“Gaseous Expansion is the concept of ‘filling the volume’ of the defensive situation at hand.” (Quoted from Advanced American Kenpo Concepts article on Gaseous Expansion)
It is the natural adaptations to the chain of events that occur once a defensive situation begins. By altering small aspects of your technique, you can adapt your reaction to the opponent’s reaction. You flow into the cavities of their reactions and counter-reactions to control them to your end goal. In our case, the end goal is immobilization, submission or destruction.
Your expanded awareness of the environment is just as important as understanding the biomechnical cause and effect of your techniques. In short, the gaseous expansion investigation is exploring many of the “what if”s of a confrontation. Having only read their explanation of the concept, I can not replicate their actual drills or methods for exploration. It would be best to seek out a seminar on American Kenpo Karate theories and application to learn more about this concept.
How does it adapt to our art? When we first learn a technique, it is done slowly, step by step. Then it evolves into a smoother version. Then the strikes and levers begin to make sense, making it run smoother on various body types. Then the uke moves “unconventionally” and we adapt. Then we expand the situation to engage and conquer, where we complete the technique by immobilization, submission or destruction — not just getting away. It is at this point that we investigate and flow further using “gaseous expansion”.