How does it work?

Tai Chi tones and relaxes the muscles. The more relaxed and toned the muscles are, the faster you move. Tai Chi trains the central nervous system to be more efficient, enabling the nerves to give strong signals to the muscles to move faster.
Tai Chi gets your whole body movement coordinated. Moving your body as one unit can dramatically increase your speed and power.

Nowadays it is said that if you practice for the health benefits and Qi development only, then you are practising Tai Chi. If you incorporate both the Qi development and martial techniques together then we refer to it as Tai Chi Chuan.