Open hand forms according to the Tai Chi Classics condition the muscles and tendons.
Most people are only accustomed to seeing these forms done slowly, but there are also fast forms of Tai Chi Chuan.
The doing the forms slowly is where everyone should begin. This is because of the complex nature of the movements in Tai Chi. Slow form training teaches "sung" or "using the least possible effort" a concept that is usually not a major part of the curriculum of hard style martial arts in the beginning stages.
It also allows the student to develop the circular pattern of movement and close to the body hand position found in good Tai Chi.
Fast form training closer resembles hard style martial arts but is more compact. While “fajin” strikes appear to be longer than even some hard style movements it is a momentary period and usually ends with the practitioner once again in a stance that is loose and relaxed.