To elaborate on planes of motion and centering, I attach the Da Vinci sketch at the left. If you observe the diagram carefully, you can see the center of the circle is not at the head or chest of the man. It is at the waistline. Specifically, in Japanese martial arts this point is called Tanden and represents the center of gravity --- a very important point in aikido, jujitsu and judo.
When I teach throws, I am always careful to emphasize how important it is not to just pull or push the opponent, but rather to concentrate on moving the line of their hips. This means that we should be trying to get their tanden to rise off the ground, at which point we can easily unbalance for a sweep or load the opponent onto our own hips for a throw. Likewise for defense, consciously keeping your hips low and away from your opponent is a central tenet of judo.
When fighters are mismatched, one being much taller than the other, there is often a tendency for the shorter to reach up to grab his or her opponent. Instead, I would suggest focusing on connecting the taller person to your hips/tanden and bringing them DOWN. Connecting them to your hips/center has a dual effect of making them easier to move, since you move them with your hips and body weight rather than just your arms, as well as compromising their balance by making their spine bend to meet your hip line. In good aikido it is very common to redirect Uke's arm to your belt line before using a control or a throw - good examples include kote gaeshi, shomen irimi nage and tenchi nage. Even for techniques which start on a higher line, such as Ikkajo, it is important to "row" the motion back to the hip line in order to get the maximum power. My teachers used to advise me to "put their hand in my front pocket" meaning to bring Uke's hand and arm down to my belt line before executing the throw. I have tried to remember this idea in my practice since.
The idea of the "dynamic sphere" is expressed in Oscar Ratti's excellent book "Aikido and The Dynamic Sphere" and clearly illustrates not only the principles of centering (connecting to the hips) but also of centrifugal force, which is the foundation principle for spinal rotation techniques (tenkan) in aikido, where we use the spinal axis rotation by pivoting to capture, control and project or guide uke to the ground. Spinal rotations driven by the hips also serve to disperse an attacker's aggressive energy by dissipating it in a circular flow around us rather than making us receive it directly into our own balance and structure. In Kali it is rarer to use such pivots, but the principle is the same when we pass using Suliwas or other parrying flows.
Of course, centering is an important metaphor outside the dojo as well. Every day there are many things which happen that could cause us to reach out and lose our balance instead of remaining centered. Breathing, posture and focused movement are just as important in our everyday lives as they are in our training.
Stay Centered.
