Webs of Tension, Isolated Compression
Tensegrities respond to stress by changing shape and redistributing stress throughout their whole structure.
In a tensegrity, tension elements are all interconnected while the space creating elements (often referred to as compression elements) do not directly connect.
Space creating elements float so that within a tensegrity, they have some freedom to move relative to each other. Because the space elements can move relative to each other, the tension elements can freely and easily share stress.
Tensegrity via Inflation
A balloon is a tensegrity. The rubber of the balloon's skin acts as the tension element. It is entirely connected. Meanwhile the molecules of air inside the balloon are the space creating elements. Free to move relative to each other they push outwards against each other and against the skin of the balloon.
Push in on the balloon at any point and it responds. Tension is distributed throughout its tension network. Meanwhile the space creating elements redistribute because they are free to move relative to each other.
Tensegrity via Compression
A bicycle wheel can also be viewed as a tensegrity. The old type made out of steel are easier to understand in this regard.
The spokes are the tension creating elements.
The hub and rim are the space creating elements.
Viewed from the side the rim pulls outwards on the spokes. Viewed on end (say from the front or rear of the bike) the hub also pushes outwards on the spokes.
The spokes are connected to each other via the hub and rim and this allows them to share tension. The uppermost spokes have the most tension supporting the weight of the bike and rider. And while rolling, as the spokes approach the uppermost position they experience an increase in tension. As they approach the lowermost position their tension decreases.
There is a certain amount of pre-tension so that even when in the bottom position each spoke still has some tension.
Go over too big of a bump then you bend the rim. But then if the bend isn't too excessive, you can use a spoke key to adjust tension in the spokes near the bumps. You can then use that tension to pull the rim back into shape.
(The rim is perhaps the most easy to damage part of the structure. Would a segmented rim, with each segment held in place by spoke tension but also with shock absorption between the segments offer a more damage resistant structure?)
These two examples show two opposite ways to go about creating tensegrities. One is through expansion, filling a balloon with air. The other is via compression, adding tension to the spokes of a bicycle wheel.
Maintaining Shapes or Changing Them
Trueing rims was something I tried doing when I was younger since I was so good at finding bumps to ride over.
While trying to true my own rims I could feel the changes in tension. The more tension a spoke had the harder it was to tighten it further. I could also pluck or tap a spoke. This was generally useful to see if a spoke had too little tension or not tension at all.
I bring this up here because in the context of our bodies, it is important to understand that space and tension can not only be used to maintain our body in a particular posture or form, varying them can also be used to change our shape, to create movement. And just as importantly, this space and tension (and pressure) can be used to help us feel our body as well as control it.
Trueing a bicycle wheel I had to used muscular effort to turn the spoke key to add tension or subtract it. Actually turning the key could give me an idea on how much tension the spoke was under. Increasing tension would pull the rim one way, decreasing it would allow it to move the other way (if there was something to pull it that way.)
Ideally I fixed the wheel in such a way that no spokes had excessive tension and the wheel was "true" at the end of it all.
Because I was using tension to fix a bend in the rim I also used my eyes to see when the rim was aligned.
Putting together a wheel from scratch the idea isn't to use tension to true the rim, since the rim is already true. Instead it is to add enough pre-tension so that the wheel can handle the stresses of riding.
- Too loose and the wheel will probably shake apart.
- Too tight and then the wheel elements might not last so long or be less effective.
- Within the range of usability, less tension may give a more comfortable ride while more tension will create a more responsive wheel.
And so one of the qualities of a tensegrity is adjustability or "tunability."
Choosing the Degree of Tension for Performance
In a youtube video, one tensegrity enthusiast built two tensegrity units, one with wires for the tensioning elements the other with elastics.
Both had different properties and different responses when subjected to drop tests.
The creator did this as an experiment but also suggested that more athletic bodies might be better represented by the model with wire tension elements and more sedentary types by the model with elastic tension elements.
Enhancing or Reducing Elasticity while Running
I'd suggest here that the quality of elasticity can be controlled or varied by muscle tension. The ability to maintain muscle tension despite sudden shocks will mimic the less elastic model. The ability to vary muscle tension in response to sudden shocks and then return to the "pre-shocked" state after the shock would mimic the more elastic model.
As an example, running on the fronts of the feet, someone with a lack of experience would allow their heels to sink during each foot strike. Someone with more experience could maintain the shape of their foot through the foot strike and subsequent or simultaneous shifting of weight to that foot.
Generally, when running on the fronts of the feet, it helps to have the weight forwards so that each time the lead foot touches the floor, it is already supporting the weight of the body. If the weight is behind the foot, then the foot will strike first and then the weight of the body will shift onto it.
Tension Induced Pressure Awareness
How do you tell if you are running with your weight back?
By feeling your feet. If you weight is back you'll feel the ball of your foot touching the floor. If your weight is over your lead foot then you'll feel the toes and forefoot touching with approximately equal pressure. The instant the foot touches down, tension is added to the toes and this tension helps to create pressure in the toes. Tension in the foot and ankle also helps to create the instantaneous pressure sensation in the ball of the foot.
Even if you aren't a runner you can experience this while walking slowly.
I'd suggest that (with training) we can choose or vary the amount of tension that we create and so vary the tensegrity state of our body. We can choose to be more elastic (for a smoother, more comfortable ride perhaps) or we can choose to less elastic (for greater efficiency.)
Choosing the Degree of Tension for Sensitivity and Strength
Whether moving or being still we can vary tension for strength and sensitivity.
At the very beginning, if we are learning to feel our body via tension, then the more relaxed we are, the more we reduce unnecessary muscle tension, the easier it is to feel connective tissue tension.
This is tension can can be created in our tendons and ligaments and in the non-contractile connective tissue within our muscles. This is the type of tension we learn to feel while moving slowly and smoothly and while as relaxed as possible.
I'd suggest here that the slowness and the relaxation is so that we can learn to feel and control our body, so that we can maintain tensegrity from movement to movement. As we get better at moving smoothly while feeling our body we can then carry that smoothness and awareness into moving quickly. And we can continue to feel our body even with additional tension.
But even with the ability to feel tension and control it, why might we choose the minimum amount of tension necessary? Because it maximized sensitivity. But also because it can be a way to stay engaged in what we are doing.
When doing yoga poses the goal could be that of creating maximum space or length with minimum effort and with tension throughout the body so that the whole body is involved.
Anatomy and Integration via Space and Tension
Our body is neither a bicycle wheel, nor a balloon, nor a tensegrity toy, though it can share similiar properties.
Elements like the skull, the pelvis, the spine, have all been modelled successfully as tensegrities. One group worked on modelling the suture joints of the skull. With their model they couldn't push the individual bones of the skull together. The sutures and the shape of the joint kept the individual "spacing" elements apart.
Even the elbows, knees, and other joints of the body can be modelled as part of a tensegrity structure.
Rather than bones resting on top of each other, the joint capsule holds the bones together but at the same time allows them some movement relative to each other (the way each end of a spoke has some freedom where it connects to the rim and hub).
The liquid inside the joint capsule can be thought of as a space creating element. The combination of joint capsule envelope and the fluid inside ties the ends of the bones together but also keeps them apart so that they have the freedom to find the best position relative to each other.
(Dr. Levin relates first hand experiences of knee surgeries and seeing the bones being pushed apart.)
Muscle tissue has been found to connect not only to tendons, but also to the joint capsule so that muscle tension also affects the joint capsule as well as the relationship between the bones it works on. Increased joint capsule tension would increase the pressure of the joint fluid, which then resists the ends of bones being pushed together.
(It may be that) because bones like the pelvis and skull are held together and maintained by space and tension, they can actually grow. And it is because of this quality that women can give birth with both the baby and the woman's pelvis remaining intact.
Muscle Tissue, The Engines that Maintain a Posture or Change It
Muscles are the engines of shape changing and shape maintaining.
By adding to, subtracting from or maintaining muscle action, tension is maintained or varied not only to bones but to the joint capsules. In turn this tension can affect other muscles. Those muscles might be opposing muscles, those muscles may be stabilizing muscles or muscles that share a similar action. They may also be muscles that are part of the same anatomy train or connective tissue meridian.
Lets return to the bicycle wheel for a moment.
Varying (or Maintaining) the Relationship Between Spacing Elements
Imagine replacing the spokes with muscle tissue embedded in connective tissue.
To add tension the muscle contracts. To relax tension the muscle relaxes.
Imagine being able to control all the spoke muscles. Imagine by adding tension to backward angled spokes, you could rotate the rim relative to the hub. Imagine adding tension to the spokes that attach to the same side of the hum, you could shift the hub relative to the rim. Or you could combine these actions. And you could see the effects of these actions by noticing (eyeballing) the change in relationship between rim and hub.
Now imagine that you can measure or sense the output of each muscle. You could calibrate muscle action with changes in relationship between rim and hub. You'd then be able to reliably change relationships based on muscle effort.
Measuring Tension and Changes in Relationships
But what if some external force changes the relationship between rim and hub. Then you lose calibration. So now, instead of just muscle action you measure tension within each spoke. The muscle might be part of this measuring mechanism. You measure muscle length and tension.
In a zero external stress condition you measure muscle action and tension against changes in relationship between hub and rim. Maybe you move rim relative to hub and measure changes in tension. Then you use muscle action to create the same changes, recording the amount of tension required, or the different combinations of tension that create the targeted change.
What is the maximum effort configuration? What is the minimum effort configuration? What is the configuration that best shares stress among all components?
Rather than hypothesizing or theorizing, we can actually try these things out and experience them. (Notice how "experience" has a similiar root to "experiment.")
Once this experience is under the belt we begin to play with tension, smoothly varying it in different conditions and noticing the changes that occur.
Then we begin to add external perturbations. Again we play with tension versus relationship. How do we maintain a relationship under certain conditions, how do we move between two relationships under certain conditions?
Noticing the relationship between wheel and hub, noticing tension and muscle action, we can learn to change relationships or maintain them no matter what is happening.
We've developed the ability to sense and the ability to respond.
Using Tension to Feel and Control Relationships Within Our Body
With our "muscle-wheel" we can notice the relationship between the space elements, the hub and rim.
The tension elements can tell us (or give us a good clue) when a desired condition is arrived at.
Getting comfortable with different external stress conditions (experience) can tell us how to reinterpret tension readings so that we stay centered or as centered as possible. If one set of spokes gets too slack then add tension to the opposing spokes to reduce the slack and maintain the relationship between hub and rim.
If tension is maintained in all tension elements, then even if external conditions change, tension can be immediately shared without excessive stress to any of the components.
With the human body, much the same rules can be applied to create a posture or action that has tensegrity.
To give a yoga pose space and tension we can work on creating and maintaining space between the space creating elements, the bones.
At a minimum we can create space in the spine by first learning to move ribs away from pelvis and skull away from ribcage.
This can later be expanded to stacking or aligning the vertebrae for maximum possible straightness given the conditions of the pose.
Space can be created at the shoulders by moving the shoulder blades in the direction that the arms are reaching.
Space can be created at the hips by reaching the thigh bones out of the hip socket.
Simply creating space can be enough to add tension.
Further tension can be added by creating compression along the long axis of the arm and leg bones.
Draw the elbow towards the shoulder joint or vice versa. Draw the knee towards the hip joint. In addition try drawing the wrist towards the elbow and the ankle towards the knee.
Try to create space first, then add the tension on top of it.
Once you get a basic feel for this, try to vary the tension. Slowly go to maximum, then see what the minimum tension is that you can create while still being able to actually feel that tension.
I'll suggest that unless you are lifting weights, look for the minimum tension while still maintaining feeling.
The control of tension can then then be further refined by learning to activate or relax muscles at will. The better we get at feeling tension and controlling it, the better we can choose the optimum tension.
Optimum tension is somewhere within the range of the minimum tension we can feel and the maximum tension where we can still respond in the minimum amount of time necessary.
Maintaining our body in a state of tensegrity we can both feel the elements and control how they relate. Via our body we can feel any changes and respond in such a way that we maintain space and tension
Published: 2014 01 03