importance that this process is happening smooth harmonious and equipoised. Yoga practice purifies and regulates these processes.

The three forms of life force  in the body in Yoga and Ayurveda.
The life force manifests in the body in a  triple form:

1.) In the form of subtle life energies or winds (prana, vayu) that move the gross fluids and subtle substances through different networks of channels.

2.) In the form of several types of heat in the body, among others namely the heat of digestion named jatharaagni and sexual energy. When the prana manifests in the form of heat, it is known by the term pranashakti (power of life) kundalini (the crooked) or chandali (the fierce lady or female outcaste). It can be stimulated by certain yogic exercises.

3.) In the form of circulation of fluid and light drops, (bindu) in a gross form such as oxygen and nutrients in the blood, and other gross body fluids such as lymph and sexual fluids, and as corresponding light drops or subtle fluids of hot, (agni) cold (soma) and mixed (surya) nature in the subtle body.

These three types of life energy in Yoga teachings, that vitalise the body are known in the indian art of healing, Ayurveda, as three principles (doshas):

1.) vata (wind) corresponding to the yogic prana and vayu,

2.) pitta (heat) corresponding to the yogic agni, chandali or kundalini, and

3.) kapha (phlegm) corresponding to the yogic bindu.