To break four or more boards, the kicks must have a devastating striking force. Devastating striking forces come from two sources: hip rotation and hip rollover, both of which add a slight thrusting motion to the kick. It is as if, just before impart, an additional two powerful forces are suddenly added to the striking force of the kick. When standing on the floor, hip rotation comes from the rotation of the support foot. As the support foot rotates, the hip rotates into the kicking leg, adding the mass of the entire body to the kick. The rotating foot, and its accompanying hip rotation, should occur in a snapping motion at the end of the kick so all the forces are applied to the kicking foot simultaneously at the moment of impact. In a jump kick, adding hip rotation is more difficult since both feet are off the floor.
Hip rollover occurs when the hips rotate over the horizontal axis of the kick. As the kicking leg extends, the hip snap rolls over the horizontal plane of the leg to use the massive hip muscles to snap the mass of the lower body into the kick.
These two hip movements, the rotation and the rollover, are what separate a devastating kick from a perfectly performed kick, or a high, flashy kick. The two hip movements add tremendous striking force to the kick at the moment of impact. These forces will only be present for a split second and will only occur over a couple of inches, so accuracy and focus are very important. Just before or just after impact, these forces will diminish quickly and the kick will revert to its normal power, still powerful, but not devastating.