Yoga pose side bends can be used to stretch the side of the lumbar spine, thoracic spine and cervical spine, by bending them to the side.
They can also work on the hips and the sides of the thighs.
And they can also be used to work on the shoulders, though defining a side bend for the shoulders is a little bit difficult.
A very basic side bend in which you can work on all of the above regions of the body is standing side bend.
In this pose it is very easy to isolate each of the above areas when working towards the full version of this pose. As an added bonus you can also practice balancing while doing this standing yoga pose.
Standing with feet about hip width apart and parallel, first lengthen your spine. Then push your hips to one side. Then bend your lumbar spine and thoracic spine in the opposite direction. Then reach your arms past your head.
A side bending yoga pose in which it is easier to focus on bending the spine is to sit cross legged, bend forward and then reach the arms and torso to one side. Since the pelvis is on the floor the pelvis is held in place making it easier to move the ribcage relative to the pelvis. You can then focus on lengthening one side of the waist and the ribcage.
When side bending the waist or lumbar spine, you can tilt (and bend) the ribcage relative to the pelvis. You could also tilt the pelvis relative to the ribcage to bend the lumbar spine.
As an example of this, while laying on your back you could bend your ribcage to one side while keeping your pelvis stationary. Or you can tilt your pelvis to one side while keeping the ribcaage stable.
In a standing forward bend, you can lengthen your right waist by pulling your right hip back. You can also pull the right ribs away from the pelvis. Then you can do switch and stretch the left side. Try to make both sides feel the same.
If you can't touch your hands to the floor in a standing forward bend then rest your hands on the seat of a chair or even rest your elbows on the surface of a counter or table top.
If you have some muscular imbalances in the muscles of the hips and waist this yoga pose side bend may help in correcting them.
When doing a side bend one side of the waist is lengthened and the other is shorted.
And so there are two ways to focus on a side bend for the waist.
While doing a standing side bend to the left, you can focus on contracting the left side of the waist. You could instead focus on lengthening the right side of the waist. Or you can do both.
Side bends for the spine can become more interesting when done in combination with other actions. If nothing else they can improve awareness. But they can also help the pose that you are doing. As an example, if I am working towards wheel pose I might warm up in bridge pose and include as part of my warm up side bends for the waist while I am in bridge pose. With my pelvis lifted I'll move one side of the forwards (away from the ribcage) then I'll move the ther side forwards.
One of the reasons that I do this is because I've got some imbalance in my spine, waist and hips, and this is one way to help correct the imbalance.
I sometimes try to do the same in wheel pose.
While doing the side bend in bridge or wheel I shift my weight from one leg while I am side bending. It can happen naturally as a result of the side bend. Shifting from side to side gets both legs working equally in these back bending yoga poses.
Another opportunity for a side bend is while doing a spider man chest stretch equivalent. This pose is done while bend forwards facing a wall with the hands on the wall. The main focus of this pose is sinking the ribcage but you can practice turning the pelvis from side to side to lengthen one side of the waist and then the other.
It's relatively easy to side bend the lumbar spine. However you can also practice bending the thoracic spine sideways. In a side bend for the lumbar spine the obliques on the short side can be contracted to help increase the side bend.
In a side bend for the thoracic spine the intercostal muscles located between the ribs can be used. So that you actually have room to bend the ribcage to the side you may find that it helps to expand the ribcage and create space between the ribs.
This space may give you more room to bend the ribcage to the side.
To balance the forward bend I'll do a high lunge yoga pose as a back bend for the hips. And in this yoga pose I'll also occassionaly side bend the waist, first to one side and then the other. I may also side bend the ribcage.
When in a side bending yoga pose the ribs on one side move away from the pelvis while on the other side they move closer. When side bending the ribcage, the ribs on one side move away from each other while those on the other side move closer together. If you also side bend the neck in this standing yoga pose, then one side of each inter-vertebral joint opens and the other side closes.
One option for side bending the shoulders is to reach the upper arm into the stretch. Doing a side bend to the right, reach your left arm over your head to the right. Elbow straight. Grab the wrist with the right hand and use the right hand to pull the left arm to the right. Optionally you can also pull the arm down.
Personally I like to resist the stretch on occasion. The easiest way to do this is to bend the left arm. Pull down with the right, and then while continuing to pull down, slowly straighten the left elbow.
Another option is to start with the arm straight. PUll down with the right arm and at the same time pull up with the left arm.
To balance this stretch for the shoulder you can pull the arm down and to the opposite side behind the back. A similiar stretch is to sit in a chair and grab the edge of the seat with your left hand and reach your torso and head to the right.
This may help to stretch the upper fibers of the trapezius muscle. Meanwhile, reaching the hand up and over the head may stretch the latissimus dorsai muscle.
Note that in standing side bend, to stretch the side of the hips and the thigh, push the pelvis to the side using the legs. If bending to the right push the pelvis to the left.
Seated side bends include having the legs in an easy version of the baradhvajasana position with one leg in hero and the other in tree pose position. Bend to the hero leg side.
In this case the side bend can be used to add weight to the hero leg and help to stretch the single joint fibers of the quadriceps.
You can do a seated side bend with the legs wide. You can also do a side bend with one leg in janu sirsasana or tree pose position. Or you can do it with one leg in hero position. In either case you can focus on lengthening the long side while inhaling. While exhaling you can contract the muscles of the short side. And to make it easier to move your torso towards your leg, imagine lifting the leg so that the leg muscles activate.
To focus on the spine relax the arms. Then add the arm and if you life grab the foot.
Note that if shoulder flexibility is limited in this position you may want to read up on using the trapezius muscle in lifted arm positions.
More active side bends include side balancing pose and plank pose.
Generally thought of as a twisting pose, twisting triangle can include a side bend of the spine to get the back leg shoulder over the foot before entering the twist. With the spine bent to the side, and with the hand on the floor, it can then be easier to subsequently twist the spine to the front leg side.