Fa jin, fajin or fa chin (fājìn, 發勁), sometimes misspelled as fajing, is a term used in some Chinese martial arts, particularly the neijia (internal) martial arts, such as xingyiquan, t'ai chi ch'uan (taijiquan), baguazhang, bak mei and bajiquan.
It means to issue or discharge power explosively or refining the explosive power, and is not specific to any particular striking method. With this definition in mind, a boxer is also capable of the same. However, in the context of internal martial arts, this process commonly seen as a set of methods capable of generating the energy further refined and focused through many more muscle groups (particularly in the waist and torso - the dantian) allowing feats with far less visual physical expression such as the one-inch punch. Jìn (勁), or "power", is often confused by Westerners with the related concept of jīng (精), which literally means "essence." To generate the fa jin, according to the traditional explanation, it is necessary to transfer qi from dantian towards the limb or body part (e.g. shoulder, head, hip) that will perform the technique with explosive force (bàofālì 爆發力). In terms of physics, it is a simple matter of body alignment and torque.
Jin describes the ability to generate force. If a person is off balance, they have no jin. Jin and qi are inherently combined concepts in internal martial arts. The way it is explained is that the qi cannot penetrate the muscle to produce force. From a biomechanics perspective, the person starts in a weak physical state, which is then quickly acclerated like a "whip" in a coordinated movement of the entire body along with a shift in body weight to generate explosive power. The idea behind the technique is not exclusive to traditional Eastern martial arts, a similar idea can be found within boxing in the falling step.
Taijiquan and fa jin
In the practice of taijiquan it is a description of a technique, generally indicating a sudden release of energy obtained by the coordinated movement of the entire body. Every technique can express fa jin, not just kicks, punches, elbows and knees, but also holds, levers and projections. Essential is the mastery of the techniques of chan ssu jin silk reeling. The fa jin released during exhalation is almost unconscious. This technique is referred to in the forms of training school as the Lao Jia Chen Paochui (old frame, cannon fist, one of the two original forms Chen-style t'ai chi ch'uan), while in Yang school, especially for those who have a direct lineage to Yang Shaohou the fa jin is added to techniques to release the stored energy.
According to many sources, fa jin does not just refer to the power generation method but also the capability of such an attack to penetrate the body causing more internal damage through a process described as similar to a "shockwave". Traditional masters explain it as flooding the opponents body with qi. From a physics perspective, a explanation is that the strike transfers your body's momentum over a shorter period of time, leading to increased impulse. This is usually accomplished using a snappy attack (visually similar to a jab) that is stopped as quickly as possible at an optimum predetermined point just beyond the target. However, while a jab has increased impulse, it has minimal momentum when compared to a punch with follow through, so overall force is still far smaller. In comparison, fa jin also focuses on increasing impulse, but proper timing and coordination allows the user to include the power of several large muscle groups as well as their own body weight into the punch. Therefore, the momentum of an attack is increased by a large amount while maintaining high impulse - resulting in increased force.
Fa jin and the dantian
A main principle in creating fajin, is using your dantian. The dantian is thought to be the storehouse of your energy and can be used in striking. One technique described by Master Wang Jianqiao for developing fajin is by breathing into your lower abdomen (dantian) and creating a pressure. When you strike and squeeze your lower abdomen tight so that the core becomes compact, unifying the torso, this actively engages more of the muscle fibers to generate more force.
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