02 Stability (Grounding)

posted 7 Jul 2011, 21:21 by aikidorepublic   [ updated 5 Aug 2011, 02:55 ]
Stability is probably the most important thing to the martial arts, from stability comes the ability to develop and to receive power. The power available to a stable, centred person is infinite scientifically and only limited by their structure.

How do we know this, well the ground is what holds up 80 storey building, trees and us, as gravity presses us into the ground the ground pushes back with exactly the same force, effortlessly and in exactly the same direction. Its quite amazing, cosmic even...no wonder grounding is considered so important. What if we can harness this power??

Accessing Infinite force

The force that the ground pushes back with is called the ground reaction force. if you look at the simplified diagram (man in a box) below you can see that provided the force is applied in a direction that goes into the ground the ground will push right back. internal strength exploits this by adjusting the direction of applied force to enable externally forces to be received and by aligning the body so as to use the ground reaction force (GRF) as a springboard for ones own power.

A simplified series of models

To explore grounding it is neccessary to make the problem simplier, in fact so simple that no maths is needed but enough that there is conceptual reality


A simplified model. Physics is confusing mostly because it gets very complicated very quickly and the best way to describe something is with mathematics - which is a barrier to many. However the real beauty of physics is to break down a problem into managable solveable chunks. This is the approach taken here, where a person is represented as a box of fixed height, a centre of mass and a base of support. In this simplified model there are no linkages and joints that can flex, thus is one part moves all parts move.

Static model

Most of the analysis is confined to the static model, mostly because its easier to describe.
 The extension to the more complex models is fairly straightfoward beginning with the passive model where the body can be considered as a series of linkages. Here muscles take up slack and tendons can store and release energy like springs.
Push on the shoulder and it collapses a little, in fact control the stiffness of the collapse and you can redirect the direction of the applied force closer to the ground so there is less energy to fight actively

Passive model

Active Model
Here the linkages can be considered to have active elements that generate and push back this is a rough analogue of the muscles and tendons in the body
Active model

Stability defined
Stability is defined by three elements, the centre of mass of an object(COM), the height of the COM and the Base of Support (BoS). While these can be described mathematically the conclusions are somewhat self evident

Base of Support - A wider base of support makes a n object moe stable, thus (b) is more stable than (a)

Height - A higher centre of Mass is less stable than a lower one, thus (a) is more stable than (b)

And of course a larger Mass is more stable than a lighter one.