In order to execute effective karate blow, It is necessary to learn basics of human anatomy, physiology and first aid. This knowledge is called – kyusho. Kyusho knowledge was kept as secret for centuries. It includes: positions of vulnerable points, use of proper impact tool and situation which is the best for applying technique to some point.
If we compare karate technique with arrow, then kyusho is poison on that arrow. Master Funakoshi tells that “quick and extremely accurate blows, that never miss the vital point, are the essence of real karate”.
There are 3 ways to traumatize vital points: (1) strike or punch, (2) poke or press and (3) grab or pinch. As result, several conditions may occur: pain, shock, respiratory disturbances, temporally paralyze, hyper torsion, joint dislocation, bone fracture and internal bleeding.
This is not systematized knowledge, but rather empirical, usually transmitted orally to top students only. Only ancient written source on this topic is Okinawan manuscript called Bubishi.