Tập yoga (tiếng Anh: 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". Academics have given yoga as exercise a variety of names, including modern postural yoga and transnational anglophone yoga. Posture is described in the Yoga Sutras II.29 as the third of the eight limbs, the ashtanga, of yoga. Sutra II.46 defines it as that which is steady and comfortable, but no further elaboration or list of postures is given. 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. Haṭha yoga's non-postural practices such as its purifications are much reduced or absent in yoga as exercise. The term "hatha yoga" is also in use with a different meaning, a gentle unbranded yoga practice, independent of the major schools, often mainly for women. Practices vary from wholly secular, for exercise and relaxation, through to undoubtedly spiritual, whether in traditions like Sivananda Yoga or in personal rituals. Yoga as exercise's relationship to Hinduism is complex and contested; some Christians have rejected it on the grounds that it is covertly Hindu, while the "Take Back Yoga" campaign insisted that it was necessarily connected to Hinduism. Scholars have identified multiple trends in the changing nature of yoga since the end of the 19th century. Yoga as exercise has developed into a worldwide multi-billion dollar business, involving classes, certification of teachers, clothing such as yoga pants, books, videos, equipment including yoga mats, and holidays.