Chen Taijiquan requires not only sturdiness and gentleness but also fastness and slowness because changes of the negative and the positive energy (Yin and Yang) can not be limited.
In other words, only practicing slowness is just one of the classical disciplines of Taijiquan and fastness training can help practitioners understand the changes of Yin and Yang. In order to develop internal and external power, it is required to practice "Fast forms" as known as Paochui (Cannon Fist.)
Silk Reeling exercises will help you understand Chen Taijiquan's mechanisms and develop your energy.
Here are certain rules that we have to keep during Taijiquan training in "Preparation."