Imagina a set of basic principles that can be applied to doing yoga poses. Ideally, these principles can be used in any yoga pose at any time.
The idea of these principles is that you can use them, where necessary, to help you understand what to do in a pose. That can mean using them to break down a pose into basic elements, or knowing what to do in order to deal with problems in any particular yoga pose.
They are a way of looking at, modelling and understanding your body, the pose you are doing and the relationships within those two things (your body and the pose that you are doing).
So that these principles are more meaningful we can relate them to the five elements of Taoist philosophy: Earth, Water, Metal, Fire, Wood.
You could think of earth as having the quality of stability or support. Water has the quality of fluidness or connection or flow. Metal has an analytical quality. We can use it like a knife to cut something into pieces so that we can study it. Fire is expressive or passionate. As for wood, it connects, expands and move outwards. It can also be thought of as expressive.
In the context of basic principles you could look at the subject of anatomy as metal since it helps you to understand your body. Learning to feel your body and control it could be listed under connection since both actions involve the flow of energy; in one case into the body and in the other out of it. Different styles of yoga, say Ashtanga or Meridian, could be listed under Expression.
In the first case, part of what you can do is create a stable foundation as I did in the flow sequence.
In all cases you can create foundation and make it stable by engaging the muscles in such a way that they work against each other to support and stabilize the joints in question.
In a standing yoga pose you can work from the ground up, engaging feet and shins to stabilize feet and ankles. You can then engage the front and back of your thighs and shins to stabilize your knees. Depending on the pose you may or may not choose to stabilize your hip joints.
In arm balances where one or both legs are somehow "connected" to your arms then it might be helpful to think in terms of dual foundations. Your arms support your upper body but then your leg (or legs) which is/are on your arms can be a foundation for your pelvis.
In such poses you can first stabilize your base (your arms) then, to stabilize the connection between your legs and arms you can "press" your leg or legs against your arms.
In binding postures, if you are wrapping around a leg, you can make that leg a foundation i.e. marichyasana A. If you grab your hands in ardha matsendrasana (as opposed to the foot) you can make your top leg stable so that you can push against it to deepen your twist. It then acts as a foundation. Likewise, with respect to your hands, you can consider one hand grabbing the other to be the foundation for relaxing your arms as much as possible, assuming you have a strong grip.
In a posture like navasana where you are balanced on your sitting bones, you can make your torso strong, intergrate or unify the parts of your torso or spine using your abs, so that it acts as a foundation for keeping your legs lifted.
With a foundation you have a base for then directing your effort, like the way a foundation for a building serves as a base for actually constructing the building.
If a foundation is a base for what you are doing, the opposite extreme is the expression To create an expression, know what you are trying to do. Actually, this should come before even the foundation. You have to know what you are trying to do before you lay the foundation. Oh well, I've listed it as the second principle but this illustrates that these basic principles aren't necessarily hierarchical. But anyway..
You might like to think of this as expressing the pose. Note that it can be challenging to draw a line and say the foundation is here and the expression there. As an example, in standing poses, is the foundation your feet, your feet and shins, your feet, shin and thighs or does it include the pelvis?
I'd say be open to all interpretations and choose the one which works best given what you are trying to do. If you know what you are doing you can get on with doing it, hence expression.
Pick the expression that you like or that fits what you want to do.
In this case, even though your pelvis might end up pushing back, you can think of your pelvis as your foundation.
But we're talking about expression. Well it relates to foundation, the two are opposite sides of the same coin, elements of the same idea. What may be important is picking a foundation that helps you to better express what you are trying to do and so your foundation may be the part of you in contact with the earth or it may be part of your body that is still or stable or integrated/unified.
Pick what works, and if you don't know what works, experiment and find out what does.
More than anything, when picking a way to express yourself, a foundation can act as a zero point or datum helping you to better define the direction (or directions) that you are expressing yourself in.
So that you can create a foundation, so that you know your legs are solid in Warrior 2 you need to be able to feel your legs.
At the same time so that you know you are reaching your ribs up and your arms out you need to be able to feel your shoulders, arms, hands and fingers. And you need to respond. If you aren't reaching out fully you can act by spreading your shoulders, making your elbows straight and reaching with your fingers.
I use the term connection to refer to the acts of sensing or feeling your body and controlling it.
Connection allows the flow of sensory input and it allows you to respond, to choose your actions. Connection means you can feel. It also means that you can respond to what you feel.
If you can't feel parts of your body, if you can't breathe, then reposition yourself so that you can. Then gradually work deeper while maintaining your ability to feel and control your body. To make this easier practice moving slowly and smoothly, both into a pose and out of it. You then improve or maintain your ability to control your body and sense it. You connect to it.
What's a general rule for how to respond? Make room. Make room for the parts of your body to move relative to each other given what you are trying to do. Make as much room as you can while still maintaining your ability to feel and control your body.
Room to move and connection are complementary. Connection tends to mean or imply being relaxed, close, loose, sensitive. Room to move implies expansion, openness, effort. In between these two extremes is center and balance.
In any posture, center implies being aware of your whole body whether you sequence your awareness through your body or feel it all at once. That can mean understanding your body and/or the pose that you are doing.
It also means being aware of your foundation, expression, connection and of room to move. Center is being present both in your body and in what you are trying to do, even if that means at the time that you are trying to figure out what you are trying to do.
I picked the earth as foundation for reasons I hope are obvious. We all stand on the earth and it supports us. However, in terms of basic principles and yoga poses, foundation is also the part of our body that is stable and strong and that supports the rest of our body in what we are trying to do. And just as the earth is a foundation for ourselves, so is the sun the "foundation" for the earth. Foundations are relative. We can choose them based on what we are trying to do and our point of view at the time.
Water represents connection because of its flowing nature. It is the flow of information and energy into ourselves and out of ourselves. By being aware of this flow we can channel and direct it.
Metal represents center in a number of ways. First in the form of a knife we can use metal to dissect a pose so that we can become aware of its elements. But in the form of a nut and bolt we can use it to hold the parts of a pose together.
Fire represents room to move becuase it expands outwards. The idea is to control the amount of heat so you create just the right amount of room to move. After all you want to maintain connection. And so you can think of fire and water balancing each other. Not too hot and not too cold.
Wood represents expression in the way that an artist or artisan might carve a piece of wood to create cabinets, desks, tabletops or a work of art, beautiful in its own right. Knowing what you are trying to do you can guide the way you use your senses, the way your create your foundation and how you tie together and unify the parts of your body in what you are trying to do.
These basic principles for yoga poses are ulimately a way of becoming present.
Because you are feeling and controlling your body you may find that thought stops, or at least is being directed in such a way that you are focused on what you are doing now. You may reach a point where you can feel and operate your body all at once. Prior to that you may be scanning your body so that you can sense and control it an element at a time.
Eventually you may drop the principles or not have to think about them because you understand what you are doing. In that case you can get on with doing it and enjoying the experience of doing.
Why improve muscle control?
Muscle control not only helps you to control your body, it also helps you to feel it.
Muscle activation creates the tension that not only moves your body, but helps you to "sense" it.
With better muscle control you can use your body with less effort and make it easier to balance, improve flexibility and deal with pain and poor posture.