There is a common misconception of What Fa jing is. True Fa Jing is using natural body mechanics, relaxation, mind intention (a killing intention), and the intrinsic energy to attack someone internally. There is a misconception that using those principles to push someone 8 feet away is Fa Jing, that is pushing energy, and your using the person's own imbalance of weight or force to do it, even if its subtle. Fa Jing should penetrate their physical body and cause damage internally, although many martial art styles use this principle and convert it to physical energy (so they tense their fist or muscles when it lands etc.) and shock the physical structure, causing massive physical damage, such as a break etc. But this is NOT the same as Fa jing, usually if someone were hit by true Fa Jing, it would cause damage internally, disrupt their flow of blood or chi in accordance to where he was hit. This can also be used for healing. In Kung Fu, internal damage can be caused by using internal principles to develop physical power, and you attack points as specific angles etc. to get the deadly effect. Yet Fa Jing is completely relaxed, and everything happens naturally, including the tensing of the fist. When someone begins to attack, before their attack finishes your Fa Jing strikes whereever there is an opening. And because of the closing effect of Fa Jing, directly after your attack makes contact with your opponent your next Fa Jing strike should already be on its way. Therefore it uses almost no physical strength (although you can combine it external strength, ala MANY kung fu methods) and since the recyclcing process is done constantly, it can be done over and over. That is why Taiji used to be taught LONG before they ever taught one how to use fa jing energy, because without overcoming the mind and learning how to relax everything, even in tense situations, and as well as your body moving as natural as possible, the Fa Jing would not be "pure." Also because after every yang technique there is always a transition move which then recycles the energy and brings it back, some say that you actually drain your opponent after the immediate relaxation of a fa jing strike, while it is possible it is not necessary. Without this kind of training students could actually harm themselves with improper fa jing training, and without knowing how to balance yourself out and recycle your energy, then you are exerting too much force and is actually bad for your health. When your young you could do it more often, but as you get older this is crucial.