The Historical Norm....
Of any Martial Art s to manipulate or strike the opponents body to; damage, control or dominate.
But almost all styles work and train to accomplish this from the outside of the body at the body's maximum strength and resilience. The exterior body is a miraculous adaptive and protective suit that monitors and perceives threat or change in order to adapt the internal body to cope with the influence (good or bad).
The layers have this duality as do the internal structures, but to access the more influential and weaker internal structures we must first learn to get past, overwhelm or influence the outer protective systems. The further inside you can influence the body as compared to manipulating the exterior, the more readily and profoundly you will control or overwhelm the entire being.
So many people spend so many hours training to fight the opponents last movements, that being the physical exterior actions and movements. So few spend time stopping them at the source before it is converted into speed, power and agility of the exterior body. This favors the better athlete and leaves little hope for the common man... it is also the most inefficient and difficult to manage or manipulate.
