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The issue of simple rapid 180 degree turns executed during normal back and forth kihon practice is discussed on the web page titled:
Limitations of such simple turns are that they allow the karateka to deal with opponents within only a 180 degree range and there is no lateral motion of the body center of momentum as may be required to avoid an energetic attack.
This web page focuses on general aspects of execution of rapid turns about one leg that involve a combination of a large amount of kinetic energy, an initial lateral center of momentum shift, an arbitrary angle of rotation and a final lateral center of momentum shift. The first lateral center of momentum shift allows the karateka to avoid a committed high energy attack. The second lateral center of momentum shift is used to enable delivey of kinetic energy to the opponent.
If you ask a karate-ka to turn on the spot as fast as he can, most karate-ka will initially attempt an instinctive turn using one leg as the pivot axis and the other leg for propulsion to revolve around the pivot axis. By so doing he/she will achieve a turn rate of about 1 revolution per 2 seconds, or 0.5 revolutions / second. Given a moment to think about it, he/she will do a jump turn as in the kata Enpi and increase his/her turn rate to about 1.5 rotations / second. The reason why the jump turn in Enpi is much faster is that its moment of inertia I, where:
I = sum over all i of Mi Ri^2
with respect to the vertical pivot axis is minimal.
An engineered turn is a turn that instead of being instinctive is carefully designed to achieve maximum turn rate. A top Olympic male figure skater can execute a quad which consists of a vertical jump of about 0.5 metres during which his body rotates four times in the air. A simple calculation using the known acceleration of gravity of 9.8 m/s^2 shows that the skater is in the air for about 2/3 second and that his average turn rate is 6 rotations per second. However, top Olympic male figure skaters are exceptional athletes. A more realistic turn rate for most karate-ka doing Fisher Shotokan is half the top Olympic rate or 3 rotations per second. At that turn rate the 270 degree turn in Heian Shodan can be executed in 0.25 seconds, which meets the time limit of Fisher Shotokan.
FISHER SHOTOKAN TURN OVERVIEW:
At the start of a Fisher Shotokan turn both feet are on the floor and the legs and hips acting together exert a twisting action which applies positive torque to the upper body. As a result positive angular momentum flows from the ground into the upper body. As soon as one foot is no longer in firm contact with the floor part of the positive angular momentum in the upper body flows back down into the hips and legs, enabling their rotation.
As angular momentum is redistributed through the body the rotation rate of the upper body slows down and the rotation rate of the lower legs increases so that the lower legs can catch up to the upper body.
During the free rotation there is angular velocity and kinetic energy gain by forcing the body, arms and legs toward the vertical axis of rotation.
If there is no energy discharge, when the unloaded foot again touches the floor the unloaded foot will stop revolving around the pivot axis and will exert reverse (negative) torque on the upper body to stop it rotating. This reverse (negative) torque causes positive angular momentum to flow out of the body and into the ground. Angular momentum has a sign as well as a magnitude. If the unloaded foot could continue to apply this reverse (negative) torque the angular momentum remaining in the body would eventually become negative, causing the body to rotate in the opposite direction.
An initial 50%/50% weight distribution stores energy in the legs that together with proper side to side leg spacing provides the initial torque impulse, simultaneous to the initial hip spin, that maximizes the angular momentum at the start of a turn. This high angular momentum enables a turn rate that is much higher than the corresponding turn rate that is possible with the initial 70%/30% weight distribution of an unloaded front stance. Note that a loaded front stance has about a 50%/50% weight distribution.
Note that to generate torque about the spine axis the legs must work together to provide equal but opposite displaced horizontal force vector components. With a 70%/30% weight distribution the horizontal force vector components are much less than with a 50%/50% weight distribution. The horizontal force vector components and the torque go to zero when one foot is not on the floor.
TURNS ABOUT ONE LEG:
A Fisher Shotokan turn about one leg commences with an initial explosive movement that is used to develop angular momentum about a selected pivot point. After commencement of free rotation there is a moment of inertia reduction that increases both angular velocity and kinetic energy. Most of the moment of inertia reduction is achieved by pulling both the unloaded leg and the spine axis toward the vertical pivot axis. Further moment of inertia reduction is achieved via complementary arm action. When the turn is complete the accumulated kinetic energy is available for delivery to the target.
Fisher Shotokan novices should execute turns of < 90 degrees pivoting on the ball of the supporting foot and should execute turns of > 180 degrees pivoting on the heel of the supporting foot. Advanced students can shift their weight during a turn and pivot on the ball, center or the heel of the supporting foot as required to adjust the distance from their opponent.
Sensei Fisher has identified that it is critical to have correct leg spacing, both front to back and sise to side. Initially there should be a 50%-50% weight distribution with the back hip hoint slightly in front of the big toe of the back leg, with that big toe pointed no more than 45 degrees away from the opponent.
Sensei Fisher points out that if the legs are too close together side to side it is impossible to exert sufficient torque to execute a fast turn. A very narrow side to side leg spacing telegraphs incapability of executing a fast turn.
Sensei Fisher has identified that having the upper and lower parts of the body unified with a vertical spine is crucial to successful execution of any fast turn. During the turn the centers of momentum of the pelvis, trunk and head must remain in a straight vertical line referred to herein as the spine axis. If this condition is not met the rotation is unstable and the moment of inertia is too large to permit a fast turn. Sensei Fisher reminds us that to preserve the option of a fast turn in kumite one must always be body upright with the nek vertical and the ass and the chin tucked in.
Turns in Fisher Shotokan are executed using hip a spinning technique. Using this technique a turn rate of 3 rotations per second, or (1/3) second per rotation is readily achieveable by a physically fit karateka. The time interval required for a (3/4) rotation (270 degree) turn is:
(3/4)(1/3) second = (1/4) second.
In addition to the spinning time interval each turn has associated with it a short time interval for accumulation of angular momentum and a short time interval for energy discharge. If each of these time intervals is (1/8) second, the total elapsed time for the technique is (1 / 2) second. This is about the length of time that a karate-ka has to respond to a serious attack.
DYNAMIC ACTION SEQUENCE OF FISHER SHOTOKAN TURNS:
A turn is like any other Fisher Shotokan technique. It consists of a loading and an unloading phase. These phases are seamless and executed in one continuous motion. The position at the transition between the loading and unloading phases is known as the Mid-Point Fully Loaded Position (MPFLP).
The laws of physics require that the following elements be embedded in all Fisher Shotokan turns. These elements must be executed continuously in the correct sequence within a total time of less than 0.5 seconds. Note that some elements are executed simultaneously. It is helpful when communicating Fisher Shotokan skills to be able to identify the individual elements of each turn. However, in execution all the elements of the turn must be performed. The elements cannot be effectively performed in isolation.
1. If the leg muscles are not already loaded at the commencement of a turn they must be loaded using a vertical Center of Momentum (CM) drop so that the legs can provide the required initial burst of energy and torque.
2. In Fisher Shotokan, due to the human skeleton design, all turns are backward. A turn pivoting on the right leg is Counter Clock Wise (CCW). A turn pivoting on the left leg is clockwise (CW). The choice of a CW turn versus a CCW turn is in part determined by the desired direction of lateral body center of momentum motion.
3. A Fisher Shotokan turn starts with a rapid horizontal movement of the body Center of Momentum (CM) to a point on the desired vertical pivot axis. The linear force, from the leg muscles, has a vector that is slightly displaced from the body Center of Momentum. During this movement both feet are in firm contact with the ground. The leg force in combination with the horizontal displacement of the force vector from the pivot axis causes torque and hence angular momentum about the pivot axis.
4. For turns < 90 degrees the pivot point is usually the ball of the supporting foot. For turns > 180 degrees the pivot point is usually the heel of the supporting foot. However, the pivot point can be shifted if it is necessary to gain additional distance from the opponent.
5. The initial hip spin causes vigorous hip rotation about the vertical pivot axis which accumulates upper body angular momentum due to torque transmitted through the legs while both feet are in firm contact with the ground. The related kinetic energy is generated by the leg and hip muscles.
6. Simultaneous vigorous shoulder rotation about the vertical pivot axis with arms leading the body while both feet are in firm contact with the ground causes further upper body angular momentum due to torque transmitted through the legs and hips. The related kinetic energy is generated by the shoulder muscles, not the hip muscles.
7. Ankle movement that positions the foot of the loaded leg to allow free rotation about the pivot point. The pivoting leg is fully loaded with the downward force vertically concentrated at the pivot point. If the heel is the pivot point the pivoting foot must be positioned to prevent the ball of the foot or the toes dragging during rotation. The pivoting foot should revolve around the heel. The other foot lifts clear of the ground and is drawn toward the vertical pivot axis to enable free rotation.
8. After free rotation commences the higher angular velocity of the arms provides excess angular momentum which is used to exert torque to accelerate angular acceleration of the remainder of the body. This torque slows the revolution of the arms around the vertical pivot axis and assists in positioning the arms in the upper body Mid-Point Fully Loaded Position (MPFLP) with respect to the trunk.
9. Vigorous contraction of buttock muscles retracts the extended unloaded leg until it's Achilles tendon bounces off the shin of the loaded leg and moves the spine axis to the vertical pivot axis. Simultaneous retraction of the extended arms to the upper body MPFLP at the body trunk increases rotational kinetic energy. The spine axis must remain vertical. These actions collectively reduce the moment of inertia about the vertical pivot axis and hence increase both the angular velocity and the total rotational kinetic energy. These actions must be complete within half of the turn angle to achieve the desired average turn rate and to ensure that the opponent does not deflect the counter attack. If the arms fail to reach the upper body MPFLP the upper body will not be fully loaded in time for the unloading phase of the technique, which begins from the bottom up
10. On 90 degree turns it is very important to not give the arms too much excess angular momentum with respect to the trunk or the arms will not be able to return to the upper body MPFLP in time for the following block/strike. Too much angular momentum in the arms will throw the upper body out of synchronization with the lower body.
11. Wait until the desired angle of rotation is achieved. The big toe of the pivot (loaded) leg should point radially toward the opponent. If the front hand is to be used during the unloading phase of the turn, as practiced in most katas, the hips and shoulders should be square to the target at the instant of energy delivery. The arms should return to the upper body MPFLP in preparation for the next movement.
Flattening of the pivot foot can be used to cause drag to slow rotation when the desired angle is reached;
12. Block to deflect the incoming attack in the direction opposite to the lateral body center of momentum movement caused by the turn. Simultaneously reverse punch the opponent with the retracted hand.
13. Press the heel of the pivot (loaded) leg into the ground and drive (half step) out toward the target with the unloaded leg which: increases the moment of inertia, lowers the angular velocity and positions the body for delivery of maximum energy to the target. Energy comes from unloading potential energy from the fully loaded supporting leg and from conversion of rotational kinetic energy into radial kinetic energy. The extended foot does not yet touch the ground.
14. Strike/block chudan or gedan with the same hand as the unloaded leg.
15. Momentarily tighten all major muscle groups to make the body rigid at the instant of impact in order to achieve maximum energy transfer to the target. The extended foot should barely touch the ground.
16. Use the extended foot as a rotation brake to absorb the remaining angular momentum.
17. The extended foot can be planted and used as a focrum to achieve either a long reverse punch or a lunge punch.
RAPID TURNS ON KUMITE MATS:
Many karate kata competitions take place on high friction factor foam rubber mats that were originally designed for kumite (sparing). These mats are usually assembled in one metre square sections that are joined to each other via press fit dovetail joints. The combination of the high friction factor and these dovetail joints make it is dangerous for a karate competitor to execute rapid large angle turns such as are possible in Fisher Shotokan. If the competitor's foot cannot freely rotate while his/her leg is rapidly rotating an injury can easily result. This matter should be addressed by parties that organize karate tournaments. Generally the best solution is to use an unmatted ring for kata. Absent this solution a competitor who is proficient in Fisher Shotokan must slow down his/her turns for safety.
This web page last updated March 20, 2015.
|Contents||Blogs||Introduction||Fisher One Page||Contacts||Links|