However, recently I've seen a number of people talking about “sine wave motion” again. One person, for instance, wrote on Facebook that one sees all these Taekwon-Do power breaking videos online, but they never use sine wave motion. Another thing I read recently was a small scientific experiment where people punched a bag that was equipped with measuring tools and the subjects punched the bag with sine wave motion and without sine wave motion. The results showed that “sine wave motion” added little to no force to the hits—that the punch without sine wave motion was actually better.
To me the statement about breaking and also this experiment is obviously flawed because the vector in these techniques travel horizontally, parallel with the ground. The “sine wave motion” is not intended to add force to techniques that move horizontally.
It is pretty simple and I don't know why people don't get it. I think it is because of the wrong appropriation of the term “sine wave.” It is not meant to be understood as an actual sine wave. What General Choi tried to explain was the displacement of the body's centre of mass along the vertical axis—up and / or down. If you also move forward and so displace the body's centre of gravity along the horizontal axis it mimics the motion of a wave, which he referred to as a “sine wave”. It was maybe not the best semantic choice, but don't get stuck on the term. See the principle.
What principle? Simply: accelerate as much of your body mass through your technique at the target. That's it.
Sometimes this means bending your knees and dropping your weight for a technique that includes a downward vector. Sometimes it means pushing with your legs up for a high technique. Sometimes it means not going up or down but keeping level, as with techniques that travel horizontally towards the target.
For me the “sine wave motion” (yes it is a bad term, but get over it) simply means I'm pushing my centre of mass upward or letting it drop downward, depending on the direction the technique is travelling towards the target.
Now some might say, that's not sine wave! Their reasoning is that ITF Taekwon-Do's “sine wave motion” always have three parts: down-up-down. Once you understand the principle of relaxation, activation, and execution that is taught through the “sine wave motion” one need not exaggerate them as is often done as a training mnemonic with the “sine wave motion.” The “sine wave motion” is a training tool used to teach principles of motion; it is not a cookie cutter that should be stamped onto every technique. Every sensible ITF practitioner knows this.
But enough about that—I've written about the phases of the sine wave motion enough elsewhere; let me quickly explain why I say the above experiment and breaking observations are based on wrong assumptions.
The “sine wave motion” contributes to vertical force—the rotation of the hip contributes to horizontal force. If the target is to be reached at a horizontal plane, adding vertical force (through dropping of the body weight) will not contribute to the force of the technique. However, if the target is at a downward angle so that the vector includes a vertical (i.e. downward angled) trajectory, then dropping the body weight will obviously contribute to the technique's power.
What people don't seem to get is that a large percentage of Taekwon-Do techniques reach their target not directly perpendicularly horizontal, but often at a slight downward angle. In other words, many Taekwon-Do techniques incorporate both horizontal (i.e. hip rotation) and vertical (i.e. body-dropping) forces.
Here are a few examples of techniques to which “sine wave motion” contributes.
Obviously, low techniques where the dropping of your body weight into the technique clearly contributes towards the force of the technique, for instance a low punch, low block, or low kick.
Most middle techniques too. For instance when doing a punch, the arm is not held up at the top level of the shoulders, but a little below the shoulders, so that the punching arm is not exactly parallel with the floor, but actually angled downwards a bit. Imagine standing in front of somebody your own height and punching them in the solar plexus, the fly ribs, or the kidneys. How should your arm be angled to achieve this?
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| The brachial nerve is reached at a diagonal angle, not horizontally. |
Many blocks in Taekwon-Do divert the attack not merely sideways, but rather sideways and downwards.
Also, when I started Taekwon-Do over two decades ago my instructor insisted that most kicks should reach the opponent at a downward angle. The sidekick was taught as a “stomp”, the front kick as a “trample”, the turning kick as a “clobber” like with a sledgehammer for which you use gravitation to aid you in the technique. High kicks were never prioritized and even when kicks were performed high, the admonition was that you should hit with gravity as the kick was on its way down.
Let me point out that all these examples of "Taekwon-Do work[ing] with gravity" (as my first instructor used to say) are from my basics. These are techniques I learned over twenty years ago in a Taekwon-Do gym where nobody every mentioned “sine wave motion.” I only learned of the term after I had my first black belt.
Setting up breaking boards (or measuring equipment) to be hit with fully horizontally moving techniques are flawed, I think. If you want to test if “sine wave motion” (i.e. the dropping of the body weight into a technique) adds to the force exerted by a technique, then you should set-up the experiment for techniques where this makes sense, where dropping the body weight into the technique is actually measured. That's why, when I teach breaking techniques to my students we hold the breaking boards at various different angles and heights.
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