difficult to learn. He thus created a shortened 37-movement version that he taught in his schools. Zheng's form became the dominant form in the eastern United States until other teachers immigrated in larger numbers in the 1990s. He taught until his death in 1975. United Kingdom Norwegian Pytt Geddes was the first European to teach tai chi in Britain, holding classes at The Place in London in the early 1960s. She had first encountered tai chi in Shanghai in 1948, and studied with Choy Hok Pang and his son Choy Kam Man (who both also taught in the United States) while living in Hong Kong in the late 1950s. Lineage Modern forms The Cheng Man-ch'ing (Zheng Manqing) and Chinese Sports Commission short forms are derived from Yang family forms, but neither is recognized as Yang family tai chi by standard-bearing Yang family teachers. The Chen, Yang, and Wu families promote their own shortened demonstration forms for competitive purposes. Purposes The primary purposes of tai chi are health, sport/self-defense and aesthetics. Practitioners mostly interested in tai chi's health benefits diverged from those who emphasize self-defense, and also those who attracted by its aesthetic appeal (wushu). More traditional practitioners hold that the two aspects of health and martial arts make up the art's yin and yang. The "family" schools present their teachings in a martial art context, whatever the intention of their students. Health Tai chi's health training concentrates on relieving stress on the body and mind. In the 21st century, Tai chi classes that purely emphasize health are popular in hospitals, clinics, community centers and senior centers. Tai chi's low-stress training method for seniors has become better known. Clinical studies exploring Tai chi's effect on specific diseases and health conditions exist, though there are not sufficient studies with consistent approaches to generate a comprehensive conclusion. Tai chi has been promoted for treating various ailments, and is supported by the Parkinson's Foundation and Diabetes Australia, among others. However, medical evidence of effectiveness is lacking and research has been undertaken to address this. A 2017 systematic review found that it decreased falls in older people. Sport and self-defense As a martial art, tai chi emphasizes defense over attack and replies to hard with soft. The ability to use tai chi as a form of combat is the test of a student's understanding of the art. This is typically demonstrated via competition with others.