Sensational anatomy is anatomy that you can feel and control.
The aim isn't just to teach you names of muscles and bones so that you can pass a test, it's to teach you how to feel and control your anatomy. And so that you don't become reliant on a set of "alignment adjustments" without knowing what the adjustments are for, the aim of sensational yoga anatomy is to give you a basic understanding of the body so that even without the fine tuning you can still create a yoga pose or movement that has the whole body working together in a way that feels good and uses minimum effort.
This is, I believe, a relatively unique approach to anatomy. A lot of anatomists approach the body as something separate from themselves, pieces of meat, bones and perhaps connective tissue laying on a table. My own experience is that we can learn to feel and control our muscles and bones.
For sensational anatomy it helps to understand a few things that aren't currently in the textbooks.
One fairly uncommon idea that is brought up by J.C. (Jaap) Van der Wal MD PhD is that ligaments are arranged in series with muscle tissue. Tendons and ligaments are actually part of the same connective tissue structures and muscle tension affects both muscles and "ligaments".
In the video Jaap explains that ligaments, for the most part dont' actually exist. Instead they are, for the most part, artifacts created by the anatomists knife. Ligaments and tendons are instead part of the same connective tissue apparatus. And so parts of this apparatus acts as "ligaments" when required. And rather than these "ligaments" experiencing tension only in extreme joint positions (which Jaaps views as inefficient) they experience changes in tension whenever there is muscle tension, just as tendons do.
He then goes on to talk about synovial joints as organs that create separation between adjacent bones. And how this could work is that muscle tension creates tension in the walls of the joint capsule that then causes the fluid inside the joint to pressurize in such a way that it helps to push the bones away from each other. These two opposing forces (the pull of the connective tissue "inwards" and the pressure of the synovial fluid outwards) create the possibility of movement with minimal stress to the moving components.
In the video Jaap makes a big distinction between an "architectural" view of the body and an "anatomical" view.
One way that I can identify with this is from my study of electrical and electronic circuits. As an example of this one circuit board may contain many components that do different jobs. To the brain of the computer that the circuit board is a part of, the circuit board itself (like the "anatomical view" of the body) isn't recognized as a separate entity. Instead what is recognized are the individual functions that the circuit board (and other circuit boards) provide.
In Jaaps' architectural view the basic components are dynaments which consist of two aponeurosis (like tendons and ligaments combined) attaching to two different bones and a muscle element that connects them. This basic element can be modified so that one or the other aponeurosis is not present as is the case with some muscles that have no tendon on one end, or it can be modified to not include the muscle element, so acting like a pure ligament. These do exist but are rate and the rational for their existence is that they connect two points for which the distance between them doesn't change for any position of the joint. They remain at a constant length with constant tension.
One other point that I should mention here because Jaap also talks about this in his video is that there are two main functions of connective tissue and that perhaps connective tissue should be classified according to whether it creates separation (and shapes space) or whether it is used as a connection to transmit forces.
Another important concept is the idea of meridians. My first exposure to meridians was via the Traditional Chinese Medicine route. Not that I studied TCM but I did study the TCM meridians since I was teaching Meridian yoga for a short time. Even to this day my understanding of those meridians sometimes guides the way that I sequence stretches or understand what is happening within my body.
One of my assumptions at the time is that the meridians where actually a part of the connective tissue network of the body.
One of the aspects of this system that I like the most is the fact that they include connections to the organs. And what this leads to is the idea that muscle tension can affect the organs and the state of the organs can affect muscle tissue.
Later on I learned the anatomy trains meridian system which ignores the organs (or it does when I first started reading about it) but does focus on trains of muscle linked by connective tissue (the connecting kind.) Because of this, tension in muscles within the same train or line can affect the functioning of other muscles in the same train.
At this point I should talk a little bit about "connection."
Just because all the parts of the body are connected doesn't mean that all parts affect each other all of the time. Instead connection is the potential for one part of the body to affect another. As an example of this, if connective tissue is relaxed then any change in one of the bones that it connects isn't going to affect the other bone. However if the connective tissue is under tension, then change in the position of one bone will probably affect the other bone in some way.
A simple example is anti war protestors who where taught to relax and go slack when the police where trying to carry them off. By going slack they effectively relaxed the connections between the parts of their body so that they become like a sand bag. And those are difficult to carry. At the other end of the spectrum we can tense everything so that our entire body becomes stiff (or stabilized) and then it is easy to move the body as a single unit because everything is locked together.
This is a very useful concept to understand in tai ji since if we relax a part of the body it can give way to whatever is pushing against it, but if we stabilize part of the body then that stability can be used as a foundation to push against our opponent.
And so connection is important but what is more important is being able to feel and control connections, adding tension or relaxing it at will.
For sensational anatomy it helps to differentiate between two types of muscle. Because the intent is to learn to feel and control our body it helps to differentiate between muscles that are big enough, or bulky enough that we can feel their fibers contract and relax and muscles that thin or small or both and so harder to directly feel whether they are active or relaxed.
There are others but the main importance of these types of muscle is that it is easy to feel when they are active and when they are relaxed. And if someone can't feel the difference it is reasonably easy to teach them how.
For the second type of muscles we can learn to feel the effects of their actions by noticing changes in bone position. Or we can deliberately control these muscles by deliberately moving bones relative to each other. As an example we can learn to control the SI joint by moving the coccyx relative to the pelvis using the pc muscles (mula bandha.)
For improved scapular awareness and stability we can focus on deliberately moving the shoulder blade. To feel the serratus anterior muscle, and control it while moving the shoulder blades, awareness can be focused on the upper back, in particular the area between the inner edges of the shoulder blades. When active the serratus creates a "spread" feeling between the shoulder blades and the spine.
The respiratory diaphragm can be felt or notice by its effect on the abdomen and with practice, if you put your mind in the right place you may actually learn to feel it contracting.
Smaller muscle activation is more often the type of muscle action focused on in tai ji and some forms of kung fu. Rather than relying on the strength of bigger muscles to move or position the body the smaller muscles are used. These tend to create subtle changes in tension in connective tissue and foster greater awareness since you have to be more aware to feel these affects (and control them.)
That being said I'll often work with large muscle activation with beginners since it is easy to feel and control and who's to say the ability to consciously activate these muscles, or relax them, won't come in handy.
If nothing else, learning to feel and control the large muscles can give us feedback of the state of our body. It is via muscle activity or its absence that we can learn to feel what state our body is in. And if we learn to feel the subtler tension from smaller muscles, such as when lifting and expanding the ribcage, then this gives us further means of feeling our body and controlling it.
At this point I should mention something that I learned in Social Dance class. As the lead (and this applied to the "follower" as well, the idea was to not hold our body to slack not too tense. We had to have a little bit of stiffness so that we could interact with our partner, but we also needed to vary this stiffness, not too stiff, so that we could feel and adjust our body easily. But another aspect of dancing was monitoring the way that we were positioned with respect to each other.
In dance class one of the things that I was vary aware of was finding the right amount of space between me and my partner (and between ourselves and the other couples around us.) This spacing varied depending on the type of dance and even the type of movement that we were doing but there was a certain balance we needed between having enough space to actually move while not having so much space that we were overextended.
This same principle can apply to muscles. When we adjust the position of parts of the body with respect to each other in a pose or action we can try to balance these relationships so that our muscles aren't over-extended nor, where possible are they too slack.
The ideal is a balance, like when dancing, between too far and too close.
One way to adjust muscle tension is by creating and adjusting space between the parts of the body. Another way is by activating muscles to take up any slack. In either case we take up the slack and in so doing add enough tension to the parts of the body that we can feel them, and also so that we can instantaneously make adjustments. This is because we've taken up the slack. If we don't take up the slack then we lose awareness and responsiveness. Unless a change in tension from slackness to tension is what we are using as a signal.
While tension is a primary mechanism for learning to feel the body, it isn't the sole mechanism. And actually it is changes in tension, or changes in sensation that create information. And so as mentioned above, if we are initially standing as relaxed as possible, then any sudden fluctuations from relaxed to tense is a signal that something has happened.
It's like balancing while standing on a moving train. If we feel an increase in tension (or strength) in our front leg it indicates that the train is decelerating. If we feel an increase in activation in our back leg it can indicate the train is accelerating (assuming in both cases we are standing sideways to the direction of travel.)
A feeling of equal tension between both legs can indicate either that the train has stopped or is travelling at a constant speed.
Another reason for creating a balance between space and relaxation is that when we create balanced tension between the parts of the body, this tension gives us sensation, which then tells us the position our body is in. Some sensation can come from large muscles activating, say the spinal erectors, other sensation can come from connective tissue tension. In both cases, these tensioned elements give us a feel for our body.
While tension gives us clues as to how the parts of our body relates, pressure gives us clues as to how our body relates to the earth. In general, any part of our body that is in contact with the earth of another body is a potential sensing mechanism. With the earth in particular we can use pressure gradients to determine where our center of gravity is with respect to our foundation. The point of greatest pressure (or the line of greatest pressure) is the point (or line) over which our center of gravity is poised.
Working towards the ability to feel our body and control it, it could help to have some sort of overall goal, no matter what it is that we are doing.
Recently a video came to light of a tensegrity robot. It's a vary basic robot build around a tensegrity structure. The designers have the ability to control tension in the tension elements in such a way that the solid members can move relative to each other to move the structure as a whole. They also have the ability to vary tension to the degree that the robot can lay flat, and presumably relaxed in a stowage configuration.
Without the controllability, this type of structure is naturally very robust since it can redistribute stress throughout it's tension elements to share or distribute tension. And part of the reason it can do this is that the solid elements have some ability to move relative to each other. One of the aspects of the construction that gives them this freedom is that they are not in direct contact.
Adding controllability via adjustable tension the solid elements can move relative to each other by varying tension, and by relaxing tension the robot can collapse flat. And that's pretty much the same as our bodies, though our bodies are a little bit more complex. Not only do we have more tension and compression elements, we also have organs suspended from those elements.
The idea here is that we can relax and collapse into a non-rigid form. But we can also add tension and I'd suggest that optimum tension is not too much and not too little. Enough that stresses can be shared and enough that we can feel via this tension.
As a result, two basic qualities that we can look for so that we can work towards this tension integrated state are no slack spots but also no super tense or tight spots. Both indicate a lack of integration. If we have slack spots, this means that the body as a whole isn't distributing stress, and if there is additional stress placed on it, it can't share it. If we have super tense spots, this too indicates that the body as a whole isn't integrated. One or more muscles are taking too much stress either to protect a body part or because they are substituting for a part of the body (a muscle or muscles) that isn't working.
I mention these two qualities in particular because they are both something that we can easily learn to feel and recognize (if we haven't done so already.)
The idea then is to figure out how to balance for those slack spots or overly tense spots so that tension is distributed throughout the entire body.