02b Ground Reaction Force

Ground reaction forces
The ground pushes back at the exact angle at which it is pushed. Thus it can be drawn on to push against, or an applied force can be 'drawn into' the ground to negate its power.

The range of angles for which the GRF can be generated out or receive power into is defined by the base of support extremeties to the point of contact. There is optimal and sub optimal toppling angles where  it is possible that some of any applied force will be opposed by the ground reaction force.

For example in the above figure (1) shows an applied force exactly along the toppling line, which could in theory be infinite because it would be opposed by the ground reaction force. If the angle is any more horizontal it will topple the shape and any more vertical it will remain firmly in place by the opposing GRF

This is I think exactly what the Internal strength practitioner manipulates to withstand being pushed - subtle changes in the applied force. This is sometimes explained as the ground path.

The angles that a ground reaction force can make are dependant on the point of contact and the base of support of the person.

The forces that must balance are the ground reaction force , the generated or received force and the weight of the person, if they are not in balance the ground reaction force will be unable to be applied. Again manipulating the dynamics to stop this is the job of the good martial artist/ internal strength practitioner.

This can be manipulated by dropping the body slightly to draw the horizontal force down, or touching under the elbows and pushing them up  to make nage push down a little more like in the figure below.

Image Westbrook and Ratti