Continuation of power, continued

July 25, 2009

I didn’t intend to make this a series when I wrote the first post, but after a bit it occurred to me that I talked a lot about how to continue kinetic energy through a movement, and I didn’t mention anything about stopping. Stopping, you say? Isn’t this all about not stopping? Well, no.

Even if you look at a continuous sequence of motions, there are tiny pauses in the movement. For example, if you’re performing a kesagiri (a diagonal cut from shoulder to the opposite hip) followed by a kiriage (a diagonal cut upwards along the same path), there has to be some moment at which the downward movement of the sword stops and the upward movement starts. Yes, you can (and should!) circle the movement at the bottom and prevent an actual moment of stillness, but it’s physically quite difficult to figure out how to redirect kinetic energy 180 degrees without losing a significant amount of it. So, given this (quite common) sequence of cuts, how do you manage to achieve “continuation of power” when you can’t get continuous movement?

Here’s the trick: energy can be converted from one form to another. For the purposes of this discussion, we’re only talking about two forms of energy: kinetic, and potential. It would be really cool if you could convert the energy of your sword movement to, say, light, but sadly that only happens in anime. Kinetic energy is obvious – it’s the energy of the movement itself. When the movement stops, no more kinetic energy. Potential energy is energy stored in some mechanical form; for this purpose, there are two kinds that we’re interested in: gravitational, and elastic.

Gravitational potential energy is the easier of the two to understand. If I hold a sword up over my head, it has gravitational potential energy. If I just stop holding it up, it will come down all by itself, and all I need to do is to steer it into an angle for a good cut. So, if you imagine reversing the sequence of cuts discussed above (kiriage and then kesagiri), the kinetic energy of the kiriage turns into gravitational potential energy as the sword rises, which then turns back into kinetic energy as the sword falls again. All I, the swordsman, need to do is to stay out of the way – to not use my muscles to kill the kinetic energy as the sword falls (by holding it up). So, this is an easy way to continue power between these cuts, even if all the kinetic energy goes away between them (i.e., the sword stops entirely).

Unfortunately, there are two major limitations to gravitational potential energy. First, and most obviously, it only works downward. If the two cuts were, say, a yokogiri (horizontal cut) from left to right followed by another yokogiri from right to left, gravity isn’t going to help me at all. Second, there’s a sharp limit to how much energy can be stored as gravitational potential. If I want to store more energy, I need to raise more mass. Since I don’t want to throw my body into the air, in practice I’m pretty much limited to the weight of my arm and sword, which is not enough to perform a powerful cut.

Elastic potential energy to the rescue. This type is harder to understand, but far more important. The trick here is to think of your muscles, tendons, and ligaments as springs. You’re storing energy by compressing or stretching these tissues, and then letting them spring back to their original length. This is easy to demonstrate: stand up (or sit up straight in your chair), and twist your torso at the waist as far as you can. Feel that force trying to turn you straight again? That’s the elastic quality of your muscles. Body tissues are extremely elastic – it’s possible to store a very large amount of energy this way, for a brief moment. Of course, if you overload them, you’ll end up with pulled muscles and strained ligaments, but you learn pretty quickly what your limits are.

So, at this point, you ought to be able to see where this is going. You perform a yokogiri, let the movement cause your body tissues to compress and/or stretch, and then let the release of that elastic energy turn back into movement the other way. You’ve just done two diametrically opposed cuts, without using gravity, and without having to generate any new energy for the second cut (more or less).

The trick is to figure out the positions and tensions that you need in order to make this work, and there’s no way for me to write that down. In general, if you relax enough (see my very first post, The Secret), and do a lot of repetitions, you’ll find it on your own. Once you understand it, you can work to make the movements smaller, until it’s not visible that you’re doing this at all. It doesn’t have to be a gross body movement – all you need (ha!) is to direct the energy into the appropriate body tissues, which you can do by applying proper tension to the muscles that you don’t want stretched.

The upshot of this whole thing is that you look like you’re generating new power for each cut or movement, but you’re not. Kinetic energy becomes potential energy becomes kinetic energy again, and all you need to do (again, ha!) is to steer it in the direction you want each movement to go. This is not easy to learn, but the payoff is big – you can continue power through almost any movement, linear or otherwise, and your energy expenditure is dramatically decreased. Now you, too, can work your students to the bone without breaking a sweat, and just smile when they ask how.


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