In Tango Estilo Milonguero turning by spinning or swiveling on one foot and swerving the hips to power the spin is not viable because
(i) this twists the spine causing the tension to be projected to the shoulders which then upsets the embrace, and
(ii) the tension created by this motion is difficult to maintain under control causing further tension and loss of efficiency of movement.
Given that you do not dance tango by walking in a straight line, the question arises how do you perform changes in direction or turns?
To understand this you can think of movement in terms of physics and the energy generated by forward motion. It may be tempting to think of moving forward in line (linear motion) and turning (circular motion) as distinct. In that case, you would be imagining that in order to turn you first come to a dead stop. Then you would need to initiate a new movement to create motion which is circular. That would be like a car having to come to a dead stop every time it takes a turn.
In reality there is no need to stop to make a gradual turn. The forward momentum is diverted in a new direction so long as the turn is gradual and the car is not moving too fast (otherwise attempting to turn would cause the car to lose traction and skid sideways and perhaps even flip over). You only really need to come to a stop or near-stop when doing a sharp U-turn. In tango, gradual changes of direction are like those with a wheeled vehicle, namely, they are just a continuation of the forward motion of the walk and so we are just diverting the momentum in a new direction. Gradual changes of direction are therefore continuous with walking.
However, after we walk a few steps we would normally need to stop and go in reverse. Again, it may be tempting to think that we have to go to a dead stop, but this is not actually the case. Again, when a car stops it does not come to a dead stop instantly. When the car sharply brakes the wheels screech and the car sinks into the suspension before all the energy is dissipated and the car comes to a dead stop. Before the car comes to a deal halt all that kinetic energy is temporarily stored in the suspension and body of the car.
Kinetic energy is stored in structures such as a stretched elastic band or a bungee jumping rope at the bottom of the fall. The couple in a tango embrace can be viewed as a structure that can be characterised by tensegrity, a word which is a contraction of Tensional Integrity, coined by Buckminster Fuller who gives the following definition:
Tensegrity describes a structural relationship principle in which structural shape is guaranteed by the finitely closed, comprehensively continuous, tensional behaviours of the system and not by the discontinuous and exclusively local compressional behaviors.” Quite a mouthful, but he also could say it in a different way, like: “…compression elements in a sea of tension…
If the couple is a structure characterised by tensional integrity or tensegrity, the kinetic energy generated by the linear motion of the walk is stored much as it is in an elastic band that is held stretched. In tango, when you walk as a couple you create the tensegrity that stores energy. Turning is converting the kinetic energy generated by linear motion in one direction, which is then stored in the tensegrity structure of the couple in the tango embrace, into energy to propel the couple either into linear motion in the opposite direction, or circular or rotational motion.
Now, in some forms of dancing the circular motion is done by pivoting or spinning on one foot. Notice that it is not necessary to pivot in order to turn. You can also turn around your axis by taking steps in place. While this may seem like a very static way to turn, in fact it is not and can be performed in a dynamic way that represents the sort of controlled release that we want to convert the linear motion of the walk into rotational or cicular motion of the turn. At not point is there a need to pivot or swivel on one foot. The advantage of not having to pivot or swivel is that you completely eliminate two problems associated with turns: (1) the problem of centrifugal force that causes dancers, especially in high heels, to lose balance; and (2) the problem of potential slipping that is inherent in having a non-sticky floor and shoes that allows for pivoting.
I call this the Principle of Linear Circularity: the possibility of converting linear motion of the walk into circular motion of the turn, which nonetheless feels like one is walking because there is not pivoting or swiveling involved. We are turning even though we don’t feel like we are turning, and instead feel like we are walking. This has the added advantage that we don’t have to separate the practice of walking from the practice of turning: they’re one and the same practice. A turn is just a variation on the walk whereby the linear energy of the walk is converted into circular energy through the action of the feet in walking and the transference of kinetic energy through the tensegrity of the tango embrace.
As you learn this way you will find that the only way you can learn the dynamics of the tensegrity structure is experientially: first, it is useful to develop a better awareness of the tensegrity in your own body by performing simple movements that connect the extremities in the upper and lower body via the spine; and second, by simple partnering exercises in which you learn the tensegrity of the two connected bodies moving in unison, and how the directed action of the feet brings about the redirection of the kinetic energy of the walk.
But why not pivot?
Now that you understand how it is possible to change direction or turn without pivoting, you may be wondering why is pivoting such a bad thing? Pivoting on one foot is such a major part of tango dancing these days that there is a lot of time, money and energy devoted to it: dance floors can’t be too sticky but also too slippery and these are difficult to find or maintain, so we need chalk and instead of dancing in normal street shoes we need special dancing shoes that allow us to spin and swivel, and again there is special maintenance required to keep these in just the right level of non-stickiness and non-slipperiness that we can swivel without falling over. Special technique is required to spin/pivot/swivel without falling over and this of course requires a lot of lessons and practice, not to mention stress and worry.
So eliminating the pivoting/swiveling technique from your dancing you basically eliminate all of the associated time, money and mental energy costs. You get normal shoes that have enough friction to prevent you from slipping. Most importantly, you eliminate all the worry about your balance that is inherently associated with pivoting, esp. for women wearing high heels that are inherently unstable, and thereby all of the technique classes and practice time that could be devoted to other, more useful things. Of course if you live for swiveling and all the moves associated with it are the main attraction in tango for you then I can’t argue with that. But otherwise, you gain a lot and lose little by eliminating this technique from your dancing.