6 - Stretching
Stretching is one of the most important activities a martial artist studying Tae Kwon Do can participate in.
First of all, in order to execute the highest quality techniques you are capable of, no matter what level you perform at, your body must be properly warmed up, and stretched out.
Secondly, the number of injuries you are likely to experience as a result of your training is dramatically reduced by proper stretching techniques.
Finally, your body's recovery after a training session is much faster and more complete if you stretch properly.
6.1 - A Short Discussion of Your Body's Structure As It Relates to Stretching
The majority of your muscles work with your bones by contracting, and thereby applying force between the bones; this is the basis for almost all movements that your body can make. Some muscles do work without the benefit of applying force to bones (your tongue and your heart are good examples of this), but they are not important to this discussion.
In order that they might apply force to the bones, the muscles are attached to the bones by tendons. Bones are generally attached to each other by ligaments at the joints.
Muscles are made up of individual muscle fibers, which are either relaxed, or contracted. Muscle fibers do not ever partially contract - they are either fully contracted, or relaxed. An individual muscle fiber cannot change the intensity of its contraction; so the way a complete muscle increases the overall force it generates is by contracting a larger number of fibers. This is called "recruitment" - just like recruiting more soldiers to do a bigger job, your muscles recruit more fibers to perform more work.
Contraction occurs because deep inside each muscle fiber, flat plates coated with special chemicals overlap each other; the body's nervous system stimulates the plates electrically, and they move towards each other. The larger the overlapping plate area, the stronger the contraction. This is one of the reasons why when your arm is extended and the bicep is stretched, your ability to close your arm is weak - the plates are pulled away from each other and there is less overlap; hence the muscle can generate less force. Conversely, if your arm is halfway closed, the plates are in a well-overlapped state, and so much more force can be generated.
There are three types of muscle fibers, two types of fast-twitch and a slow-twitch type. Slow twitch fibers are smaller in diameter, have greater blood supply, generate greater force, get tired less easily, and (as the name suggests) are actually slower to generate force. Fast-twitch fibers are larger, have less blood supply, generate less force, get tired sooner, and contract at higher speed.
All three types are generally present in all of your muscles. For training in Tae Kwon Do, it is preferable to have fast-twitch fibers predominate, as speed is a key factor in a large number of Tae Kwon Do techniques. Normal Tae Kwon Do training - that is, attempting to strike, block and move as quickly as possible - will cause your body to naturally increase the number of fast-twitch fibers in your muscles.
Surrounding the muscle fibers is an elastic material ("elastin") combined with a strong, inflexible material ("collagen"). These are contained in a substance which acts both as a lubricant and a fixative.
Muscles generally work in pairs; for each motion there is an agonist, which does the work of the movement, and an antagonist, which work against the motion being made and also will perform the role of the agonist when the motion is reversed. For example, when you close your arm, the bicep is the agonist, and the tricep is the antagonist.
6.2 - Stretching: What Happens?
When you stretch a particular muscle, first the individual muscle fibers stretch, and then the connective tissue around the fiber stretches. Interestingly, just as when a muscle is contracting only some fibers participate, the same occurs when stretching. Some fibers stretch - others don't. You can easily see then that the more fibers you can get to stretch, the better the stretch will be - the longer the muscle will get overall.
Special nervous system elements ("proprioceptors") are located in the nerve endings of the muscular system; in the muscles, and in the tendons as well. These "report back" to the nervous system about the state of the nerve with regard to how much pressure it is experiencing at any one moment. When you stretch a muscle, these nerve endings trigger a reflex which works against the stretch - it causes the muscle being stretched to attempt to contract, which of course in turn reduces the amount of stretch. This reflex works normally to prevent muscles from over-stretching in response to a sudden load. The side effect here works against your purpose - to stretch. However, if you hold your stretch for a while (usually 15-20 seconds is sufficient), the reflex begins to "back off", and accordingly the muscle will begin to elongate further. By continually stretching your muscles, as is normal in Tae Kwon Do training, the reflex will become less intense, allowing greater initial stretching capacity.
6.3 - What Needs To Be Stretched
Although it is useful and healthy to stretch all muscles that will be used in a workout, the key to high performance is to concentrate on the muscles that will be used either at, or past, the normal end of the range of motion for those muscles when they are unstretched. Here are two examples that should make this idea clear:
6.3.1 - Muscle Used In Range
Extend your arm fully, so that your arm is straight, until your elbow prevents the arm from going any further. This is a normal motion for your arm, even though it extends all the way to the end of the range of motion. No further motion is possible because the elbow joint is locked, yet this is completely comfortable for most people.
Now close your arm, until the pressure of your forearm against your bicep prevents further closure. Again, this is a normal motion for your arm, no further motion in this direction is physically possible, and it is completely comfortable. Since in fact there is no additional range of motion available, it is obvious that the arm will not be used beyond its normal (and in this situation, maximum possible) range of motion.
In the case of the bicep, stretching will not, actually cannot, extend the range of motion nor make the bicep significantly less injury-prone. For this reason, it is not important to stretch the bicep.
6.3.2 - Muscle Used Out of Range
Stand with your right leg back and your left leg forward, feet about one foot apart. With your leg kept perfectly straight, gently throw the right leg forward and up, towards your head.
This stretches out the right hamstring, which is located in the back of the right upper thigh. At some point in its travel towards your head, the leg will come under significant tension from the hamstring, and it will cease rising.
Your leg's maximum possible range of motion as determined by the hip joint is actually much further than this; in fact, you could put your foot right behind your head if the hamstring didn't prevent such a move - the hamstring is normally too short to allow this, however.
This kicking motion is therefore one which reaches the end of normal range of motion. However, in the practice of Tae Kwon Do, this muscle and related muscle groups are used to this point and in fact well beyond it. Extending this range of motion is therefore a worthwhile and highly sought after goal of the training, as it directly results in better kicking techniques.
Because this muscle is used beyond the normal range of motion, it is important to stretch it carefully and completely before attempting to use it.
6.4 - Warming Up
It is critically important that you warm up before you begin to stretch. To warm up most effectively, utilize movements that have short range of motion, such as short hops, medium knee lifts, and short punches.
The objective is to break a sweat. This indicates that your core temperature is coming up, that you are "warm" in the true sense of the word.
When warm, stretching is easier, less likely to injure you, muscles reach greater final stretch extents, and the effects of the stetches themselves (muscle memory) last longer.
6.5 - Stretching Methods
There are a number of types of stretching methodologies: