To answer this question, it helps to define what we mean by ‘posture’…
Whether we are standing, sitting, walking, running or lying down, there is always our body.
Posture is the relationship of the parts of our body. You could say it is the way we configure ourselves as a very real object in space; it is our postural relationship, or the way we configure the parts of our body.
Our postural relationship is a combination of what is automatic and of what is learnt. That is, we have an automatic mechanism for being upright which underlies all that we do, and we have the way we have found to use that automatic mechanism.
Of course, we configure ourselves in different ways, depending on what we are doing.
So for example, standing requires something different of us to sitting.
Moving between these activities demands still further changes.
Postural relationship is therefore, to a certain extent, dynamic and fluid.
This is a good thing because life demands flexibility.
However, there is a problem.
If we have learnt to use the automatic mechanism with too much muscular effort, we compromise our flexibility.
Joints become stiffened, and we interfere with the best configuration.
(The best configuration of all of the parts of the body is one using minimum effort to stay in balance.)
Worse still, we make a habit of doing things this way.
Muscles we tense unduly for specific activities become muscles we tense unduly for all activities.
Our stiff back and shoulders, braced knees and tense neck then accompany everything we do, even though none of this extra muscular work is needed.
This is not good because unless we are free to adapt ourselves appropriately to what we are doing, everything becomes much harder work and we risk hurting ourselves.
Thinking about posture as a correct ‘position’ is therefore unhelpful because regaining and maintaining flexibility cannot follow from adding more fixity and rigidity.
This is why in the Alexander Technique, posture has nothing to do with standing to attention, chest out, chin up, bottom tucked in, and so on.
In applying the Alexander Technique to daily life, what we seek is a dynamic relationship of all of the parts of the body — co-ordinated, efficient, and working for us rather than against us.
The Technique offers a sound method for adapting yourself effectively to the task immediately to hand by keeping the best postural relationship in whatever you choose to do.