I am reposting this blog post from October 17, 2009. Again, it is so that I can discuss the subject further.
Back to mechanics.
In Kishaba Juku dojo, we work hard on body dynamics. That is an understatement!
Sometimes I say that we are like racing car mechanics. We are trying to customize our students (and ourselves) for maxim speed, power... dynamics.
Sometimes I will see a student who has worked on developing a good koshi movement, which essentially is the use of whip-like (core driven torque) mechanics in all Karate movements. But some students are like a firecracker that sizzles -- just a dud. The whip is there but there is no power (or very little).
Most of the time, the reason for this lack of power is because the student has not yet learned to put his weight behind the block, strike or other movement. The "crack of the whip" is there, but it is just fluff.
It is important for our movements to be light and heavy. We move lightly, but at the moment of explosion and power transfer, all or much of our weight should be behind the movement. This is usually accomplished by shifting weight in different ways. Imagine a whip with a hammer at the end.
My point is that koshi is just part of the formula. It is an important part, but not the whole thing. Usually, when an advanced student has struggled for years to overcome the limitations of linear mechanics, koshi is the answer... at that particular moment. But it is the coordination of movement principles (body shifting, weight shifting, body alignment, delay, koshi, etc.) that leads to results.
Move lightly but hit heavy.
Charles C. Goodin