In a tree, roots and the trunk form the foundation. Similarly, in the path of Yoga, the Yamas and Niyamas form the foundation. Further, the trunk divides itself into branches, likewise in the Aṣtānga Yoga, Asana is the branches.
Ᾱsana simply means posture. A posture becomes a āsana when one is comfortable, stable and in the posture for a long time.
Patanjali never really emphasis much on the Ᾱsanas; Patanjali defines Ᾱsana as Sthiramsukhamāsanam (PYS 2.46) meaning Ᾱsana is a posture in which one is comfortable, stable for a long time. In Haṭha Yoga, before performing or practicing postures, one has worship to Ᾱdinath (he instructs the knowledge of Yoga). Ᾱsanas are majorly described in the Haṭha Yoga Pradipika, Śiva Samhita and Gheranda Samhita.
Ᾱsanas are not merely gymnastic exercises. They are specific postures which open up the energy levels and produces mental equilibrium. When Ᾱsanas are practiced, steadiness is developed ensuring the free flow of the Prāṇa. When Prāṇa flows freely in the body, there are no blockages and toxins are removed from the body.
Ᾱsanas are very important as they make the body fit for the practitioner in the path of Sādhana. By practicing Ᾱsanas, the mind is also activated as one has to keep the body in alignment and this can be achieved only when the practitioner concentrates on the posture, body alignment and the breathing all at once. Any Ᾱsana before performing should be studied in the different aspects like distribution of weight, the geometry and this should be presented in the posture. The whole body, senses, mind and even consciousness are i nvolved in the process hence, ensuring the union of body with mind.
Ᾱsanas are an imitation of the nature. There is a saying that the number of Ᾱsanas is equivalent to the forms of life. Some of the Asanas are named after the plant kingdom, such as vrkśāsana and Padmāsana; named after tree and the flower respectively. Asanas are also named after animal kingdom; they include Asanas such as Makarāsana and Bhujangāsana named after the animals crocodile and cobra respectively. Ᾱsanas have also been inspired by great sages who have attained liberation in specific postures; they include Asanas such as Bhardwajāsana named after the sage Baradwaj and Ardha Matsyendrāsana named after Mastyendranath. Asanas are also named after gods e.g. Hanumāsana named after the lord Hanuma. Not all Ᾱsanas are described in Haṭha Yoga. Swami Swatmarama (the author of Haṭha Yoga Pradipika) carefully picks and describes a few of the Ᾱsanas which gives maximum effect in bringing a balance and preventing the fickleness of the mind. Ᾱsanas have also been inspired by great sages who have attained liberation in specific postures.
Lord Krishna gives a clear description in Bhagwad Gita about the way a Ᾱsana should be performed:
Śucou deśe pratiṣṭhāpya sthiramāsanamātmanaḥ
Nātyucitam nātinicam cylājinakuṣottaram. (Bhagwad Gita)
The meaning of the above verse is “the place to perform a Ᾱsana has to be clean, the seat neither too low nor too high. Then spread a white cotton cloth on kuśa grass and this becomes the preparation for Ᾱsana”. After the preparation is done, the Ᾱsana should be performed with ease and comfort but without any movement in the pose.
Patanjali says how one can master a Ᾱsana in the sūtra “Prayatnaśaithilyām anantasamāpattibhyām (PYS 2.47). According to which, the effort to perform the Ᾱsana becomes effortless, then one can perfect the Ᾱsana and one unite with the Supreme Being. Patanjali also gives the importance of Ᾱsanas by saying that when a Ᾱsana is correctly performed, the dualities of nature of body and mind, mind and soul seize to exist. When the Ᾱsanas are performed in this manner, the body cells are kept healthy and the physiological body is brought closer to the soul.
Ᾱsanas have immense therapeutic benefits. They tone the muscles, tissues, ligaments, joints and nerves and maintain a smooth functioning of all systems in the body. They bring a balance between sympathetic and para-sympathetic nervous systems. They increase the metabolism and bring harmony in the endocrine system. They improve blood and lymphatic circulation.
Lastly, Ᾱsanas should be performed with Bhakti and not as just mere form of exercise to attain a fit body, as this nurtures and tunes our body in turn our mind in the path of Yoga and as B.K.S Iyengar quotes “True Ᾱsana is that in which the thought of Brahman flows effortlessly and instantly through the mind of a Sādhaka”.