Sool-Ki are the core techniques of Hapkido, called "Hap Ki Sool" when the training object is self defense to keep oneself intact.
In Hap Ki Sool, the principles of the circle, direction, and angle are used, along with the physical principles of harmony, circle, and flow. Similarly, the human bodies vital points, pressure points, and joints are utilized in order to control an opponent, while also controlling the opponent's breathing. By way of a "sending power" an opponents inner situation and breathing are controlled.
Also, a training person makes a strong body with harmony of muscle, bone, energy, pressure points, and strong spirit power with life and death in mind as the essence of martial art.
Sool-Ki is divided into two kinds: one is "bare hand technique" and the other is "weapon technique" by tools.
• Do Soo Sool (bare hand technique) ; Bare hand techniques are divided into: "Kwan-jeol-ki(joint using technique)", "Hyeol-do-ki(pressure point using break technique)", "Dang-sin-ki(pressure point using strike and kick technique)", "Jeon-hwan-ki(step using technique)", "Cheo-sool-ki(throwing and push down technique)".
There are detail that Kwan-jeol-ki divided nature flow direction joint using technique and reverse flow direction joint using technique, Hyeol-do-ki and Dang-sin-ki divide 14 meridian line, Jeon-hwan-ki divides into inside turning and outside turning, Che-sool-ki is divided into throwing and push down technique.