Taiji is a form of Chinese martial art, and is not just a form of exercise like aerobics. It is, however, very different from many other types of martial arts, such as Karate, Taikwando, Judo, Shaolin Kung-fu, Boxing. It's power is not generated from muscle strength, but rather it's based on internal joint alignment, rotation to create various speed, length, width, angle, leverage against the opponent. It is generally perceived to be slow, but in reality, that is just one way that it is practiced, so that one can focus on training the precise body alignment. In application, it is most definitely fast.
The widely known health benefits of Taiji are really just by-products, while the main purpose of Taiji is for combat. Any exercise that one performs every day will bring health benefits like better blood circulation and faster metabolism.
Taiji training is not about breaking wood boards or bricks, it is about efficiently beating the opponent, and defending oneself.
If you are interested in finding out more about Taiji, go to http://practicalmethod.com.