The Bhagavad Gita ('Song of the Lord') is part of the Mahabharata and also contains extensive teachings on Yoga. According to According to Mallinson and Singleton, the Gita "seeks to appropriate yoga from the renunciate milieu in which it originated, teaching that it is compatible with worldly activity carried out according to one's caste and life stage; it is only the fruits of one's actions that are to be renounced." In addition to an entire chapter (ch. 6) dedicated to traditional yoga practice, including meditation, it introduces three prominent types of yoga:
Classical yoga incorporates epistemology, metaphysics, ethical practices, systematic exercises and self-development techniques for body, mind and spirit. Its epistemology (pramana) and metaphysics is similar to that of the Sāṅkhya school. The metaphysics of Classical Yoga, like Sāṅkhya, is mainly dualistic, positing that there are two distinct realities. These are prakriti (nature), which is the eternal and active unconscious source of the material world and is composed of three gunas, and the puruṣas (persons), the plural consciousnesses which are the intelligent principles of the world, and are multiple, inactive and eternal witnesses. Each person has a individual puruṣa, which is their true self, the witness and the enjoyer, and that which is liberated. This metaphysical system holds that puruṣas undergo cycles of reincarnation through its interaction and identification with prakirti. Liberation, the goal of this system, results from the isolation (kaivalya) of puruṣa from prakirti, and is achieved through a meditation which detaches oneself from the different forms (tattvas) of prakirti. This is done by stilling one's thought waves (citta vritti) and resting in pure awareness of puruṣa.
Jain yoga has been a central practice in Jainism. Jain spirituality is based on a strict code of nonviolence or ahimsa (which includes vegetarianism), almsgiving (dana), right faith in the three jewels, the practice of austerities (tapas) such as fasting, and yogic practices. Jain yoga aims at the liberation and purification of the self (atma) or soul (jiva) from the forces of karma, which keep all souls bound to the cycle of transmigration. Like Yoga and Sankhya, Jainism believes in a multiplicity of individual souls which bound by their individual karma. Only through the reduction of karmic influxes and the exhaustion of one's collected karma can a soul become purified and released, at which point one becomes an omniscient being who has reaches "absolute knowledge" (kevala jnana).
Yoga gurus from India later introduced yoga to the West, following the success of Swami Vivekananda in the late 19th and early 20th century with his adaptation of yoga tradition, excluding asanas. Outside India, it has developed into a form of posture-based physical fitness, stress-relief and relaxation technique. Yoga in Indian traditions, however, is more than physical exercise; it has a meditative and spiritual core. One of the six major orthodox schools of Hinduism is also called Yoga, which has its own epistemology and metaphysics, and is closely related to Hindu Samkhya philosophy.
Yoga and Vedanta are the two largest surviving schools of Hindu traditions. They share many thematic principles, concepts and belief in self/soul, but diverge in degree, style and some of their methods. Epistemologically, Yoga school accepts three means to reliable knowledge, while Advaita Vedanta accepts six ways. Yoga disputes the monism of Advaita Vedanta. Yoga school believes that in the state of moksha, each individual discovers the blissful, liberating sense of himself or herself as an independent identity; Advaita Vedanta, in contrast, believes that in the state of moksha, each individual discovers the blissful, liberating sense of himself or herself as part of Oneness with everything, everyone and the Universal Self. They both hold that the free conscience is aloof yet transcendent, liberated and self-aware. Further, Advaita Vedanta school enjoins the use of Patanjali's yoga practices and the reading of Upanishads for those seeking the supreme good, ultimate freedom and jivanmukti.
Core: Yes. There are yoga poses to target just about every core muscle. Want to tighten those love handles? Then prop yourself up on one arm and do a side plank. To really burn out the middle of your abs, you can do boat pose, in which you balance on your "sit bones" (the bony prominences at the base of your pelvic bones) and hold your legs up in the air.