One exercise that can be practiced at the beginning of any yoga class (particularly when there are lots of beginners) is lengthening the spine and then relaxing it.
The spine is a difficult body element to learn to feel and control but we can work towards feeling the spine by first learning to feel and control the ribs relative to the pelvis and the head relative to the ribcage.
We can then use this as a general action within any yoga pose, including warrior 1.
So that we don't have to worry about stability we can start in a seated position and practice bending the spine backwards and forwards.
Actually what we can start of with, since the spine is too big and too general (it has 24 vertebrae after all), is moving and feelng the sacrum and the pelvis.
The sacrum can be moved relative to the pelvis creating movements called nutation (nodding forwards) and counter-nutation (nodding backwards).
This is movement happens at the sacro-iliac joints, where the sacrum connects to the pelvis. You can learn to control these movements using the lower transverse abdominus and the pelvic floor muscles. However, now the goal is to use the sacrum as a reference for moving the pelvis. So rather than moving the sacrum relative to the pelvis, now we are trying to move the sacrum and pelvis together, as one unit.
Some movement between the sacrum and pelvis may occur, but for now we'll ignore it. Unless it causes pain that is.
Generally, people don't tend to think about their pelvis as a whole and so when in the past I've talked about tilting the pelvis forwards or backwards my students don't really "get it." However, the sacrum is easy to feel and recognize, it's the triangle of bone at the base of the spine that sits between the buttocks and points to the anus. It's easy to feel, it's part of the spine and moving it not only moves the pelvis is also causes the spine to move also.
And so, lifting the sacrum causes the pelvis to roll or tilt forwards while dropping the sacrum cause the pelvis to roll backwards. If the ribcage is kept upright then these movements cause the lumbar spine to bend backwards and forwards.
By bending the lumbar spine back and forwards the lumbar erectors turn on and off repeatedly and if the movement is smooth enough and slow enough and if awareness is directed to the lower back, which is just above the sacrum, the practitioner can learn to feel the spinal erectors activating and relaxing.
A lot of teachers seem to teach this very same exercise on all fours or while laying on the floor (locust pose.)
I'd argue that the upright position is better since we spend most of our time upright anyway.
When lifting the tailbone, the focus can shift to feeling the lumbar spine erectors activating. The focus can then be on magnifying this feeling, making it feel stronger. The backbend may increase as a result. For the opposite movement, I tend to prefer a relaxed sinking of the sacrum. Here body weight can be used to sink the pelvis down, the weight of the ribcage and head pressing down via the spine through the sacrum to help cause the pelvis to tilt back. By making the tailbone lifting phase of this exercise more active, so that the spinal erectors activate, and the lowering phase more relaxed, it can be easier to focus on and learn to feel the spinal erectors and the lumbar spine.
The goal of this exercise is to learn to lift and expand the ribcage, but to get there I find it easier to start with "feeling" the sacrum, and then from there the lumbar spine, and then from there to expand the movement to include the thoracic spine.
Generally what I try to get my students to do (and I'm not always effective in explaining or teaching this) is to carry the feeling of the lumbar spine bending backwards up into the thoracic spine.
If you've got the feeling of the lumbar spinal erectors contracting then carry the contraction up into the thoracic spinal erectors.
Often I find some students retracting their shoulders to assist in bending their thoracic spine backwards.
If that's the case and they can't do otherwise then I'll do an exercise to help them learn to feel their shoulders then invite them to do the spinal back bends without using their shoulders.
And that's cool because shoulder awareness is an important element in warrior 1 anyway.
Continuing with the spine and ribcage, after some time bending the thoracic spine backwards and then relaxing the next step is I to focus awareness on the front of the ribcage, the chest.
What happens to the chest when the thoracic spine is bent backwards?
It moves upwards, away from the pubic bone. And it expands or opens meaning the ribs slide relative to each other in such a way that the volume within the ribcage increases.
From there the instruction can now be lift the chest (bend the thoracic spine backwards) and lower the chest (bend the spine forwards.)
Generally I find that people often have difficulty lifting and lowering their chest straight off the bat and so it is easier to start with the sacrum, the lumbar spine and then work on the thoracic spine and ribcage.
Since the ribs attach to the thoracic spine any movement of the thoracic spine will affect the ribcage.
This doesn't mean that every time I ask students to lift their ribs I also want them to bend their thoracic spine backwards.
But at a beginning level when I'm first trying to teach conscious proprioception, it helps to work on bending the thoracic spine backwards in order to open the chest.
Now often I don't talk about the breath.
Instead I have them smoothly and slowly bend backwards and forwards, and if they work on this the breath naturally follows since this action naturally increases and decreases lung volume.
And so the movement teaches them breath control via learning to control the muscles and bones that drive the breath.
Students thus get a taste of learning to feel their breath by feeling the movements of the muscles and bones that cause breath in the first place.
Too further exercise some of these same muscles, a further exercise while seated could be a simple seated cross legged twist, either using the arms to help twist the lumbar and thoracic vertebrae relative to each other or using the intrinsic muscles of the waist and ribcage to do the twisting.
Depending on the level of the students and my own teaching focus this can also be an exercise in conscious proprioception.
As a way of learning to activate the paraspinalis muscles, the smaller muscles that work between adjacent vertebrae, I could have them move their awareness up their spine, one vertebrae at a time, and working on twisting the current vertebrae relative to the one immediately below.
To make this exercise more effective I'll have them count vertebrae, five for the lumbar, five for the lower thoracic, seven for the upper thoracic and seven for the cervical spine. If by the time they've counted upwards for the five lumbar vertebrae they end up somewhere in the middle of the upper back then it's a hint that they can make smaller jumps as they move up their spine.
Generally, when I'm on a roll, this phase of conscious proprioception learning goes quite well.
The movement actually feels good and so I don't have to keep on telling people what to do.