The range of the foot, to my understanding, is the surface on which the axis can "rest its base". Been the axis a line, and the foot a surface, within that area, the axis can rest on many different points, and can displace between them. That the axis rest on a certain point, means that most of our body weight grounds on that point. In this way you can choose to shift the point of the foot where most of our body weight is unloaded, which gives us alternatives.
The range and the inclination of the axis
As said elsewhere, the inclination of the axis is dynamic, always changing, and the rest point of the axis on the base of the foot, and this inclination, are directly related.
Starting from a resting point in the midpoint of the foot (and a bit backwards), where supposedly the axis is perfectly perpendicular to the floor, it can lean in any direction, which will generate shifts on the rest points of it in the foot, in the same direction and in a progressive manner as the inclination. For example, if we stand on the edge of a terrace, leaning forward to look down, you can feel that the area of our toes and metatarsals of the foot is bearing most of our weight. This happens because as the axis leans forwards, displaces itself in its rest point in the range of the foot, also towards the front. Thus, the axis can be leaned in any direction (backward, forward, sideways and even diagonal), which will be moving the rest points.
The range of the foot and the displacement of the axis
Not only the inclination can displace the rest point of the axis in the foot, but also the moving of the axis in a horizontal plane, without changing its inclination.
The best way to graph this, is when we're dancing and we need to step back. As we indicated in the paper where we refer to this, when we walk backwards, we use a forward inclination. Namely, before taking the step, inclination will make our axis rests on the forefoot. But as we begin to move backwards, this rest point also shifts back progressively, although the inclination stays forward, and using in this way all the traction that the foot can give you before releasing the step. This way of using foot traction, can be used in either direction and occupy any part of the surface thereof.
The range of the foot and the free leg
Variations in the rest points of the axis on the foot, can occur both with both feet grounded, and with only one, the latter being the most common case in tango, by the features of this dance. It is very interesting to see what happens with the leg that remains free, and how is it affected by the movement of the axis in the range of the foot base, especially by the changes that occur in the translation in the horizontal plane.
What happens to my understanding, explaining it schematically, it is that the free leg generates a projection in the direction that can be drawn between the midpoint of the foot, and the point where the axis rests. That is, if the axis is resting in the middle of the foot base, and begins to move toward the big toe, the free leg will tend to take the same direction, and gradually begin to be projected onto the same line. In this sense, there is another variable that affects how much the free leg is projected, in the direction already marked. This variable is the bending that can be generated on the base leg, allowing the free leg stretch farther from the body in direct proportion to this level of bending, and pull it back as the body recovers upright posture.
The clearest way to see this is, is what happens when leaders generates lápices in the free leg of the follower. What the leader does is to affect its axis, moving it in its range in different directions and at different heights, which are emulated by the free leg of the follower. When understanding this mechanism, combining it with torsions, you can "draw" with the free leg of the follower, since direction and projection can be perfectly handled.
The limits of the range and the beginning of movement
As mentioned, the axis can move freely within the range of the foot, either by inclination or by displacement in the horizontal plane. But there comes a point where the axis movement abandons these limits. When the axis exceeds these limits, the body becomes unable to stay balanced by itself, so it must appeal either to compensation that can be given by the other body with whom is dancing such as in a volcada or a colgada, or due to be exceeded the “no return point” when the range of the foot is abandoned, inevitably the step must be taken towards the same direction in which the projection was started.
This is the mechanism that operates at the beginning of most weight transferences. A deliberate unbalance of the axis occurs in either direction, either by inclination, by horizontal displacement, or as usually occurs, by a combination of both. This work is the engine, that assisted by the force of gravity and the force of the base leg traction on the foot, that allows us to move our body in the direction of choice.
But it also exist the possibility of “building momentum” before taking a step, like when we prepare to jump. In this case, the axis first rests grounding the body weight on the foot part opposite to the direction we wish to take. That is, if we do a step backward with momentum, first the body prepares in the front of the foot. Furthermore, the body can make other arrangements, including contracting the column from its curvature like a spring, among other things, which I will discuss at another time.
It is possible to change the point where the axis rest on the stand base, and thus affect the area where the weight is grounded, either through the inclination of the axis in one direction, or by the displacement of it in a horizontal plane using the traction that the foot can provide. To this range of possibilities I call "Range of the foot", and this area has its limits, that overcome, must be compensated by the other body, or become displacements. How the axis moves within the range of the foot, will give us different possibilities as it is the result that this has on the free leg, allowing it to take progressively the same directions, that those that the axis takes within this area.