Yang style tai chi is the most popular of the major tai chi branches. Traditional Yang style was founded by Yang Lu’Chan in the early 19th century and came into prominence when he was engaged by the Chinese Imperial Family to teach the Imperial Guard. It subsequently branched off into Wu style (which features smaller movements and upright stances) and Cheng Man-ch’ing’s relaxed derivation. Whilst these are both closely related to the original Yang style they are seen as distinct branches in their own right.
In the 1950s the Chinese National Physical Culture and Sports Commission instructed four tai chi masters, Chu Guiting, Cai Longyun, Fu Zhongwen, and Zhang Yu, to create a simplified style of tai chi as an exercise for the people. They came up with a Yang style form which condensed the longer forms into just 24 movements whilst trying to maintain the traditional flavor and benefits. This is now the most popular tai chi form in the World and is sometimes referred to as modern Yang Style.
I practice traditional Yang style which includes a slightly older rendition of the form developed by Yang Chengfu which he subsequently modified. This was passed down to Ip Tai Tak and John Ding. My teacher Philip Kubilius was a student of John Ding, a teacher at his academy and took private lessons with him.
With traditional Yang style the form itself is just part of the training, other aspects including zhan zhuang or standing meditation, neigung exercises and push hands. There is also a strong emphasis on usage of the mind which manifests itself with many subtleties in the postures.
Over time practitioners experience a number of physiological and psychological changes, often becoming much calmer, more patient, more agile physically stronger. It appears that the agility and increase in strength is derived from using core muscles, aligning the bones and a development of the nervous system, though further research is required for us to understand the entire process in Western terms. The traditional Eastern paradigm describes the development process in terms of chi (internal energy), and this can certainly be a useful model.