Linear Motion (Hip Rotation)
Hip rotation helps achieve maximum power in any technique, whether it be using punches, kicks, or blocks. It is used in combination with other body movements to complete a technique. As stated above in the equation F = ma, force is increased by increasing mass or acceleration. The fist has a small mass, but, by linking it to the mass of the entire body, the striking force of the fist increases. Techniques that only use arm or leg muscles for power do not draw on the power of the other muscles of the body or the mass of the body. Using other muscles to drive hip rotation and then using the rotation to add power to a technique insures the technique will carry the maximum power the body can generate. Hip rotation also increases the speed of a technique.
Hip rotation is based on two principles:
- Summation of forces. Hip rotation reinforces the transfer of mass to into the technique. To properly use the summation of forces in a technique, the movement must be started by the larger, stronger, generally slower, muscles of the body (the hips and thighs) so they will be moving into the target along with the quicker hands or feet together at the moment of impact.
- Stretch reflex.In the stretch reflex, a muscle is stretched immediately before it is contracted so it will contract more forcefully than if it had not been stretched. If the hips start moving first, the lagging leg will be stretched before it moves into the kick.The lower back should have a slight, normal curve. Some women's buttocks protrude further than most males so some instructors try to make these women tuck their hips up further than normal so that their profile looks similar to a male profile. This flattening of the lower back should not be done.