Back bending yoga poses can be be used to: open the front of the hips, stretch the front of the thighs, lengthen the belly, open the front of the ribcage and in some cases, open the front of the shoulders or arms.
(You could also think in terms of bending the spine and hips backwards.)
Backbends can also be used to strengthen the back of the lumbar, thoracic and cervical spine as well as strengthen the back of the hips and thighs.
In the case of strengthening the back of the neck and the back of the spine in general, the muscles strengthened (or at least used) are the spinal erectors.
One way to practice using the spinal erectors (and to practice feeling your spine bending backwards) is with seated spinal back bends. This exercise uses the sacrum as a major reference point.
Once you can feel your spinal erectors activating while seated you can further your backbending spinal awareness while doing locust pose.
If you focus on feeling the contraction of your erector spinae in locust pose, you can then carry that same feeling into cobra (middle picture above) and upward dog.
In upward dog you can further extend the feeling so that you also bend your lumbar spine backwards using your spinal erectors.
For all of these poses you could start of by doing them with your neck straight so that you focus your effort on the thoracic (and lumbar) spinal erectors. You can then try bending your neck backwards so that you activate your cervical spinal erectors also.
When bending the thoracic spine backwards, backbending can be facilitated by using the levator costalis muscles to lift the back ribs. The feeling is similiar to that of activating spinal erectors and so you may find it easier to lift your back ribs if your spinal erectors are already engaged.
You could also do a similiar action while standing.
For this standing backbend, reach your pelvis forwards and your ribcage back and up. As you push your pelvis forwards you can imagine (or feel as if) you are pulling your feet back, using the floor for traction.
It can be easy for the upper body to sag, and so counter act this tendency focus on making your spine feel long and use your spinal erectors to bend your spine backwards. Use your buttocks and hamstrings (back of the thighs) to bend your hips backwards.
Traditionally yoga is done facing the east and so the front of the body corresponds to the east. Stretches for the front of the body are "East" stretches such as the first pose below (Purvottanasana).
Correspondingly, poses where the back of the body is stretched could be called "West" Stretches. "Paschimottanasana" (which can be translated as "Intense West Stretch") is one yoga pose that stretches the back of the body. However, this pose could also be used to strengthen the back of the body.
Perhaps one of the most challenging areas to bend backwards is the thoracic spine, since it has the ribs attached to it. Bending the lumbar spine backwards is a little bit easier.
It's easy to learn to feel the contraction of your lumbar spinal erectors (a "squeezing" sensation that runs up the back on either side of the lumbar spine) and so if you start with bending the lumbar spine backwards, you can learn to carry this sensation up into the back of the ribcage.
However, if you still have difficulty bending your thoracic spine backwards, a useful visualization that I've heard teachers use is to "focus on drawing the thoracic spine towards the front of the body." At the same time you can focus on lifting and opening the front of your chest.
So that the thoracic back bend is even on both sides try to make both sides of the back of your ribcage feel the same.
You may have to slightly twist or wiggle your ribs in order to make this happen. And you may have to work towards it over several practice sessions.
You can try to activate the lumbar spinal erectors using a similar visualization. However for this to work you may have to activate your abs first. Then you can draw your lumbar spine "into your body" while at the same time bending it backwards. Here again feel both sides of the back of your lumbar region and try to make both sides feel the same.
Whether you focus on opening the front of the body or "tightening" or "engaging" the back of the body, in back bending yoga poses, focus on making your spine (and legs and arms) feel long.
Puppy dog is similiar to upward dog in that it is easy in both of these belly down backbending poses to relax the spinal erectors.
In upward dog the arms are used to lift the ribcage and bend the body backwards. In puppy dog the knees are use to lift the hips and bend the spine backwards from the bottom end.
Here too it is easy to just relax the spinal erectors and let gravity do the work of bending the spine backwards.
I'd suggest for these poses, because it is more difficult, first learn to activate the spinal erectors. You can then control your lumbar spine and thoracic spine and choose where the bend happens. Once you are more comfortable with activating your spinal erectors, then you can experiment with relaxing them and noticing how the pose feels. You can then choose based on the feeling of the pose as opposed to being too lazy to activate the spinal erectors.
Another option, is to slowly activate your spinal erectors and then relax them. You can do this in either pose. This can be used to train your ability to contract and relax your spinal erectors, and you may find that smoothly activating and relaxing allows you to gradually deepen the pose.
To enter Puppy dog Junior, start in cat pose. Reach your pubic bone back between your legs and your sacrum forwards so that your pelvis tilts forwards. You could also focus on reaching the back of your butt muscles upwards. As you tilt your pelvis forwards allow your lumbar spine to bend backwards. Slowly bend your elbows to sink your chest to the floor and bend your thoracic spine backwards also.
So that your chest can touch the floor move your chest and pelvis forwards and down so that your pelvis is slightly (or alot) ahead of your pelvis.
With your chest on the floor you can gradually scoot your chest closer to your knees as you deepen your spinal back bend.
You could also add a back bend for the shoulders in Puppy dog by reaching your arms forwards.
Another prone back bending yoga pose where it is relatively easy to practice relaxing and then contracting the spinal erectors is cat pose.
In this pose it can be easy to let gravity do the work and so I generally use this pose only after my students have a feeling for activating the spinal erectors.
In this pose because both ends of the spine are supported by either the arms or legs it's easy to let gravity pull down on the ribcage and belly.
You could think of this as a combined version of upward dog and puppy dog.
In the back bending yoga poses that follow, the legs are lifted bending the hips backwards. To bend the hips backwards squeeze the buttock and hamstrings of the lifted leg. Locust pose has already been covered.
Double Leg Locust
For double leg locust, focus on pressing the pelvis down. With the hands tucked under the pelvis, push the pelvis down into the hands and then lift the legs. You may find that the more you press down, the easier it is to lift up.
For extended cat pose (left above) and warrior 3 (right above) tilt the pelvis forwards first. You can bend the lumbar and thoracic spine backwards at the same time.
The more you tilt your pelvis forwards the easier it is to lift the leg higher. To lift the leg higher contract the buttocks (gluteus maximus) and hamstrings. Or let the outer thigh hang down and focus on pulling up on the inner knee to activate the long head of adductor magnus.
hen contract your spinal erectors to bend your lumbar spine and thoracic spine backwards.
Then keep the spinal erectors activated and use the buttock and hamstring of the lifted leg to lift the leg higher.
Tilting the pelvis forwards emphasizes the spinal back bend. Engage the buttock and back of the thigh bends the hip backwards.
In all of these, work at making your spine and leg long first. Then focus on the back bend.
To lengthen the leg reach the knee away from the hip, straighten the knee and then straighten the front of the ankle (or push back through the heel if ankle is flexed.)
In the backbending yoga poses that follow, one or both legs are back with the back knee straight and the foot (or feet) on the floor.
The top of the floot can be flat on the floor or it can be lifted with the toes tucked under.
For upward dog straighten the knees and then press the feet down into the floor. You may find that this causes the pelvis to lift. To counter act this imagine lifting the thighs. You may find that the backs of your thighs engage.
In this version of Upright Pigeon, the toes of my back foot are tucked under. To back bend the hip lift the knee and so that the pelvis moves down (stretching the front of the hip) activate the back of the thigh as if trying to lift the thigh relative to the pelvis. This should help your pelvis to sink down.
In this picture of High Lunge the top of my back foot is flat on the floor. The toes could be tucked under though. Press the foot into the floor to help straighten the knee. Then to sink the pelvis focus on moving the thigh up relative to the pelvis to help the pelvis sink down.
To turn this into a spinal back bending yoga pose you can bend the spine backwards also.
Experiment with bending the spine backwards first and then lifting the knee and then vice versa. See which one is easier. Which one makes it easier to back bend deeper?
Front to back splits can be considered a back bend for the back leg. It can also be thought of as a spinal back bending yoga pose if the torso is upright and the spine bent backwards.
To focus on the rear leg, use the same technique as in the previous back bending yoga poses. Press the foot down (toes could be tucked forwards.) Lift the knee (or imagine it lifting) and activate the back of the thigh and the gluteus maximus.
Note that in splits it can be easy to not press the back leg down. Even if you are only working towards splits, you can still work at activating your back leg and spinal erectors. In this case, the more you "lift" the back leg, the deeper you can go since lifting the back leg has the effect of helping the pelvis sink down.
Reverse plank (first picture to right) is similiar to the previous group of back bending yoga poses, except that the body faces upwards as opposed to downwards.
This could be thought of as reverse locust (or reverse double leg locust.) The main difference, apart from the fact that this is belly up as opposed to belly down, is the use of the arms to support the body.
This pose can be very uncomfortable and one of the keys to make it easier is using the arms. Friction the hands forwards, towards the feet, so that the fronts of the arms are active and so that the shoulders feel like they are moving back away from the feet.
(You could also add an external arm rotation.)
Prior to lifting up into this pose, you can bend your spine backwards. Then use the shoulders to lift the ribcage. (add the external arm rotation here.) Then press the heels down and squeeze the back of the legs to lift the pelvis. Experiment with squeezing the buttocks also.
Rather than aiming to touch the toes to the floor, work at gradually increasing the height of your pelvis. Then work at reaching the fronts of your feet down.
Upward facing backbending yoga poses with knees bent and feet on the floor include table top, bridge pose and wheel pose.
For all of these backward bending yoga poses you can experiment with moving the sacrum forwards (towards the knees) or backwards (away from the knees) so that you focus the backward bend on the hips (while moving the sacrum forwards) or on the lumbar spine (moving the sacrum backwards.) In this case the sacrum is used as a reference for tilting the pelvis forwards and backwards.
In Table Top Yoga Pose press the feet down to lift the pelvis higher. You could also focus on squeezing the buttocks.
One option in Bridge Yoga Pose is to bend the elbows with forearms vertical. Press the elbows down to help lift and open the chest.
In all of these back bending yoga poses, you could bend your spine backwards by tilting your pelvis forwards so that your pubic bone moves towards your knees and your sacrum moves away from the backs of your knees. This can be tricky to learn and feel. However I'd recommend taking the time to learn just so that you can better control and feel your body.
Another option in these backward bending poses is to tilt the pelvis backwards so that the pubic bone moves towards your sternum. This will open up the front of the hips.
From there, bend your lumbar spine and thoracic spine backwards (using spinal erectors) so that your shoulders (and hands) move closer to your feet.
Camel pose is but one of a few kneeling "hip lifted" back bending yoga poses.
The hands are on the floor behind you.
In this back bending yoga pose you can engage buttocks and spinal erectors. Of more interest is the feet.
The normal tendency may be to press them into the floor. This means you are using the front of the thighs and the intent then can be that of moving the pelvis forwards.
Experiment with relaxing the down pressure of the feet (assuming your hands are on the floor.) See if this allows you to push your pelvis further forwards with greater ease.
You could enter this pose by lifting the pelvis up with hands already on the floor. Or you can start with hips lifted and then lower the hands to your heels or the floor behind you.
More extreme variations of this pose include touching the head to the floor, and grabbing the knees or fronts of the thighs and then even more extreme, bending the elbows with arms "over the head" and grabbing the feet.
A similiar pose is bow pose (above right).
In this pose you grab the feet from behind.
Because you are grabbing the feet and lifting it can be easy to forget the spinal erectors and the back of the thighs. And so the challenge in this pose can be deliberately activating them and noticing how that affects the pose.
I've included these as back bending yoga poses because they stretch the quadriceps which is on the front of the body.
Prior to Reclining Hero do seated Hero pose . Then when leaning back perch the top of the head on the floor so that the spine bends backwards. This then reduces the back bend at the hip. From there you can rest your back on the floor focusing the back bend on the hip and quadriceps.
In Frog pose you press down on the feet using the arms to lift the chest and bend the spine backwards.
Press the feet upwards against the hands so that your hands have something to push against.
It's difficult to get into this pose and so a good way to warm up is to practice doing one foot at a time.
For more on back bending, particularly on how to lift the head of the floor in wheel pose check out Yoga Basics. It also includes information on back ward bending and forward bending the shoulders and also information on counterposing or balancing back bending yoga poses.
The instructions in this pdf are geared towards helping you feel and better control your body