Once the kicking leg is cocked, the kick starts with the knee. For side thrust kicks, drive the knee toward the target. For round, hook, heel, etc. kicks, pull the knee around and through the technique.
Knee Moves First
When kicking, do not move the foot first. For example, in a side kick, the knee moves vertically first; the foot follows but it moves quicker than the knee. When the foot is in position, the knee pushes the foot directly toward the target. Do not think of the foot moving first and dragging the knee behind; instead, think of the knee moving first and then pushing the foot toward the target. This motion will add power to the kick, minimize telegraphing the attack, get the kick over the top of any counter kick, and confuse the opponent as to whether the kick will be to a low, middle, or high target.
In kicks, just as in hand techniques, power comes from hips. Without the hips, the only the power in a kick comes from the leg and possibility from a spin. Snap rolling the hip over into a kick applies the mass of the entire body into the kick and give it maximum penetrating power. When kicking, most students concentrate on leg power, some remember to chamber, but many forget the hip action.
A snapping hip roll is the primary movement that separates a karate style side snap kick or a Taekwondo side kick from the more powerful Taekwondo side thrust kick. In the side snap kick, the striking foot is held parallel to the floor and the striking surface is entire length of the outer knife-edge of the foot. In the Taekwondo side kick, the striking foot is also parallel to the floor but the striking surface is just the heel area of the knife-edge of the foot. In the Taekwondo side thrust kick, the kicking foot's final position is perpendicular to the floor, heel upward - toes downward, but the striking surface is the same as with the side kick, the heel area of the knife-edge of the foot. To get the foot into this position, the hip must roll over the kicking leg. This rolling motion is snapped so the heel of the kicking foot is thrust forward applying all the forces of the body into the kick. The resulting kick not only thrusts into the target, it strikes the target with a powerful jolt.