Stability and Center of Gravity( thang bang va trong tam)

詠春拳 - Wing Chun

Stability and Center of Gravity( thang bang va trong tam)

Gửi bàigửi bởi David » Thứ 7 25/09/04 14:52

Stability and Center of Gravity
by Andrew Williams
The realization of a Martial Artist's personal potential is acquired through the combination of highly developed levels of skill and the Martial Artist's natural abilities.

Introduction
The level of competency, with which a martial arts practitioner is able to strike a target with the maximum of his potential power, combined with precision and accuracy, or likewise receive and redirect any incoming force, is largely dependent on his stability and body control immediately before, during and after the act. There is an important relationship between stability and body control, namely, that a decrease in stability results in a greater need of body control to ensure that the execution of a technique is successful. Interestingly, this increase in body control belies the notion that the highest levels of the martial arts are achieved using the concepts of economy of motion or the conservation of energy. In effect, the ability to maintain the requisite level of stability is one of the factors that determines the level of efficiency and skill at which an athlete operates, doing the least to achieve the most is representative of an accomplished Martial Artist. It is therefore important that the Martial Artist, as with any athlete, has at least a fundamental understanding of the means by which stability is maintained in one's particular art or skill efficiently whilst in the processes of giving and receiving impetus.

The three most important factors to consider in a discussion about stability relative to the performance of martial art movements are:


The line of gravity and its' position relative to the area of the base of support.
The stabilizing function of the core musculature and its' ability to generate and transfer the force used in athletic movements.
The alignment of the body's segmented centres of gravity.

The Centre of Gravity & The Line of Gravity
Before we embark on an investigation of the above three factors, it is necessary to have a fundamental grasp of the principles governing the centre of gravity.

The "centre of gravity" is a term we often hear mentioned in martial art phraseology. Its' relevance to stance, mobility, force generation and stability can easily be overlooked or misunderstood. In general terms, the CoG (centre of gravity) can be considered to be the point where the body's weight is concentrated at a particular point in space and time. In fact, your CoG changes as you change position from one point to another. Further, the CoG is the summation and the centre of all the forces and motions concerned with this movement. The understanding of this concept is essentially the solution to nearly every problem in the analysis of correct or incorrect human posture and movement.

Whilst standing upright with the hands by the sides the CoG is located approximately at the height of the 2nd Sacral vertebrae anterior to the sacrum. For a male this means that the height of his CoG is located at about 56% of his height and AT about 55% for a female. If the left arm IS raised, the CoG will move both vertically and toward the left-hand side of the body. As the CoG is raised, the body's musculoskeletal and neurological systems must exert more effort in order to maintain stability.

Combined Centers of Gravity
Under curtain circumstances the CoG, and so the line of gravity (LoG), can exist outside of the body and one should be aware of the particular means by which one can move to make best use of this phenomenon. If your LoG falls outside the base of support, you will become unstable. Stability can be regained or maintained, by either repositioning oneself so the LoG falls within the area of the base of support, or by, however briefly, establishing a new base of support that will encompass the new location of the LoG. This is effectively what happens when a powerful blow lands, a new and in most cases, larger base of support is established.

The principles which govern a single body, its relationship with gravity and the giving and receiving of impetus are equally applied when contact occurs between two combatants. We can say that when two bodies share enough mass, they will share a common or combined CoG. In these situations the body's weight may have to be distributed in a fashion that takes into account the change in the position of the CoG. As every time mass is added to or impetus acts on an object a new CoG is established, with the CoG shifting toward the added mass or impetus. As whenever mass is added to an object (or body), or when impetus is projected toward, given to, or received from an external force, a new CoG is established. The CoG of the body's combined forces will shift toward the additional mass or force, this shift being proportional to the mass to or impetus acting on the object.

Though there is much to be said for the ability to control an opponent's CoG whilst maintaining stability in your own structure, it can occur only if a lack of equilibrium can be affected in the opponent. The reason being, that if all other things are equal, where the sum of all the forces working on and through the bodies equals zero, an equilibrium will be maintained. This means that, all other things being equal, an equilibrium cannot be established if one person has a greater mass, and that the man with greater mass, in all likelihood, will move the smaller man around (a = F/m). Whilst this makes for good theater, it may have little significance in a real confrontation. It is often achieved because the pusher has greater mass (or can generate more mass) than the person being pushed. The control displayed may be seen as evidence of the cultivation of good structure, and this may well be true, if all other things are equal. But if the ability to hit with precision and accuracy is lost at the same time, then it does little more than demonstrate who has the greater mass. It should not be seen as an exhibition of the real fighting abilities of that person, because the body's ability to resist movement is directly proportional to its' mass. It would make more sense to utilize the stability afforded by balance and good structure, to strike a vulnerable target with speed, accuracy and aggression, than attempt to "dominate" one's opponent if the confrontation is real. The ability to shove someone around can not always be seen as evidence of real fighting skill. Nevertheless, if you need to break the structure of your opponent's defense, it is more easily done if his central nervous system is being employed to maintain his balance rather than to hit you. This may require that you attack a limb in such a fashion that the balance of your opponent is affected, rather than simply knock the arm or leg out of the way (1). Likewise your opponent's pelvis, torso or head can be struck to achieve the same result. A loss of balance occurs when the line of gravity moves outside the area of the base of support. This loss in equilibrium causes the body to do much to regain its' balance (equilibrium reaction), and the mechanisms controlling balance are brought into action, most times at the expense of other motor skills. An effective attack on the CoG, then, is one which forces the mechanisms responsible for maintaining equilibrium to employ the musculature to regain balance through body control.

The monitoring and transmission of information concerning the body's position and movement include: the vestibular apparatus (equilibrium receptors of the inner ear), muscle spindles, Golgi tendon organs and the Ruffini endings, mechanoreceptors, and visual orientation. Challenging and stimulating these response mechanisms in practice will enhance the coordinated efforts of the body to resist gravity, whilst also improving the athlete's stability when resisting impetus and applying powerful horizontal force. These exercises need not be taught separate from those used to develop the athlete's multilateral base(2).


The body has many reflex responses, some are more easily stimulated than others and can cause one to act with little or no volition. Both exteroceptors and interoceptors can be stimulated, though the latter are perhaps the easier to excite from a martial perspective. Some reactions exhibit reflex like responses, which are usually the result of repetitive stimulus-response actions, the understanding of which is essential, for without this understanding you can easily be made to act, your reactions manipulated and used against you. This idea is more complex than might at first seem. For example, think carefully of the way that some practitioners seem to be able to manipulate their partners in Chi Sau, suggestion that there may exist a sequence of subtle stimulus response mechanisms used to elicit particular patterns of movement. A skilled Sifu may "fool" his students for years, with nothing more than a complex of patterned behavior, wanting them to believe, for whatever reason, that he is untouchable or has super human skill.

This will be the subject of a future article.
1. The Line of Gravity
The Line of Gravity is a straight line that travels through the body's CoG to the ground and runs parallel with the pull of gravity. The nearer the LoG (Line of Gravity) and the CoG are to the center of the area of the base of support, the greater the stability exhibited in the stance. One needs to have the CoG lowered to a point that aids stability, but not so low as to adversely affect the practitioner's mobility. An efficient fighting posture combines the requirements of giving and receiving impetus and for generating balanced movement in a particular direction. If we consider the likely applications of the techniques of Wing Chun along with its' mobility requirements, it could be suggested that the optimal position in the Wing Chun stance is one that, for the most part, maintains the LoG above the center of the area of its base(1). This means a good tactical stance is one where weight of the body is felt evenly through the lower limbs in a static position, but still allows for considerable variability with the introduction of movement and/or external force, these being dependant on the specific requirements of any given moment in combat. For example, when applying powerful forward impetus, where that impetus meets resistance, more weight may be felt in the rear leg even though the CoG and subsequently the LoG have moved toward the external object.

There are various misunderstandings in evidence about the principles governing the LoG and the role it plays in dynamic footwork. One of these can be found in those practitioners who bear most or all of their weight on their rear leg, for example, whilst in a static position. For it is true that the application of force is enhanced and more quickly applied if the LoG is over the edge of the area of base opposite to that from which the force is to be exerted (2). This is a mechanical principle and means that those who adopt this rear weighted position, where the LoG is located toward the rear of the area of the base of support, are adopting a stance that would be better suited to stepping back rather than forward and/or laterally, than would be the case for those who adopt a mid-weighted position. Couple this with the understanding that the rear-weighted position also undermines the stability necessary to execute a ballistic movement to its fullest potential. Conversely, if you adopt a stance where the line of gravity was located toward the front of the area of the base of support, you would be making a tactical error in real fighting, as your opponent would quickly determine that you are limited to a single direction of efficient movement. For reasons of stability and tactics, the martial artist may be better served adopting what is known as an "undeclared position". Here the LoG gravity is maintained over the center of the area of the base of support, allowing for rapid multidirectional movement and the efficient use of the joint complexes responsible for stabilizing the body.


When the weight is supported entirely by the feet, the area of the base of support is defined by combining the area beneath both feet and the area between the feet. An illustration of how to increase The area of the base of support is that when the distance between the feet is increased, so too is the area of the base of support. Though there is a subsequent increase in stability afforded by the increase in the base of support, there may also be a decrease in mobility if the feet are placed too far apart and a strong lateral force component is introduced. When the angle created in the legs is optimal, stability is increased and mobility requirements can be met.

This is only true as long as sufficient friction exists between the surfaces of the feet and ground.
2. The Core Issue
The core musculature plays a key role in all athletic movement. It has been said that all athletic movement is initiated in, transferred through or controlled by the core musculature. A weak core will result in excessive pelvic movement that will be magnified throughout the body and be manifest in immoderate actions of the legs and/or torso and arms. An inefficient core will adversely affect the speed, strength, accuracy and precision of a given technique.

The core musculature is a complicated musculoskeletal complex and as such cannot be fully appreciated in an article of this size and will be investigated in greater detail in the future. I will also cover training methodologies, which will encompass tilt reaction and equilibrium reaction training.

3. Segmented Centres of Gravity
The interrelationships between the core musculature, the centre of gravity, and the area of the base of support of the stance are important to understand. Once these interrelationships are understood, you will be better able to increase your levels of power development, body control and the coordination between the proximal and distal areas of the body.

The body can be seen to have three major segmented centers of gravity (1). Interestingly, these centers are in approximately the same locations as three important areas of power concentration in Eastern theories on internal energy. They are located at the approximate midpoints of the head, thorax and pelvis. If one of the segmented centres of gravity is not aligned correctly, the amount of muscular effort exerted on that portion of the body will have to be increased in order for the practitioner to maintain stability, making him considerably less able to deal with the internal and external forces working on the body. Consider that much of the musculature that is responsible for maintaining the stability of a body out of alignment can better be used in athletic movement. While a certain amount of muscular involvement exists to maintain a functional alignment (segmented CoG in or near alignment), it in no way interferes with the expression of vigorous movement.

An example of poor alignment can be seen in those practitioners who, whilst in Yee Jee Gim Yeung Ma, align their spine poorly and force their shoulder girdles forward giving the appearance of having "rounded shoulders". Rounded shoulders should not to be confused with structural kyphosis. Nevertheless, unless the practitioner is careful, one can beget the other. Given the effect rounded shoulders have on the position of the shoulder complex, it would also be apparent that there is a loss of some mechanical advantage(2). This occurs because the shoulder girdle is abducted and laterally tilted, shortening the pectoralis minor (3) and serratus anterior, with the rhomboids and mid trapezius becoming elongated. The pectoralis major can no longer exert its usual tension on the ribs and the chest becomes depressed. When the sternocleidomastiod, and pectoral muscles lose their lifting effect on the ribs, the diaphragm is in turn lowered, which reduces its' range of motion in respiration. Because those muscles responsible for driving the arm forward of the chest cannot exert their best line of pull, the kyphotic like position can give rise to excessive rotation of the pelvis and torso in an effort to generate power. The head forward, round-shouldered, posture requires many compensatory adjustments to take place in the body. This often results in another segmented center of gravity being employed to counter balance the head's position, lest the person falls forward. Representative of this, and most often seen in Wing Chun practitioners, is in an immoderate posterior pelvic tilt. Here some practitioners have the pelvis tucked in "too far" causing "lumbar kyphosis" or "flat back"(4). Not only can this create an inefficient mechanical structure, it can also be an unhealthy one, particularly when one considers the amount of time some people spend in the Yee Jee Gim Yeung Ma stance. The resultant reduced abdominal tension, which is caused by holding the afore indicated posture, may result in a number of MALAISES, ranging from vertebral problems through to, in extreme cases, visceral ptosis, which can lead to malfunction of the organs in the abdominal cavity. Lumbar kyphosis can also cause or be caused by the shortening of the hamstrings and hip flexors and the lengthening of the iliofemoral ligaments. There is a corresponding reduction in lumber spine mobility, reducing the efficiency of and the rotatory capacity of the thorax, and often means that, in order to produce a powerful movement in a pivoting action, an immoderate rotation in the pelvis needs to occur.


Each body segment has its own CoG when it moves independently, when two or more adjacent segments move together they form a single segment and therefore a new combined CoG.

"Mechanical advantage" measures the relative effectiveness of a lever, in this case the levers found in the shoulder complex.

Aids inhalation and shoulder girdle stabilization, the efficiency of both are reduced in this position.

Excessive posterior tilting (pelvis tucked in) causes the pelvis to lose much of its efficiency as an initiator of movement or where it is required to transmit force produced in the lower extremities, and/or where its' movement is secondary to the spine or lower extremities.
Stability In-built
If you can maintain a "good" posture whilst in your martial stance (particularly when moving), you have stability in-built and your muscular effort can be better used to impart force to your opponent or receive and/or redirect his incoming force.

What then is good posture? Well, in a martial sense, a good posture is one where the forces, which are generated within the body, pass efficiently through the joint axes (kinetic links) and are distributed through optimal skeletal alignment. This then allows for the efficient transfer of force, whether it is the giving or receiving of powerful horizontal impetus. This is best done if sections of the body are inclined in the direction of the incoming or projected force and/or the base of support is lengthened IN LINE with the horizontal force or impetus.

Consider that in fighting (or in practise for it), one must combat the forces of gravity as well as those exerted by an external object, this is true whether one is delivering a blow or working in opposition to an external force. Stance training with an absence of a horizontal force component does little to prepare the athlete for contact. It could be said that a functional static stance is one that exhibits high levels of stability, and is taught with regard given to the eventual actual use of the position established in actual combat (1). This is almost the opposite idea to the many who adopt the Yee Jee Gim Yeung Ma position thinking it an ideal way to bear ones weight for extended periods of time in the practice of forms or techniques. Ideally, though the feet may not move, the muscles of the legs, pelvis and core, which are responsible for stabilizing the body and initiating movement, are innervated sequentially and/or concurrently in accordance with corresponding movements of the torso and upper limbs. Along with this, subtle changes in the position of the CoG should be felt in concert with changes in where the weight is felt on the SOLES of the feet. This way, neurological pathways linking the arms with the legs are developed and refined, and the early establishment of the beginner student's perceptual-motor foundations can begin.


This idea will be covered in greater detail in a future article dealing with the development of the core musculature and further in "Static Stance Training for Dynamic Movement."
Stability while Mobile
When stepping forward (in Wing Chun) the rear foot is characteristic of a particular phase in walking and, in some instances, running. The efficiency of Wing Chun footwork is often dependent on the stride length of our normal gait and the foot's "line of progression". For instance, if the rear foot is too far angled away from our intended line of travel, one cannot make use of the kinetic capabilities of the foot. The foot in this position also affects the stability of the hip complex and its' ability to transfer and generate force. It could and usually does promote hip rotation in the direction that the rear foot is pointing (the foot's line of progression and the "action line") and cause the same side hip to drop, which in turn encourages "hip hike" in the other hip. Hip hike/drop encourages pelvic lateral rotation, thus further affecting the CoG. The resultant stepping action then exhibits a lack of fluid linear progression, this makes for punching and deflecting actions which are stilted and lack the penetrative qualities associated with punches delivered from a stable base of support.

In most cases, when the YJGYM stance is adopted, the hip joints (where the femur inserts into the pelvis) are medially rotated (the feet & knees turned in). From this position it is not too difficult to establish points of balance, stability and postural references. Nevertheless the stability practiced for and the postural references gained in said stance-training are most often lost when stepping commences, because the patterns of movement, particularly in relation to the femur's position in the stance, are no longer in evidence, diminishing the functional crossover of the training effect. An extreme example of this occurs when the knees are pinched together in the Yee Jee Gim Yeung Ma stance, there is also an injury worry associated with this practice(1), as well as a lack of carry over training effect.

The muscles controlling the movement of the hip joint represent some of the most powerful available for force production and so make for one of the most powerful kinetic links in the body. Nevertheless, for this link to function efficiently, it needs to be stabilized, AS there is a direct relationship between the stability of a joint and its' ability to generate force. If the femur is laterally rotated too far, its efficiency in driving the body forward whilst maintaining stability is reduced. If the efficiency of the hip joint is reduced the whole system of kinetic links is affected. One such effect would be to diminish the potential rate of force development of the leg muscles in the drive phase of the step. Other complexes affected include the foot-ankle, knee, hip, vertebral, thorax and chest, and shoulder (and, in some cases, the elbow and wrist complexes). All force originates in, is transferred through or controlled by the core musculature, which has its efficiency diminished by an unstable and/or poorly positioned pelvis, the repercussions of which would likewise be manifest through the rest of the body. This may explain why a punching action perfected in the YJGYM stance may be difficult to duplicate whilst mobile and vice versa (2).

Stepping practise alone, because of the limited ranges of motion involved, will not allow the student to develop his locomotive process to their fullest potential. Stepping should be trained so it becomes a reflex like action (much the same as walking and running); if too much attention is paid to the stepping action, tension will likely develop. It may be best to work on the musculature that affects the mechanics of footwork to ensure a fluid powerful gait is established. This can be done through the practice of particular drills and exercises, some of which resemble established drills performed by speed athletes such as sprinters. Other exercises challenge the balance centers while at the same time aiming to improve the gait patterns for athletic movement. Still others can be found "hidden" within the forms, and postures practiced and adopted in Wing Chun training. These drills are designed to enhance the whole locomotive process, however, particular emphasis can be placed on the drive phase (3) of the step (4), The effective training of which will enhance the forces generated throughout the kinetic link system of the body.


Pinching the knees together whilst in Yee Jee Gim Yeung Ma creates tensile forces in medial aspect of the knee and compressive forces lateral aspects of the knee, the mechanical efficiency of the knee complex is reduced. A wide variety of injuries may result from training in this fashion.

A mechanical & anatomical analysis of locomotion will be presented in future articles.

Stepping forward demands that the muscle groups recruited are quite different in their patterns of innervation than those for jumping. Care must be taken to ensure that time is spent wisely and that the prescription of exercises enables best use of time with regard to the functional crossover of the training effect gained.

Keep in mind that the arms serve a very different purpose in the martial arts than they do in running or walking.
Summary
Below is a summary of the principles governing the CoG and its relationship with stability.


Other things being equal, (a) the lower the centre of gravity, (b) the larger the area of the base of support, (c) the nearer the LoG to the centre of the area of the base of support, the more stability will be exhibited in the stance.
When giving or receiving horizontal impetus, greater stability in the stance can be gained by widening the base of support in the direction the OF horizontal force.
Other things being equal, there is a corresponding increase in stability with an increase in mass.
The greater the friction generated between the parts of the body contacting the supporting surface, the greater the stability.
The more weight bearing segments IN LINE with the force acting on or being projected by the body, the greater the stability.
A disturbance of one or more of the body's balance mechanisms reduces the chance of the equilibrium being maintained as well as produces a reduction in the volition of movement.

If we are to understand human movement, we need to understand the principles and forces, which work on and through the body. Part of the difficulty in isolating these principles and/or determining their influences on the body lies in the fact that there are innumerable ways in which the body can move or be positioned. Bearing this in mind, I have attempted to describe some of the principles governing human movement and their relationship with the Centre of Gravity in a simple fashion, and give a few examples OF where these principles have not been applied to their greatest advantage.

The above information is representative of that which is presented to our students. Rather than give ready answers to questions asked, we feel the student is better served by having to investigate his own structures and movements, armed with a fundamental grasp of the underlying principles, than by hand feeding him with answers that may have little to do with efficiency of movement and more to do with established dogma.

About the Author
Andrew Williams has trained extensively in two different Wing Chun systems, had his skills tested in numerous real life encounters, and is fast being recognized as an innovative Wing Chun instructor. Williams currently assists Rolf Clausnitzer of the 'Wing Chun Academy of Western Australia'.
David
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