Krishnamacharya in the context of "Natarajasana"

An āsana (Sanskrit: आसन) is a body posture, originally and still a general term for a sitting meditation pose, and later extended in hatha yoga and modern yoga as exercise, to any type of position, adding reclining, standing, inverted, twisting, and balancing poses. The Yoga Sutras of Patanjali define "asana" as "[a position that] is steady and comfortable". Patanjali mentions the ability to sit for extended periods as one of the eight limbs of his system. Asanas are also called yoga poses or yoga postures in English.

The 10th or 11th century Goraksha Sataka and the 15th century Hatha Yoga Pradipika identify 84 asanas; the 17th century Hatha Ratnavali provides a different list of 84 asanas, describing some of them. In the 20th century, Indian nationalism favoured physical culture in response to colonialism. In that environment, pioneers such as Yogendra, Kuvalayananda, and Krishnamacharya taught a new system of asanas (incorporating systems of exercise as well as traditional hatha yoga). Among Krishnamacharya's pupils were influential Indian yoga teachers including Pattabhi Jois, founder of Ashtanga (vinyasa) yoga, and B.K.S. Iyengar, founder of Iyengar yoga. Together they described hundreds more asanas, revived the popularity of yoga, and brought it to the Western world. Many more asanas have been devised since Iyengar's 1966 Light on Yoga which described some 200 asanas. Hundreds more were illustrated by Dharma Mittra.

The Yoga Sutras of Patañjali (IAST: Patañjali yoga-sūtra) is a compilation "from a variety of sources" of Sanskrit sutras (aphorisms) on the practice of yoga – 195 sutras (according to Vyāsa and Krishnamacharya) and 196 sutras (according to others, including BKS Iyengar). The Yoga Sutras were compiled in India in the early centuries CE by the sage Patanjali, who collected and organized knowledge about yoga from Samkhya, Buddhism, and older Yoga traditions, and possibly another compiler who may have added the fourth chapter. He may also be the author of the Yogabhashya, a commentary on the Yoga Sutras, traditionally attributed to the legendary Vedic sage Vyasa, but possibly forming a joint work of Patanjali called the Pātañjalayogaśāstra.

The Yoga Sutras draw from three distinct traditions from the 2nd century BCE to the 1st century CE, namely Samkhya, Buddhism traditions, and "various older ascetic and religious strands of speculation." The Yoga Sutras are built on Samkhya notions of purusha and prakriti, and are often seen as complementary to it. It is closely related to Buddhism, incorporating some of its terminology. While there is "an apparent lack of unity and coherence," there is a "straightforward unity to the text," which focuses on "one-pointed awareness" (ekagrata) and "content-free awareness" (nirvikalpa samadhi); the means to acquire these, namely kriya yoga ("action yoga") and ashtanga yoga (eight-limb yoga); the results acquired from the attainment of these levels of awareness; and the final goal of yoga, namely kaivalya and liberation.

Yoga as exercise is a physical activity consisting mainly of postures, often connected by flowing sequences, sometimes accompanied by breathing exercises, and frequently ending with relaxation lying down or meditation. Yoga in this form has become familiar across the world, especially in the US and Europe. It is derived from medieval Haṭha yoga, which made use of similar postures, but it is generally simply called "yoga". Academic research has given yoga as exercise a variety of names, including modern postural yoga and transnational anglophone yoga.

Postures were not central in any of the older traditions of yoga; posture practice was revived in the 1920s by yoga gurus including Yogendra and Kuvalayananda, who emphasised its health benefits. The flowing sequences of Surya Namaskar (Salute to the Sun) were pioneered by the Rajah of Aundh, Bhawanrao Shrinivasrao Pant Pratinidhi, in the 1920s. It and many standing poses used in gymnastics were incorporated into yoga by the yoga teacher Krishnamacharya in Mysore from the 1930s to the 1950s. Several of his students went on to found influential schools of yoga: Pattabhi Jois created Ashtanga Vinyasa Yoga, which in turn led to Power Yoga; B. K. S. Iyengar created Iyengar Yoga, and defined a modern set of yoga postures in his 1966 book Light on Yoga; and Indra Devi taught yoga as exercise to many celebrities in Hollywood. Other major schools founded in the 20th century include Bikram Yoga and Sivananda Yoga. Yoga as exercise spread across America and Europe, and then the rest of the world.

The standing asanas are the yoga poses or asanas with one or both feet on the ground, and the body more or less upright. They are among the most distinctive features of modern yoga as exercise. Until the 20th century there were very few of these, the best example being Vrikshasana, Tree Pose. From the time of Krishnamacharya in Mysore, many standing poses have been created. Two major sources of these asanas have been identified: the exercise sequence Surya Namaskar (the salute to the sun); and the gymnastics widely practised in India at the time, based on the prevailing physical culture.

The origin of standing asanas has been controversial since Mark Singleton argued in 2010 that some forms of modern yoga represent a radical reworking of hatha yoga, in particular by adding standing asanas and transitions (vinyasas) between them, and by suppressing most non-postural aspects of yoga, rather than a smooth continuation of ancient traditions. These changes enabled yoga to be practised as a flowing sequence of movements rather than as static poses, and in turn this allowed sessions to focus on aerobic exercise.

K. Pattabhi Jois (26 July 1915 – 18 May 2009) was an Indian yoga guru who developed and popularized the flowing style of yoga as exercise known as Ashtanga (vinyasa) yoga. In 1948, Jois established the Ashtanga Yoga Research Institute in Mysore, India. Pattabhi Jois is one of a short list of Indians instrumental in establishing modern yoga as exercise in the 20th century, along with B. K. S. Iyengar, another pupil of Krishnamacharya in Mysore. Jois sexually abused some of his yoga students by touching inappropriately during adjustments. Sharath Jois has publicly apologised for his grandfather's "improper adjustments".