Hatha Yoga is designed to gain in-depth understanding of our body and to unleash its power and strength to obtain our higher selves. To a Hath Yogi, the body is not a mere mass of living matter, but a mystic bridge between the spiritual and the physical being. Hatha-yoga is often regarded as physical or bodily yoga. Such an over simplistic view is mistaken if that is all hatha is considered to be; but it is certainly the case that hatha-yoga works very much "with" and "through" the body, and that its conceptual isolation of the body is crucial to Hatha`s theory and practice. This conceptualization, which involves whole `subtle` physiological dimension-forms, should be understood properly.

Kaya Sadhana
Kaya Sadhana is the Sanskrit term for the development or cultivation of the body for a spiritual purpose. Kaya Sadhana in Hath yoga has a typical meaning that explains, "Hatha-yoga does not seek mere transcendental experiences. Its objective is to transform the human body to make it a worthy vehicle for Self-realization." According to a yogic philosophy: the body, mind and senses constitute instruments or tools for the respective processes of: Experiencing the world and realizing our true nature. If these instruments are to work efficiently then it is important that the yogi maintains them in the best possible condition, and, furthermore, endeavors to strengthen and purify them to the utmost.

According to Yoga-Sutra achieving this goal results in beauty, gracefulness, strength, and robustness. Such a condition is said to proceed from sanyama (control) upon the `gross` and `subtle` elements. This implies that bodily perfection is viewed as a consequence of meditative discipline, although the relation between the two should perhaps` be better understood as one of mutual enhancement. Physical upliftment assist spiritual one and vice versa.

Multi-layered Body
The underlying practice of hatha-yoga is a conception of the human body that is highly complex. It is also considerably at odds with the standard western materialist model. Central to the yogic conception does the notion of the human beings comprise a series of layers` of substance, from the `gross` and `external` through to the `subtle` and `internal`. The personality matrix is also described in terms of progressively rarefied `bodies` (Sariras) or `sheaths` (Kosas). The notion of three bodily levels is described as:

1. The sthula-sharira is the gross external form, corresponding roughly to the physical body known to materialist science. This sharira is shed at the point of physical death, although the personality continues to exist, operating through the sukshma-sharira.

2. The sukshma sharira comprises an `inner` (Antahkaran) and an `outer` (Bahyakaran) instrument. Bahyakaran is the collective term for the five `sense capacities` (buddhindriya) plus five `action capacities` (karmendriya). This `subtle body` is capable of migrating from one Sthula-sharira to another, thus engendering the process of reincarnation; the world can only be experienced when both sthula- and sukshma-sharira are present.

3. The Karana-sharira or `causal body` is so-called because of its status as `the original embryo or source of the body`." It is not even remotely `body-like`, but may, rather, be equated with prakriti as the un-manifest potential for embodiment. It can also be called as mahat or buddhi, the initial evolutes of this unmanifest potentiality.

The second model of the multi-layered human being, which is also shared by Samkhya-Yoga and Vedanta, is known as pancha-kosa due to its distinguishing five (pancha) `sheaths` or `coverings` (Kosha). The human being is described as a conglomeration of five `selves`, each composed of a particular substance, principle or faculty. Each of these selves is characterised as an atman, although they should not be combined with the supreme parama atman, of which they are merely veils. In later texts the lesser` or `conditional` modes of self became known as koshas and are referred to respectively as:

(1) Annamaya-kosa: Anna literally means `food`, but may be taken to refer to all the substances ingested for the maintenance and sustenance of the physical body, including the physical gas particles of the air. Maya means simply `made of` or `constituted by`; so the Annamaya-kosa is `the sheath constituted by food`, i.e. the `gross` physical body corresponding to the Sthula-sharira.

(2) Pranamaya-kosa: The Pranamaya-kosa is `the sheath constituted by prana`. The Anna- and prana-maya-koshas should be thought of as occupying the same bodily space and form, only the latter is of a more subtle nature, Prana, about which more will be said in the following chapter, is the `vitality` or life-force` that infuses the body, giving it life and maintaining its organic structure. This sheath, in combination with the following two, corresponds to the sukshma-Sharira.

(3) Manomaya-kosa: The Manomaya-kosa is the `Manas-constituted sheath`. Manas is the lower mind and the organizer of sense data and caretaker of memories. Manas forms a `sheath` around the Self in the sense that, by attributing mental activity to the Self, one obscures its true nature and becomes falsely identified as a `thinking thing`. The reality being that the Self is transcendent of all mental states and processes.

(4) Vijnanamaya-kosa: Vijnana denotes the higher operations of intellect, and has been variously translated as `wisdom`, `understanding`, `ideation`, `awareness`, etc. Taittiriya-Upanishad states that vijnana permeates the functions of Manas, and thus the vijnanamaya-kosa may be regarded as prior to the Manomaya-kosa as it is `closer` to the Self. It discriminates or `shift` the subjective from the objective reality; yet, since vijnana is not itself Purusha, it remains a mistaken medium of self-identity which is a thing to be cautious about.

(5) Anandamaya-kosa: Anandamaya-kosa is said to be contained `within` the vijnanamaya-kosa, and has `joy as the head, Contentment as right arm, and delight the left, Bliss is the heart, and Brahman the foundation.` While the term ananda often refers to the state of absolute bliss, which stands outside of conditional emotions, it may also signify a lesser mode of enjoyment. When self-identity is placed in the Anandamaya-kosa, `the self, by nature devoid of the dichotomy of pain and pleasure, is mistaken to be happy or unhappy, suffering pain or enjoying pleasure. ` Ananda sheath is actually the appearance of a limited ecstasy, existing only as the opposite pole of unhappiness. Taking up this viewpoint, the ananda sheath veils the true nature of the Self-which is entirely self-sufficient. Beneath these coverings lies the source of all.

The Subtle Body
The basic consideration of Human Body in yogic knowledge is as:
(a) of the body as the site of discipline of self-enlightenment.
(b) The human being as a multi layered organism.

The human body is considered as a psychophysical complex, which can be schematized as a series of graded levels from the purely physical elements to the most refined aspects of mind. Beyond the ordinary physical senses, the subtle bodily aspect of the human being is held to comprise a matrix of thread-like `channels` (Nadis). These Nadis are the conduits for the `vital force` referred to variously as prana, svara, vata, vayu, etc. The hatha-yogi is expected to acquire a detailed knowledge of his subtle physiology to become sensitive to the movements of prana. He accomplishes this task by refining his awareness beyond the scope of the physical senses. On the hatha view, it is by controlling and redirecting these forces that greater mental clarity will be gained.

So it is written in Goraksa-Sataka that the yogi must be familiar with the six chakras, sixteen adharas (supports), 300000 Nadis and five vyomans in his own body in order that perfection (Siddhi) in yoga is achieved. The yogi must know his own body as a temple supported by a single column, with nine doors and five presiding deities in order that perfection in yoga is achieved. To understand the subtle body, one must have to understand the following forces:

Prana - With regard to the texts of Hatha-yoga Prana is the Sanskrit term for life, vigour, vitality, and is carried out by the physical `air` or `breath` inhaled and exhaled by the lungs. It is the sustaining force and nourishment for the whole universe. The Shiva-Samhita hints at there being innumerable modes of prana, but names only the ten principal ones. Five being primary i.e. associated with fundamental life-processes and called "pranadi" (vital airs/forces), and five being secondary i.e. associated with more superficial processes and called nagadi (bodily airs/forces).

Each of these Prana-Vayu represents an aspect of the body`s innate `intelligence` and is held to regulate a particular process that is ordinarily unconscious though entirely necessary for the preservation and flourishing of life. These processes may come increasingly under conscious control through the practice of yoga. When breathing techniques are combined with bodily contractions and mental concentration to, first, the Nadis are cleansed through which vital force flows. Then the flow is redirected intentionally.

Of the ten main types of prana, it is prana and apana that are regarded as the `highest agents`, and hence it is the operations of these two which hatha-yogis are most concerned to bring under their control. It is the ordinary tendency of apanas the governor of excretory functions to flow down-wards and out of the body, while prana flows upwards and is expelled with the breath. By means of the specially designed postures (asanas), bodily `seals` and locks` (Mudras and bandhas), and breath-retentions (Kumbhaka), the yogi aims to prevent the escape of this vital force and to unify and retain it within the central channel of Sushumna Nadi.

Nadis - Nadi is the feminine form of "Nada", both terms denoting a tube, stalk or channel. Such channels may include veins, arteries, nerve Fibres and other bodily vessels, but, in the context of yoga physiology, Nadi refers specifically to conduits of prana. The number of nadis in the subtle matrix permeating the human organism is given variously in the manuals of hatha-yoga ranging averagely on 300,000 to being uncountable, like the veins of an asvattha leaf. The theory of Nadi also incorporates the conception of `tides` or `currents` of prana. They are the carrier of this vital energy, and pathway of Kundalini Shakti when evoked. The study of this aspect of vital force is often termed "svara-yoga", svara meaning `sound` and referring both to the subtle sound made by prana as it passes in and out of the body and to the prana it-self.

The seven Chakras - In the context of human subtle physiology, Chakra signifies a `centre` or `vortex` of `force` or `energy` situated at various junctions throughout the subtle matrix of nadis. It is considered that, just as there are thousands of nadis, so also are there thousands of chakras, although comparatively few of these are mentioned in the yoga literature. Chakras as the `centres`, `accumulators`, or `transformers` of vital force in the subtle body are symbolized by many representations. At the very least, such signs or symbols provide considerable assistance to the yogi in so far as they facilitate the concentration of attention upon, or within a particular region of the subtle matrix.

It also helps a yogi to understand the nature and various aspects related with the chakras. In the absence of such imagery, there would be much less to focus upon and to `draw the mind inwards`. The specific shapes, colours, sounds, and so forth, connected with each chakra are held to furnish an accurate representation. The tantric methodology deals majorly in the awakening of the proper senses of the related concentration point.

Kundalini Energy - Kundalini means `she who is coiled` and Shakti means `power`. Therefore, Kundalini-Shakti stands for the `coiled` or `spiral power`, often also known as `Serpent power`. This is the powerful force which when evoked transcends our being and self. Understanding these vital cosmic forces is a must for any Yogi to deal with the infinite potential in a human body, that when stirred up cause them to cross all the barriers and reach enlightenment.

Kundalini is a force so powerful as to be considered the source of all manifestation. There is more than one specific locus in the bodily matrix that harbors a strong potential for stimulating or accessing that force, and one or other of such loci may be the object of attention in particular hatha techniques. The presence of a range of `power access points` could be one reason for disagreements in hatha texts concerning Kundalini`s initial location. The aim of hatha-yoga is to first purify the nadis to facilitate the improved flow of prana, and then to induce the arousal and upward-movement of Kundalini. The activation of this otherwise latent but extremely powerful force is bound to create a profound transformation of the yogi. Not to mention his sublimation of his or her ordinary sense of identity.

Several interpreters have attempted to relate the phenomena of the subtle bodily matrix to those with physical anatomy of human body and in the context of modern biological science. While the chakras are not to be identified with the physical plexuses of the nervous system, they are nevertheless connected with, and in a physical sense represented by them. Many have gone further and have indeed tried to draw an equation between the nadis and chakras on the one hand, and the Fibres and plexuses of the physical nervous system on the other. The web of nadis can be equated with the physical nervous system, the chakras with `clusters of intersecting nerves` and prana with nerve energy.

It remains an unfortunate fact that the phenomena associated with the human being below the level of the outer body are generally unsusceptible to physical measurement. This is the reason for those non-yogis who have not yet acquired direct perception of the subtle organs, and who are not naturally gifted with psychic abilities, the existence of such phenomena can only be inferred or accepted on faith. But the bottom line remains that it is important to get some notion of this aspect of our subtle body to gain proper understanding of hatha yoga techniques and principles.