Read more about one way to define the low back, plus a fairly detailed overview of actions of the lower back and muscles that act on it, in anatomy of the lower back.
What are the muscles that act on the lower back?
Muscles that act on the lower back can include the muscles that directly attach to the lumbar spine. They can also include muscles that cross the lumbar spine without connecting to the lumbar vertebrae. Muscles from both sets are all listed in Lower back muscles
Whether dealing with low back pain, or simply trying to use your lower back more effectively, one of the first best things that you can do is create stability for your lower back muscles.
There are a few options for creating stability for the lower back. One of the most basic is that of stabilizing the hip bones. An even better idea is learning to stabilize the hip bones individually. And that's what's covered in standing hip exercises
For a bit more on the anatomy behind stabilizing the lower back, in particular how and why you might want to stabilize the hip bones, you can find out more in Anatomy and biomechanics of low back stability.
How do you stabilize the lumbar spine in spinal back bends?
One general tip you'll hear about the lower back, particularly in the context of spinal back bends, is to not focus on bending it backwards. That can be a bit hard to do since it is a part of the spine that is most amenable to back bending.
So rather than trying to not bend at the lumbar spine, one possible approach to Spinal back bending exercises is to focus on feeling your spine. And actually, what you are feeling is the muscles that act on your spine.
If you can feel them, that means that they are active, and in general that means that they are working to help stabilize your spine. And that's a good thing. Especially in Spinal back bending exercises and actions, and also in any other actions that involve the spine.
There is a lot of overlap (and confusion) between the hip joint and the lower back. One muscle that works on both is the psoas.
With respect to the lumbar spine the psoas could be thought of as a stabilizer. The difficulty with the psoas is feeling it. And so perhaps one of the easiest ways to feel the psoas is indirectly via muscles that oppose it. It's the opposition to the psoas that helps the psoas to stabilize the lumbar spine.
Straight leg sit ups are fine!
One of the myths about the psoas is that you shouldn't do straight leg sit ups because of the shear force it exerts on the lumbar spine.
In psoas anatomy you can read about how that generally isn't the case. You can also learn the points of attachment of the psoas to the lumbar vertebrae and lowermost thoracic vertebrae.
Note, just because I say that straight leg sit ups are generally fine, it doesn't mean that you should just jump in and do them, particularly if you've not been doing exercise for a while or you already have low back pain!
Approach straight leg sit ups slowly and smoothly and gradually, and if you notice pain in you lower back, then stop.
Figure out what you need to train so that you can do straight leg sits ups without pain.
How the psoas and Kidneys relate (thanks Richard Freeman!)
An interesting relationship that I learned about in a Richard Freeman workshop is that between the psoas, the lowest pair of ribs (the 12th ribs) and the kidneys. Understanding this relationship makes it easier to learn how to lengthen the low back and even provides a way of stretching the psoas. Find out more in psoas Major anatomy
Figuring out why your psoas is tight
Stretching the psoas (why it's tight and what you can do about it) takes you through an exploration of the psoas while standing and offers some explanations for why your psoas might be tight (and what you can do about it instead of just stretching it.)
All of that and more inStretching the psoas
How you can use your psoas in forward bends, back bends and spinal twists
Psoas muscle includes a lot of practical tips for using the psoas in various yoga poses, mainly forward bends, back bends and spinal twists.
Release your psoas by stabilizing your hip bone
As for releasing the psoas, Psoas release talks about the differences between stabilizing the core versus stabilizing the hip bone. To release the psoas, the suggestion here is to stabilize the hip bone. And it includes a detailed description of how to do that while standing.
Learn how to activate your psoas
Want to learn how to feel your psoas (and control it)? The psoas includes an exercise for that. It's actually an exercise for activating your psoas, but if you can activate it, you can also learn to feel it. It also offers some speculation on how the psoas might self-adjust to give itself the necessary length or room to activate effectively.
In terms of understanding the lower back, one structure that can help in this understanding is the Thoracolumbar fascia.
This structure covers the back of the sacrum and blends with the Sacrotuberous ligament on both sides.
Extending upwards from the sacrum, it ties together the backs of the hip bones as well as a large portion of the muscles that cross the lumbar spine. It acts on the back of the ribcage and even touches on the cervical spine, the part of the spine that makes up the neck.
Muscles that make up the thoracolumbar fascia include the Latissimus dorsai, the Serratus posterior inferior, the multifidus and the spinal erectors.
Another major muscle that contributes to the thoracolumbar fascia is the transverse abdominis, which you can read about in the next section. Additionally, the SI joints could be thought of as a part of the thoracolumbar fascia, or else they are strongly affected by it. In any case, they are covered in the section that follows the transverse abdominis section.
The transverse abdominis is a belt like muscle that could be thought of as a natural border between muscles that act on the front of the lumbar spine and those that act on the back of the lumbar spine. I first learned to control it and fine tune my control of it using an exercise called agni sara.
For a detailed overview of the transverse abdominis you can read transverse abdominis.
This muscle is a fairly important muscle for helping to stabilize three regions of the lower back. Its lower band can help to stabilize the SI joints. Its upper band can help to stabilize the thoracolumbar junction, where the lumbar spine meets the thoracic spine and ribcage. It's middle band can help to stabilize the middle span of the lumbar spine. Read more about that in effectively activating transverse abdominis.
For different ways to exercise or train the transverse abdominis check out transverse abdominis exercises.
You can also check out transverse abdominis training
Before getting into the thoracolumbar fascia, it can help to understand the SI Joints. The SI joints tie together the sacrum and the hip bones and when working on both SI joints at the same time, you can use the transverse abdominis, the pelvic floor muscles (which includes the PC muscle and even the lumbar multifidus to help stabilize them.
For a look at how the gluteus maximus, spinal erectors, piriformis and obturator internus all can affect the SI joints, take a look at sacroiliac joint anatomy. It also includes some general tips for figuring out how to deal with SI joint pain.
For a look at all the muscles that directly attach to the sacrum and tailbone, and how to activate them, read this article about the sacrum.
As to why we might have SI joints in the first place, check out SI Joint and SI Joint stabilization.
Single SI joint Stabilization via the hip bones
For a brief look at stabilizing one SI joint at a time, check out Single SI Joint stabilization.
For a more in-depth look at single SI joint stability with lots of anatomy plus some simple movements, then please take a look at Single side SI joint stability. Yes the titles do look quite similar, but the articles are different!
Two of the main ligaments that can affect sacroiliac joint stabilization are the long dorsal ligament and the sacrotuberous ligament. Take a look at how these two ligaments can be used to help stabilize the SI joints in sacroiliac joint stabilization.
One possible way to add tension to the sacrotuberous ligament is to activate the obturator internus. This article about the sacroiliac joint was actually inspired by an article about the dangers of forward bending for the SI Joint.
Adding tension to the sacrotuberous ligament is one way of helping to stabilize the SI joint while forward bending.
For some simple exercises to practice nutation and counter-nutation of the sacrum, take a look sacroiliac joint exercises
And for a look at keeping your SI joint safe in the context of seated yoga poses, check out SI joint stability in marichyasana
One place I've experienced low back pain is near the junction of the lumbar spine and the ribcage (the thoracolumbar junction). I tended to experience this while doing yoga poses like seated forward bends, but also while doing deep squats. In any case, the solution is detailed in low back pain anatomy for yoga
Dealing with a dull but annoying ache in the lower back
This is from one of my earlier experiences of dealing with low back pain. It's a technique for "straightening" the lumbar spine using the multifidus while at the same time using the pelvic floor muscles. So this technique works on (or includes) the SI Joints also. Note, that even if this technique doesn't help your lower back pain, it can help to improve your awareness of your lumbar spine. Read more in low back pain.
Standing exercises for low back pain (and becoming more resistant to it)
Provided your low back pain isn't to severe, this set of standing exercises may help you develop resilience to lower back pain by helping you train among other things your gluteus maximus. I talk about why this muscle can be important for stabilizing the hip bone is anatomy of the lower back. Here you can read more about actually using your gluteus maximus, and other muscles, to give your lower back muscles a stable foundation while standing. Find out more in standing exercises for low back pain.
And on a related note, I have flat feet, or rather collapsed or fallen arches. Here's a writeup on a possible connection between the two: low back pain and fallen arches
Spinal twists for the lower back (and upper back)
One way to work on the lower back and the spine in general is to do active spinal twists. Here's a look at the anatomy of twisting (This article should be done soon.) There is some overlap here with anatomy of the lower back. However, with the anatomy of twisting we go a little further up the spine.
With twisting, we can think of the hip bones and the ribs (and the skull) as extensions of the spine. They provide leverage for the muscles to act on the spine. With active spinal twisting the idea is to learn to use those muscles to drive the twist. This is as opposed to just relying on the abs, or even the arms.
Note that because twisting uses a large portion of the muscles that act on the spine, you may find it a helpful practice for alleviating low back pain and back pain in general. But do see a doctor first if you are unsure.
Why is feeling your spine so important? Well, if you can feel it, it means that muscles are activating. For muscles to activate they need a force to work against. That can be body weight, but it can also be opposing muscles. And so in general, when you can feel your spine it is because opposing muscles are working against each other to generate the sensation that you feel. They are also working against each other to stabilize your spine.
And so feeling your spine is a general tip for stabilizing and otherwise controlling your lower back. Since the hip bones and ribs directly attach to spinal vertebrae, a large part of feeling your spine and stabilizing it includes learning to feel and control your hip bones and ribs as well as the "spine" itself.
To get a feel for your lumbar spine, hips and ribcage (they all connect and they all affect each other) as well as other basic elements, check out the muscle control for your spine course.