(reproduced from http://shaolin.org/video-clips-11/uk-summer-camp-2015/fa-jing.html)
Fa-jing means exploding force. There are two fundamental requirements:
The exponent must have sufficient internal force to explode
He must have the right mechanics
An effective way to develop internal force is zhan zhuang or stance training.
Past masters have provided an excellent way for exploding force, namely to start from the back leg, rotate the waist, and complete at the hand.