The title says it all

Is

Fa jin means to issue power.

Fa-jin is just a general term or an "umbrella" term. Sometimes various Fa-jin movements from some practitioners will intersect with Kiai from other practitioners, sometimes it won't. Synonomy between two words is often just synonomy in the mind of the lexographer or word user, and does not necessarily depict a sameness of essence.

Kiai: (if you are talking about the Japanese word used in relation to martial arts) Means a burst of energy that coinsides with another action. Ki as in energy, Ai as in accord. Some will tell you kiai and aiki are closely related if not the same thing.

They are the same in the sense that you are using breathing to link your spirit and you body into one action. There are subtle differences.

A kiai is more extroverted and it is used to raise the spirit during practice or in a fight. During practice you use a kiai to raise the spirit of those you are practicing with as well as yourself. In a fight, you can use it to intimidate your opponent. It is not completely extroverted, however, and a kiai can help build your self-confidence.

A FaJing is more introverted and is a more "humble" expression of your energy. You are searching within yourself throughout your body for that energy and unifying it into one blow. It is not as much about expressing yourself to others as a "kiai".

In either case, the quality of the blow depends on the level of the practitioner.

In my opinion they are two different things.

Kiai is psychological more than physical, both in practise and its intended effect.

Fajin on the other hand is a physical skill aimed at reducing the amortization phase of an expression of force – it’s like plyometrics for combatives.

>>"reducing the amortization phase of an expression of force"

Can you elaborate a little more on what you mean by this? It sounds interesting.

I’m not a human movement scientist, so I would recommend looking up sport coaching sources on the Net for a more conclusive definition but according to my understanding, the amortization phase is a term used in Plyometrics to describe the stretch reflex loading of a muscle prior to muscle actions that occur over very brief periods of time i.e. explosive actions – the classic cocking of the fist before throwing a punch.

Basically, the longer the amortization phase, the slower and generally more clumsy the resultant expression of force. It is important to understand that this relates to compound expressions of power rather than localised muscle strength, although greater general localised muscle strength gives the body the required integrity to absorb the strain of explosive actions. This is why you should train hard before you train smart.

Anyway, an example of a compound expression of power is the clap push-up. In a push-up position rapidly lower and explosively push your body into the air, clap your hands whilst the arms are airborne and then drop back into a push-up position (before your face hits the deck) and repeat immediately without tensing up too much or you will inhibit the stretch reflex – the time from where your hands hit the ground until you are airborne again is the amortization phase. I think that a prominent desire to gain control and augment the effect of the stretch reflex (which is a function of the nervous system) is one of the reasons for the training modalities and the emphasis of “Aliveness” in the Internal MA.

Not wanting to stray too far from the thread, it’s my opinion that Fajin in all its permutations is the TCMA expression of Plyometric training which, while it is very physical training aims primarily at improving nervous function where as “Kiai” or what equates to it in TCMA is utilised to stimulate the endocrine system and this is at the heart of the difference between the two.