I guess I should have known you'd ask that, so I've listed some reasons that (in my mind) yoga helps back pain, here goes:  

1.  Posture.  In our yoga practice we are encouraged to stand and sit up straighter, moving the back into its natural alignment,  Many times a simple adjustment to posture, while uncomfortable at first, will work to alleviate back pain.  

2.  What about posture makes our back hurt?  Many of us have a habit of standing with thighs thrust forward and shoulders slumped.  The thighs moving towards the front plane of the body causes several things to happen:  (1) the femurs pull ever so slightly out of the hip socket, causing irritation as the bones rub in the hip joint; the ligaments will also stretch unnaturally.  (2) When the thighs move forward, the pelvis tips (picture a bucket that should be sitting upright; with thighs forward it tips towards the back body and spills its contents over the back of the legs).  What does this do?  It compromises the natural curve of the lumbar spine.  Instead of curving in slightly, the back becomes straight in the lumbar region or - worse - curves unnaturally.  This puts pressure on the front side of the vertebral discs (small pillow shaped pieces of cartilage that buffer our vertebrae from one another).  When pinched on one side or another, these discs bulge out the other sides, press on nerves causing pain; even can rupture, sending cartilaginous fluid out to further irritate the nerves around the spine = more pain. (3) With thighs thrust forward, the hamstrings tighten -- tight hamstrings are a big factor in many cases of low back discomfort.  

All this to say, a naturally curved spine is a healthy spine.  

People who suffer with lower back pain often tuck their tailbone, thinking that curving the back (unnaturally) will stretch the back and make it feel better.  It actually makes everything just a bit worse.  Better to experience a bit of 'weird feeling' and re-enliven the lumbar curve.  One thing about the body -- once it finds its optimal position, it will go there as often as we let it.  (that's a key phrase "as often as we let it").

3.  Yoga will offer movement to strengthen the muscles that support the spine.  How?  The folding, twisting, and lengthening we do while in yoga postures will move the muscles that our traditional sit-ups don't affect.  The perfect six-pack is not doing much to protect our spine.  It's the obliques and deep abdominal muscles that need the work.  Yoga gets in there, ever so subtly.   This movement also gently massages the cartilage in our spine, kind of a 'sponge' effect - squeezing the cartilage and allowing it to absorb nourishing fluid. 

4.  As we move up the spine, we can encounter discomfort through the thoracic region, as well.  Many times this is also related to muscle weakness.  People will often get fatigued through their back through the chest region.  Look around at your co-workers -- how many stand with shoulders dropped, chest a bit concave?  The work I've described above will help, because once you take your thighs back to their natural position, the rest of the spine is set to line up more optimally.   The next step is to create length from hips to armpits; shoulders will lift, then move them toward the back plane of the body. Strengthening the muscles that hold our shoulder blades in place will aid in the posture through the shoulders.  It's not easy work.  However, once we get the shoulders lifted, shoulder blades on the back and stand with our chest lifted slightly, the fatigue goes away because, once again, we've aligned the spine as it's meant to be.

5.  Of the curves in the spine, the cervical area is the weakest.  Our head is heavy and supported by 7 very small vertebrae and the muscles surrounding them.  In my classes, I teach students movements that will strengthen the muscles at the back of the neck - often overlooked.  These movements, if done regularly, will strengthen muscles and discourage the forward thrust of the neck (which we encourage while working at computers, reading, etc.).

6.  The emotional side of back pain is a big factor.  Many people identify with their injuries -- I sat in a waiting room once and the gentleman next to me began a conversation.  It went like this:  

"Do you like your computer?  My wife would like to get an Apple also.  I have severe back pain.  It's caused by a ruptured disc in my lower back.  I've had surgery . . . . (and so on, for about 5 minutes)."  

I had not asked him about his back and - since we were sitting in a beauty shop - there was no reason for me to be talking about his health.  It just so consumed his attention, that this man now identified with the pain.  If the pain goes away, what happens to his identity?   

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