More from the article:
Drawing from the foregoing discussion, I propose that the constituent elements of the biomechanics of balance are stability and mobility. After all, if a standing person has perpetual movement and a moving person (e.g., a runner) has intervals of stability, then it seems prudent to examine both stability and mobility in any analysis of balance. Because horizontal, rather than vertical, forces appear to be the greatest threat to balance, the focus here is horizontal. The stability component of balance refers to the body's resistance to change of horizontal position. The critical features of stability are the body's position, typically represented by LoG, and the BoS. Each of these features can vary
independently along its own continuum. The range of values for LoG and BoS in the anteroposterior (A-P) plane are depicted in Figure 1. The greatest potential for stability is represented at the centers of the continua, and the greatest potential for instability is represented at the ends. Because both LoG and BoS are elements of posture, they often can be assessed at the same time.
LoG LoG LoG LoG LoG
behind near back centered near front in front
BoS of BoS in BoS of BoS of BoS
No Small Large Small No
BoS BoS BoS BoS BoS
Figure 1. Stability Continua
The mobility component of balance refers to the horizontal movement of the body. Variations in the direction and velocity of the body in the A-P plane are depicted on the continuum in Figure 2. The greatest mobility is shown at the ends of the continuum and the greatest immobility is shown at the center.
Fast Slow No Slow Fast
backward backward fore-aft forward forward
movement movement movement movement movement
Figure 2. Mobility Continuum
The relationship between stability and mobility is complicated. First, there is generally an interplay between stability and mobility. For example, an increase in stability (e.g., enlarging the BoS) may lead to a decrease in mobility (e.g., slowing of forward movement). Second, the interplay between stability and mobility may be more or less harmonious. That is, alterations in one component may lead to either beneficial or detrimental changes in the other component.
Third, the desirable proportions of stability and mobility depend on the context: An archer desires high stability and low mobility, a sprinter wants low stability and high mobility, and a ballerina seeks low stability and low mobility. In sum, balance is defined here as the harmonious and contextually appropriate interplay of stability and mobility of the body with respect to its BoS. Presumably, less skillful performers and less successful performances are characterized (in many cases) by less harmonious or less appropriate control of stability and mobility. For a better understanding of this, we can investigate how movers of distinct skill in diverse sports resolve the riddle of balance.
Now in tai chi we teach and practice this interplay between mobility and stability. The trade offs between stability (wide stance) and mobility (narrow stance) are very obvious when it comes time to move, or when it comes time to not be moved. And whether we are spinning and kicking from a single ball or heel of the foot platform, or internally neutralizing the external force of a push, alignment is always key. Even when we jump, momentarily leaving the ground, and kick. We often speak of our continous dynamic balance as the ability to let some parts loose balance as other parts gain balance. Very much like Chris's balance from the core.
Skiing parallels this for me. Whether my skis are on the snow or not. When I feel like I'm skiing well, I don't feel off balance or out of balance. Though my balance reference may move between external ski/snow contact (bottom up reference) and an internal core reference (stability from the core radiating outward to the extremities), I feel balanced. Internal structural awareness is a big part of this IMO. Functional fitness training is a big part of this as well. Whether you choose something like tai chi or another martial art, or a western approach like the pipe, disk, and ramp exercises in the book ProBodX, the body can be trained.
P.S. Won't hold the formating in figures 1 + 2. Sorry.