Robert Barton 

Over the years the most common problem area about which I have been asked has been the human knee, or more appropriately, problems with the knees of martial artists. In fact I have taught seminars just on this subject alone. While these problems usually effect adults, many of the factors of causation start very early in the career of students. There are actually several very common causative things, which can be addressed to improve the health of the joint. The most troubling thing for myself as an instructor is that most

people do not have any concern for these areas until they begin to become a  personal problem. If more instructors would take the time to address these specific factors in their students from the start of the training career, we would see a serious drop in the number of sports related injuries to the knee.

            First, we should talk about the structure of the knee. From a physical and mechanical engineering aspect, this joint is a nightmare. With design weaknesses dictated by requirements of movement which itself slowly destroys the joint. The knee joint is built by bones that sit end to end, held in place by soft tissue and lubricated by fluid. The bones do not fit together like a hinge, nor does one fit inside of another, they just sit next to each other with all joint integrity provided by soft tissue. The soft tissue starts with the bursa which is a padded space between the bones made of synovial membranes, lubricated by synovial fluid. This bursa is designed to keep friction down between the moving parts of the joint. There comes next, the cartilage which sits between the joint to provide shock absorption and cushioning for the ends of the bones. The ligaments run across the joint connecting the bones to one another, ligaments are made of a strong pliable material and are the primary factor in joint integrity. Tendons are the same

type of material as the ligaments, but they connect the muscles to the bones and allow the muscles to provide movement to the joint. All of these soft tissues surround the joint in a protective sheath which both holds the knee together and allows it to move.

            The first factor which I would like to talk about is that of knee joint and relative foot positioning. Poor relative positioning of the knee and foot can put unusual directional stress on the knee joint. Though the knee has a wide range of motion over a specific functional area, repetitive movements and positions should be kept within a smaller safe zone as much as possible when the joint is bearing weight. The general rule of thumb for martial artists in practice is to keep the joint between two points from slightly less than completely straight to a bend of no greater than 90 degrees at knee and ankle. An easy way to identify the slightly less than straight angle requirement is to push against a heavy but moveable object such as a car. The body already naturally knows this position as the maximum extension point of the joint when doing strength related work. By pushing on a car we can see the point where the leg has reached extension and releases pressure to take a step forward. This position is not quite straight to the point of the joint being locked or hyper-extended. The student is then always watched to make sure that they do not over extend the joint into a backward bend during training. The three most common points where this hyper-extension occurs are: in the back leg when the student is in a front stance or posture, in the supporting leg while kicking, or in the kicking leg at the very end of a full speed kick that does not connect or is thrown in the air during practice.

            Slow motion kick training is of great value in teaching the body to not hyper-extend either the kicking or supporting leg. By performing kicks in a slow, relaxed and controlled manner, the movement is patterned into the muscles and brain and the proper form becomes a habit. The natural knowledge of the maximum power transference point is patterned into the new kicking movement as it is being learned. It is a good idea to allow a student to rest a hand on a wall for support, this allows the student to concentrate only on the form of the motion and not have to spend time on concerns of balance and

stability. Some kicks such as the common side kick can be practiced form a position sitting or kneeling on the ground. By removing all other concerns from the mind of the student while a new movement is being learned, or an old movement is being corrected, the student is able to give total focus to the movement and it becomes patterned habit far sooner.  

            The beginning or intermediate student should never throw kicks into the  air at full speed, kicks should be thrown at no more than 75% of full speed unless they are being thrown against a padded shield or bag. These students should only throw full speed kicks against a kicking bag of about thirty-five pounds for an adult, less for children. A kicking shield should be held lightly enough to provide the same amount of resistance, never lean against the kick of a partner or student, allow the shield to absorb the snapping energy at the end of the kick. By kicking this weight resistance, the snapping shock of the kick is absorbed and the kick is slowed down at the end of the movement so that momentum will not snap the leg into a momentary hyper-extension. By kicking a weight that provides more resistance than thirty-five pounds, the shock of hyper-extension is replaced by the shock of hitting something to heavy. While it is true that when kicking another person, the body will give far greater resistance than the ideal training weight, but this is occasional, what we are trying to prevent is constant repetitive movement damage from constant shocks to the joint.

            Another damaging positional factor is when the joint is constantly bent beyond 90 degrees while bearing weight. When the joint bends to a sharper than 90 degree angle, the stress of supporting the weight is no longer being transferred from bone to bone, but is starting to be transferred through the ligaments. If this type of stress is regularly put on the ligaments, they can begin to lengthen or stretch, the result of which makes the joint unstable and causes loss of joint integrity. The simplest way to pattern the appropriate angle into the student is to make sure that the knee is never extended forward beyond the ankle during training. If a line is drawn on the leg of the student from the point of the ankle to the back of the knee joint, that line should never lean forward so that the top point is forward beyond the bottom point when bearing weight. This should be watched very closely when the student is in a front stance or related postures. If a form or Kata calls for extremely low stances, these should be achieved by lengthening the stride rather than bending the knee beyond the ankle.

            The last primary problematic positional factor is foot position during forms and kicks. Many people have a habit of shifting the weight onto the ball of the foot a great deal during forms, or of standing on the ball of the foot during kicks. This unfortunate habit causes a lot of tension in the lower leg which is transferred to the knee. The heel and arch of the foot should be supporting the weight most of the time. The instructor should make sure that the foot is in full contact with the ground when it is supporting weight. If a student shifts their foot position in preparation for a kick, they should return the heel to contact with the ground at the contact moment for the kick. One trick to get students to keep proper weight distribution is to tell them to press down with the heel when kicking or when in stances during forms. But do not allow this to become a stomping motion when moving.

            By close attention to these details and by clearly explaining to the student what is required in the movement, these training techniques can greatly reduce the wear and tear on the joint from regular daily training. Another major area of concern which I wanted to address is something that I touched on above. Constant heavy shocks to any joint are damaging, we need to find ways to reduce these shocks in training. Excessive force applied to the joints can cause the cartilage to begin to break down and the bursa to become dry and inflamed which in turn leads to arthritis. A good instructor can greatly reduce the amount of excessive impacts the joints of any student receives. The joints of children are still growing and are very susceptible to these sorts of damage, but often do not show the effects for many years.

            Above, I mentioned the use of a lighter weight bag for practicing kicks. Think of it this way, what you are trying to do with a kicking bag is to improve the aim and focus of the student. This provides a target that they can aim at and focus their mechanical energy into; this helps to meet these training goals. But what effect does the long term impact on the bag have? First it prevents damage from the joint going into a full speed hyper-extension allowing the student to go full-power without the risk of long term effects from the joint snapping all the way to full extension. This is accomplished by the fact that the foot strikes the bag near the end of the kick and absorbs the mechanical energy so that the momentum of the motion is slowed and the mechanical energy does not focus into the knee causing repetitive separation or over-extension. The damage done by repetitive separation is that the ligaments which maintain joint structural integrity may begin to lengthen which causes the joint to have a bit more play and less strength.

The inverse problem develops when we use a bag or object which is too heavy to stop the kick properly and introduces too much inertia into the process. At this point we are kicking an object which does not safely slow the kick, absorbing the force safely. The heavy object causes the kick to transfer the mechanical energy back into the knee and hip joints. If a student were to kick a wall or tree full force repetitively, they would suffer damage very quickly and noticeably. An excessively heavy bag causes the joint to be damaged much slower and the connection between this and early onset of arthritis and general knee problems often is not made.

The perfect weight to use for an adult kicking bag is 35 pounds which has just enough inertia to absorb the damaging edge of mechanical energy from the end of a kick while not causing the inverse compression of the joint by trying to stop the kick cold. When a kicking shield is used, we need to be sure that we do not resist the kick too much. We are using the shield to slow the kick and check form and focus, we do not have to lean in or give heavy resistance in order to do this.

            When working with the still developing bodies of children I recommend a kicking shield rather than a bag. This allows the teacher to provide just enough inertia to the end of the kick, without the risk of long term impact damage. The instructor is also able to observe form very well from this angle.  A master level artist has learned to use muscular control to decelerate this motion and prevent this sort of damage. Masters can kick into the air all day without a problem, but students do not have the fine level of form

and control on these techniques. As instructors we sometimes forget this and allow our students to do things which will cause repetitive motion injuries.

The last major area of concern is the loss of joint integrity through improper stretching and or unbalanced muscular development. Because of the location and structure of the knee, it is the most susceptible to these two effects. I group these two together because they both cause a weakening in the soft tissues that are supposed to support the joint and allow it to maintain integrity.

The knee joint is moved by muscles which work in opposition to one another they are in the front and back of the thigh. Martial Arts training generally strengthen both sets of these muscles and there mutual strength helps to support the joint. There is a set of muscles on the outside of the thigh which moves our leg outward, this group is also strengthened by general Martial Arts training. The fourth set called the thigh adductor is on the inside of the thigh and closes the legs together. This fourth set is usually not well developed by general training and ends up being much weaker than the other three sets. What results is that the knees have a pull on the outside that is not balanced with a pull on the inside which may cause the ligaments on the inside to stretch out a bit and reduce support on the inside of the joint. The addition of ligament extension and muscular imbalance can cause a serious problem waiting to happen. There is also an imbalance in how the cartilage is able to absorb pressure and this often leads to pain from a joint that is being pulled slightly out of alignment. The joint will show excessive wear in spots much like an unbalanced tire will wear down on one side much faster than the other.

Many sports facilities have machines which are designed to address this particular muscle on the inside of the thigh. Another exercise which can be used is to repeatedly squeeze a pillow or large ball between the knees. Place a partially deflated basketball or similar size soft object between the knees just above the joint where it meets the thigh. Give a slow squeeze of at least two seconds for 20 to 50 repetitions. Daily practice of this exercise will help to rebalance the knee joint and provide strength to the inside of the joint to offset the pull of the developed muscles outside of the joint. It should also be noted that some traditional systems use kata designed to develop these muscles of the inner thigh Sanchin kata of the Goju system is an example of this.

            Improper stretching damages the joint integrity when it transfers the stretch from the tendons which are the intended target for the lengthening effect to the ligaments which should not be lengthened. The stretch is supposed to help increase the length of muscles and the tendons that attach them to the bone, this provide greater range of motion and prevents cold muscle injuries. If a stretch is transferred onto the ligaments of the joint,

they lengthen resulting in a looser joint with less soft tissue support. There are three primary ways in which stretching can damage the ligaments by transference of the focus: poor posture/bad stretch positions, bouncing in a stretch position, spending too much time in a given stretch position.

Most Martial Arts instructors and dance instructors have their students do stretches that are traditional as they learned them. Many of these positions put undue stress on the ligaments by being badly designed positions. Any type of standing splits stretch is going to severely affect the ligaments around the knee. This is the worst offender in the commonly used postures, and should never be used under any circumstances. In fact I will strip rank from any of my BBs who I catch teaching or allowing a student to do this.

The splits can only be safely used when the person is flexible enough to sit all the way down so that the weight of the body is being put onto their rear end. If the student is standing with the legs at an extreme angle, the pressure of the weight of the body id being borne laterally to the knee. This results in the stretch being immediately place onto the ligaments of the inside and back of the knee. If the student slips, their entire weight will come down onto the joint and result in serious soft tissue trauma. 

Bouncing during a stretch results in an uneven pressure which often causes the muscle to overstretch and get microscopic tears in the muscle fibers. When the muscle overstretches, the pressure starts to fall onto the ligaments in a hammer like fashion. The end result of this is that the muscle is less efficient and the ligaments are looser.

Even in a good posture with the steady, even, controlled pressure of a static stretch, the muscles can become overstretched by being pulled for too long a period of time. When the muscle goes beyond the safe zone, the stretch energy and effect transfers to the ligaments around the joint.

The general rule for regular large muscle stretching on a daily basis is to hold a position for 20 to 60 seconds. When dealing with smaller muscles, the time should be shortened to 10 to 20 seconds. For the first 20 seconds of a stretch, a large muscle is going out to maximum extension as it relaxes and steady pressure is applied. The initial 20 seconds of the stretch is what prevents injury during a workout, and these stretches should always be 20 or more seconds in length. For the next 40 seconds the tendons are actually increasing their length and potential range of motion. After a total of 60 seconds, muscle fibers will begin to give way inside of the tissue of the muscle, and the pressure will begin to shift over to the ligaments.

            Now that we know what not to do with the knees, what rules can we apply to our training and teaching in order to prevent knee injury in ourselves and out students? A basic formula for students and instructors of the Martial Arts to follow in the development of good skills while minimizing the damage done to the knee would implement these principles into training at all times. By consistently following these principles instructors and students alike will find that their knees are healthier and stronger and remain so for a much longer period of time. So let's list some of these details and suggestions:

Proper stretching should never include a bounce, but should be a steady static type of stretch. Overstretching should be avoided by keeping large muscle stretches to no more than 60 seconds. Injury should be avoided by a good warm-up prior to a workout, this warm-up period should include gentle range of motion exercises and steady stretching with large muscle stretches being done for no less than 20 seconds. Any stretches that place lateral pressure on the joints should be replaced with healthy stretches that make use of the natural alignments of the body stretches that should not be done include: standard hurdlers stretch, standing splits and any partner type stretches (partners cannot feel what is going on in your body and these almost always result in overstretch damage to the soft tissues).

Generally, postures and stances should not bring the knee into a bent position beyond 90 degrees while bearing weight (the knee should not be out past the ankle in a common front stance). While it is true that the knee is bent well beyond the 90 degree mark when chambering for a kick, the joint is not bearing weight and is not under any stress. Kicking and standing legs should never be allowed to hyperextend, and students should be monitored carefully to insure that the knee is only going out to the ideal strength extension point. Weight should remain evenly distributed across the foot, and not be pushed forward onto the ball of the foot. This can easily be accomplished by telling the student to stand or kick with a feeling of pushing down the heel of the supporting leg. Even when the student raises onto the ball of the foot in order to pivot, the foot should be planted at the end of the pivot, and should be planted during a kick.

            Beginning to intermediate students should not kick full speed into the air during practice. Most students do not learn to control this type of force until second or third degree black belt, though a knowledgeable instructor can develop this skill in students of a lesser rank. Slow motion kicking is an excellent way to develop this type of awareness of the body, as is medium speed kicking while standing in water that is chest high. Slow motion kicking should be a large part of the learning procedures for the basic kicks, even master level students should do most of their practice kicks slowly.

When kicking a bag, the bag should be of a weight that has enough inertia to safely slow and absorb the speed and force of the kick. Thirty-five pounds is the ideal weight for the average adult. A 35 pound bag will absorb the snapping force at the end of the kick but will not turn the force back into the knee. Children should kick hand held shields, and the instructor should regulate the resistance, so that it is just enough to safely slow the kick without turning the force back into the knee joint.

I hope that we all remember to incorporate these things into our training and teaching, especially those of us into whom students and parent place their trust.

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