The first known appearance of the word "yoga", with the same meaning as the modern term, is in the Katha Upanishad,[9][95] probably composed between the fifth and third century BCE,[96][97] where it is defined as the steady control of the senses, which along with cessation of mental activity, leading to a supreme state.[67][note 13] Katha Upanishad integrates the monism of early Upanishads with concepts of samkhya and yoga. It defines various levels of existence according to their proximity to the innermost being Ātman. Yoga is therefore seen as a process of interiorization or ascent of consciousness.[99][100] It is the earliest literary work that highlights the fundamentals of yoga. White states:

Onesicritus also mentions his colleague Calanus trying to meet them, who is initially denied audience, but later invited because he was sent by a "king curious of wisdom and philosophy".[108] Onesicritus and Calanus learn that the yogins consider the best doctrine of life as "rid the spirit of not only pain, but also pleasure", that "man trains the body for toil in order that his opinions may be strengthened", that "there is no shame in life on frugal fare", and that "the best place to inhabit is one with scantiest equipment or outfit".[107][108] These principles are significant to the history of spiritual side of yoga.[107] These may reflect the ancient roots of "undisturbed calmness" and "mindfulness through balance" in later works of Hindu Patanjali and Buddhist Buddhaghosa respectively, states Charles Rockwell Lanman;[107] as well as the principle of Aparigraha (non-possessiveness, non-craving, simple living) and asceticism discussed in later Hinduism and Jainism.[citation needed]
Yoga gurus from India later introduced yoga to the West,[15] following the success of Swami Vivekananda in the late 19th and early 20th century with his adaptation of yoga tradition, excluding asanas.[15] Outside India, it has developed into a form of posture-based physical fitness, stress-relief and relaxation technique.[16] Yoga in Indian traditions, however, is more than physical exercise; it has a meditative and spiritual core.[16][17] 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.[18]
Similarly, Brahma sutras – the foundational text of the Vedanta school of Hinduism, discusses yoga in its sutra 2.1.3, 2.1.223 and others.[121] Brahma sutras are estimated to have been complete in the surviving form sometime between 450 BCE to 200 CE,[122][123] and its sutras assert that yoga is a means to gain "subtlety of body" and other powers.[121] The Nyaya sutras – the foundational text of the Nyaya school, variously estimated to have been composed between the 6th-century BCE and 2nd-century CE,[124][125] discusses yoga in sutras 4.2.38–50. This ancient text of the Nyaya school includes a discussion of yogic ethics, dhyana (meditation), samadhi, and among other things remarks that debate and philosophy is a form of yoga.[126][127][128]
Śaradatilaka of Lakshmanadesikendra, a Shakta Tantra work 11th century CE "Yogic experts state that yoga is the oneness of the individual soul (jiva) with the atman. Others understand it to be the ascertainment of Siva and the soul as non-different. The scholars of the Agamas say that it is a Knowledge which is of the nature of Siva’s Power. Other scholars say it is the knowledge of the primordial soul." (SaTil 25.1–3b)[35]
The hymns in Book 2 of the Shvetashvatara Upanishad, another late first millennium BCE text, states a procedure in which the body is held in upright posture, the breath is restrained and mind is meditatively focussed, preferably inside a cave or a place that is simple, plain, of silence or gently flowing water, with no noises nor harsh winds.[102][103][100]
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