Proposed identification of physiological classification and theoretical mechanisms of yogāsanas

Yoga in the theoretical and practical form is now accepted all over the world, by the researchers as well as by the general population. Yogāsana or Yogic postures are one of the main foundations of practical yoga. Mechanisms of Mediation and Prānāyāma has already been established. In this article, the author is for the first time proposing physiological classification of Yogāsana i.e. (a) Stretch (b) Contraction (c). Neuromuscular Coordination (d) Sense Reduction (e) Spine Brain Activation. In support of this physiological classification author has proposed five hypothetical theories i.e. (i) Stretch Relaxation Awareness (ii) Contraction Relaxation Awareness (iii) Ballastic Contraction Relaxation Awareness (iv) Sensory Motor Function Awareness and (v) Vital Energy Flow Awareness to understand the underlying mechanisms of Yogāsana practice and to explain its benefits.


Yoga and Yogasana (Yogic posture)
Yoga is an ancient Bharatian (Indian) and Hindu culture. Archaeological evidence of Yoga seals (3300 BC) were excavated from the Harrapan civilization or Indus valley civilization [1e6]. The Vedas, world's oldest literature (2500 BCE) and Upanishads eluminated the wisdom of Yoga from the time of Vedic period [7,8]. Yoga culture was an essential part of Vedic tapabana ashramic educational system and in daily life from that time. Ram ayana and Mah abh arata the historical marvel of India recognised the practice and benefits of Yoga in Chatur a shramas of life: Brahmacharya-(celibate student hood and life building time, up to the age 25 years); G arhasthya (house holder stage and family life up to the age of 50 years); V aṇaprastha (detachment from the family life, up to the age of 75 years); and (complete detachment and surrender to the God, after the age of 75 years). In the time of Mah abh arata, Sr ımadbhagabadg ıt a, the conceptual gist of Vedas and Upaniṣhads, was written with all its 18 chapters' names attached with Yoga. It was the first time, Yoga was elaborated for general population and through it the general population received direction to cope with this world. G ıt a described the four main paths of life: J n ana Yoga (Wisdom seeker); Bhakti Yoga (Devotion maker); Karma Yoga (Selfless worker) and Dhy ana Yoga (Practical experiencer) to achieve success and peace in life. Takshashila university (600 BCE), the world's oldest University and Nalanda, another ancient university of India introduced compulsory Yoga in all their educational curriculums. During and after Bauddha and Jain period (500 BCE) Yoga was accepted by all spheres of life and people practiced Yoga regularly for their physical, mental, and spiritual wellbeing.
Ayurveda, the world's oldest record of medical practice [2,6] is ancient Indian medicinal system. Ayurveda meaning the science of long and healthy life, describes human being as the combination of body, mind, and soul. It prescribes Vy ayama (exercise) for the body and Yoga for mind and soul [9,10]. However, in the Ayurvedic text Yoga has been discussed only with few slokes (opharisms) and strongly recommended it as a specialized area [11]. Dhy ana Yoga or R aja Yoga was explained in a structured form in 'Yoga Sutra' written by the Sage Patanjali [12]. In this text had been described in eight limbs (Ast aṅga Yoga): Yama (Social discipline); Niyama (Individual discipline); Asana (Yogic postures); Pr aṇ ayama (Control of the vital energy through breathing); Praty ah ara (Withdrawal of sense organ); Dh araṇ a (Concentration); Dhy ana (Deep concentration) and Sam adhi (Deepest concentration). The detail description of Yogas ana (Yogic postures), the third limb of Astranga Yoga was found in the ancient Hatha Yogic text: Hatha Yoga Prad ıpik a [13]; GhrendaSamhit a [14]; Shiva Samhit a [15]; Vaśiṣṭhasa _ mhit a [16] and Haṭharatn aval ı [13] with the description of eighty four yog asanas. Scientific description with classification on Yog asana has been available in the modern literature [17e19]. In the most authentic way, Iyengar [20] described with two hundred Yogic postures. Both the ancient and modern literature on Yog asana claim that it improves wellbeing and can be effective for therapeutic purposes. The aim of this article is to propose physiological classification and theoretical mechanisms to understand Yog asana, in its practices.

Proposal of classification of Yogasana: On the basis of physiological functions
Yog asana have been classified by the authorities as meditative and cultural postures including relaxation posture [17]; along with meditation, standing, back bending, forward bending, spinal twisting, inverted, balancing poses [18]; standing, sitting, prone, supine, topsyturvy and relaxation postures [19]; and primary, intermediate and advance postures [20]. The author is actively involved in Yoga research for past 30

Stretch relaxation awareness theory
The author proposes that some asanas can be classified as 'Stretch' for example Pa scimott asana, Bhujaṅg asana, Salabh asana etc. At the time of stretching muscles spindle (stretch receptors) could be activated and after releasing these asanas same area would be relaxed than before. These functions will activate sensory and motor cortex. Body and breathing awareness will activate more brain parts to be engaged in this process. So, the concentration is developed automatically to maintain these postures.

Contraction relaxation awareness theory
In this theory, golgi tendon organ (GTO), another mechanoreceptor is targeted. Some Yog asanas can be grouped as 'Contraction' for example May ur asana, Utkat asana etc. At the time of performing these asanas fullest contraction could be focused on the related muscles. As a result, the GTO is activated and after releasing same area is relaxed much more. This process also activates the sensory-motor cortex. At the same time body and breathing awareness activates many other regions of the brain and enables concentration.

Ballistic contraction relaxation awareness theory
In this theory, the author would like to highlight vestibular apparatus in the inner ear and pacinian corpuscles present in the skin. Some balance or 'Neuromuscular Coordination' Yog asana like Vṛkṣ asana, Garuḍ asana, Natar aj asana etc. could activate these two receptors with their related sensory motor and other cortical areas. Also these type of asanas should activate lower brain or Cerebellum for coordination and body awareness. The Pons and Medulla areas are also involved for monitoring, the breathing awareness. Together, these activations may develop more concentration because many parts of the brain are involved in these balance type of Yog asana.

Sensory motor function awareness theory
In the fourth theory, the author proposes relaxation asanas or 'Sense Reduction type' asanas such as Shav asana, Adv asana, Makar asana etc. Here, the sensory motor nerve activity is forcefully reduced. So, the sensory-motor awareness in the cortical areas is slowly diminished. Also, by detracting and diverting all the external and internal sensory motor organs' activity these types of asanas could produce relaxation feelings.With this breathing awareness makes the person more aware about the vital activity of the body and beyond. Specially, the Midbrain area i.e. the filtering unit of sensory motor information has been deactivated and feeling of relaxation is persisted.

Vital energy flow awareness theory
The fifth proposed group in this article is 'Spine-Brain Activation'. In this group of asanas also called as meditative posture like Padm asana, Sukh asana, Siddhasana, and Svastik asana etc. Here, the spine and head should be erect to allow all neural impulses and vital energy to flow smoothly from the lower part of the spine to all areas of the brain and back to the lower part again. In these type of meditative postures, all the somatic and subtle autonomic neural awareness and vital organ awareness are subsided. Brain and spine level electrical activity and energy cost is reduced. But the higher cortical activity increased. Also in these type of asanas one may feel the PranaVayu (vital energy) in the different parts of the body and Chakras (energy wheels) in the spine and brain areas. One can relate individual energy with cosmic energy.

Conclusion
Yoga with all its forms (practical and theory) is now accepted globally. Yog asanas or Yogic postures are one of the pillars of the practical Yoga foundation. Analysis of mechanisms of meditation and pr aṇay ama has already been established. Yog asana effect in the human psychophysiological areas and its underlying mechanisms are not yet been identified. In this article, the author classified Yog asana from the physiological point of view i.e.Stretch, Contraction, Neuromuscular Coordination, Sense Reduction and Spine Brain Activation for the first time. To support the physiological classification the author has also for the first time proposed five theories i. Stretch Relaxation Awareness ii. Contrction Relaxatation Awareness iii. Ballistic Contraction Relaxation Awareness iv. Sensory-Motor function awareness and v. Vital Energy Flow Awareness to understand the underlying mechanisms of Yog asna practices. All these hypothetical theories should be examined by scientific protocols and methods for final conclusion.