The transverse abdominus is the most important muscle in the body! I should write that in all capitals to emphasize it more. It isn't really. All muscles are important. They all have a job, and together they make the body work. But even so the transverse abdominus is interesting. Learn to feel it and control it in relative isolation and you may find you can use it to operate your body more effectively.
One of the first exercises I learned for activating the transverse abdominus is called Agni Sara. (There are several exercises called Agni Sara).
The exercise involved pulling the belly inwards one section at a time working from the bottom upwards, then releasing the belly one section at a time working from the top downwards. Generally you start at the bottom pulling the band of belly about an inch or two above the pubic bone inwards. Then pull the next band up inwards, and so on. I focused just on the portion of the belly between the pubic bone and the belly button and I found the releasing part more challenging than the activation part. Often times I'd practice while sitting on the toilet. Somehow it was a little bit easier then, perhaps because my belly was so relaxed.
Was there any advantage to the exercise apart from being able to control my belly to a greater degree? I did tend to feel energized after doing it. But I also learned that groups of fibers of the transverse abdominus can be activated individually.
In case you didn't know, the transverse abdominus forms, for the most part, the innermost muscular layer of the abodminal wall. It wraps around the belly like a belt between the ribcage and the pelvis.
It also straps across the front openings of the pelvis and ribcage.
Tighten the belt that this muscle forms and it pulls the belly inwards. Relax it and the belly could potentially bulge outwards.
Another exercise where I learned to use the transverse abdominus was called "diaphramatic breathing". That's in quotes because there are actually a few different breathing exercises that use the respiratory diaphragm.
This basic diaphragmatic breathing exercsise involves contracting the diaphragm downwards to expand the belly outwards and cause an inhale.
Actually, it didn't expand the belly outwards, it presses downwards on the abdominal organs causing the front wall of the belly to bulge outwards. This action expands the volume of the lungs causing an inhale.
Then the reverse action was to use the transverse abdominus to pull inwards on the belly, squeezing the abdominal organs and causing them to push on the bottom of the diaphragm, pressing it upwardss into the space of the ribcage reducing lung volume and causing an exhale.
This action can be done without affecting the relationship between pelvis and ribcage. You can keep your ribcage and pelvis still relative to each other while alternately contracting the diaphragm and transverse abdominus. I'll mention in a bit how the transverse abdominus can be used to affect the relationship between ribcage and pelvis.
One cool thing to do to make diaphragmatic breathing easier to learn is to tilt the ribcage forwards so that the sternum moves closer to the pubic bone. This reduces tension in the rectus abdominus muscle (the "six pack" muscle) and obliques making it easier to expand the belly.
Then once the feeling of activating (and then relaxing the diaphragm) has been achieved, you can incrementally lift/tilt-back the ribcage (and lengthen the belly) to add gradually more tension to the abs. With the front of the ribcage lifted (so that the rectus abdominus is lengthened) the diaphragm not only has to work against transverse abdominus tension but also against rectus abdominus tension. So if you want a more relaxed diaphragmatic breath, don't lift your chest so much!
Now I said that in diaphragmatic breathing the transverse abdominus and respiratory diaphragm take turns activating but that's probably not quite true. What actually may happen is that one gradually activates while the other gradually relaxes so that there is a smooth transition between one muscle activating and the other relaxing.
And so this offers two different ways of focusing your awareness. You could focus on your transverse abdominus, gradually relaxing it to expand your belly and gradually contracting it to pull your belly inwards. Or focus your awareness of your respiratory diaphragm. In either case work at making both the activation and relaxation phases smooth.
I've said how tilting the ribcage forwards or backwards relative to the pelviscan slacken or add tension to the rectus abdominus (and obliques). One of the ways in which the transverse abdominus can be used is to vary tension on the abdominus rectus without requiring a change in relationship between ribcage and pelvis.
That may be one of the reasons why groups of fibers can be activated independently.
For example, you could add tension to the lower fibers of the transverse abdominus. Then while inhaling using the diaphragm you can allow the portion of belly above the belly button to expand. Or, starting with your chest bent forwards, first pull in the lower belly, then as you contract your diaphragm, use the contraction to partially expand the upper belly, but also to lift the front of the ribcage.
I mentioned previously that the transverse abdominus can be used in such a way that it doesn't affect the relationship between ribcage and pelvis. Another version of diaphragmatic breathing is to activate and relax the diaphragm and TA simultaneously.
Adding tension to both muscles at the same time, the respiratory diaphragm pushes down on abdominal organs, which because the TA is engaged can't bulge forwards. This then causes the diaphragm to create an upward push on the ribcage, pushing it up away from the pelvis. The effect is like a hydraulic piston. You could activate the TA first and then activate the diaphragm or activate the diaphragm first and then the TA. In this latter case, you could let the belly bulge outwards as you activate your respiratory diaphragm, then contract the transverse abdominus while keeping the diaphragm engaged so that the ribcage lifts.
With better tension control you could use this same action to expand lumbar spine. This is often termed reverse breathing, probably because instead of breathing into the front of the belly the feeling is that you are breathing into your lower back. For this exercise, engage your transverse abdominus first. Then engage your diaphragm. While doing so use either your obliques or rectus abdominus (or a combination of both) to keep the front of your ribcage stationary relative to the front of your pelvis. Allow instead your lower back to expand. You may find your lower back on either side of your lumbar spine feels like it is expanding. And/or you may feel your lumbar spine gradually straightening (assuming that it had a backward-bend/lordosis at the start of the activation).
Now in terms of the feeling of breath, why does it feel like you are breathing into your belly or your lower back when breathing using your diaphragm? Because muscles are being used and/or stretched. Using the diaphragm to expand your belly you stretch the abdominal muscles causing sensations which make it feel like you are breathing into your belly. Likewise breathing into your lower back you create tension or stretch in your lower back, possibly in the Quadratus Lumborum muscle, which creates the feeling of breathing into your lower back.
With directed awareness you can learn to feel the contraction of your diaphragm and so better control it.
Apart from opposing the diaphragm, the transverse abdominus can play a role in stabilzing the sacroiliac joints, lumbar spine and lower thoracic spine. It helps in this case to divide the Tranverse Abdominus into three parts. This isn't to say that it consists of three parts. It is a temporary model to use to help understand TA and how it can work. It's an aid to understanding. It's one aspect of the whole, a focused point of view, but only one. For complete understanding we need multiple points of view.
But anyway, dividing the TA into three parts, those three parts attach to the pelvis, the lumbar spine and the ribcage.
The part of the Transverse Abdominus that attaches to the pelvis attaches to the points of the hips, called the ASICs or Anterior Superior Iliac Crests, and the lines that mark the border between the belly and the inner thighs, the inguinal ligaments. To understand how this lower portion of the transverse abdominus works it helps to model the pelvis as having two halves that hinge at the pubic bone and SI Joints. Pulling inwards on the ASICS causes the two halves of the pelvis to hinge so that the sitting bones or Ischial Tuberosities (ITs) move away from each other. Doing the opposite movement, causing the ITs to move inwards causes the hip bones to hinge so that the ASICS move away from each other.
The Transverse abdominus can be used to pull inwards on the ASICS causing the sitting bones to spread apart. Meanwhile the pelvic floor muscles can be used to pull inwards on the ITs causing the ASICs to spread apart.
When the lower Transverse Abdominus activates the pelvic floor muscles also activate to help control the distortion of the pelvis in much the same way the triceps activate to oppose the biceps when flexing the biceps. The action of the biceps and triceps stabilizes the elbow joint. In the case of dual activaiton of the lower transverse abdominus and pelvic floor muscles, the joints that are stabilized are the sacroiliac joints that joint the hip bones and the sacrum.
It's for this reason that some yoga teachers suggest activating mula bandha to create uddayana bandha. Activating the pelvic floor muslces can cause the lower transverse abdominus to activate just as activating the lower transverse abdominus can cause the pelvic floor muscles to activate.
A simple way to activate the pelvic floor muscles is to create an inwards pull on the sitting bones. But pull the tailbone towards your pubic bone first.
Since the pelvis hinges (sort of) at the SI joint, this dual action of the Lower transverse abdominus and Pelvic Floor Muscles helps to stabilize the SI joint. However, hip muscles also cross the SI joint (gluteus maximus, piriformis) and indirectly affect it by and so SI stability can also be created by (and affected by) hip muscle action. Additionaly hip muscles that can affect SI joint tension include the obturator internus and the iliacus muscles, both of which have a large area of attachment along the inner surface of the hip bones.
Part of what resists the action of the transverse abdominus at the back of the sacrum is a layer of connective tissue called the Thoracolumbar Composite. This is a fused mass of connective tissue made up of layers from the erector spinae aponeurosis and various other layers of the thoracolumbar fascia. This fascia connects to both sides of the back of the pelvis on either side of the sacrum. When the Transverse Abdominis engages, the Thoracolumbar combosite resists the back of the pelvis being pulled apart. The ischial tuberosities spread apart instead.
The thoracolumbar combosite forms a pocket with the back of the sacrum. The spinal erectors, and the smaller posterior spinal muslces like multifidus are sandwiched within this pocket between the back of the sacrum and the thoracolumbar composite. Some fasicles of the multifidus attach to the front surface of this layer of fascia and so when tension is added to this fascia by the action of the lower transverse abdominus these same muscles have a firm foundation from which to activate on the spinous processes of the lumbar vertebrae to which they attach.
The middle portion of TA attaches to the bits of bone that stick out the sides of the lumbar vertebrae, the transverse processes. At its attachment to the spine the TA is mostly connective tissue and this tissue forms part of the sheath that surrounds the spinal erector and smaller rear spinal muscles called collectively the paraspinalis. The sheaf itself is called the Paraspinalis Rectinalicular Sheath or PRS. Adding tension to the TA adds tension to the sheath which in turn squeezes the paraspinalis.
The connective tissue or aponeurosis of the transverse abdominus also passes behind the Quadratus Lumborum.
The QL attaches to the back of the pelvis and from there its fibers reach up to attach to the transvers processes of the lubmar vertebrae and the lowest pair of ribs (the 12th pair). A second layer of this muscle also sometimes exists and has fibers in the opposite direction reaching down from the lowest pair of ribs to attach to the lumbar vertebrae.
I had the thought, while trying to draw the QL and TA that tension in the TA could cause tension in the QL. I don't know if there is give in this portion of the TA to add tension to the QL but at the very least tension in the TA could act as a signal to the QL to activate or relax as required.
Since the lower transverse abdominus is resisted by the Pelvic Floor muscles it makes sense that some muscle resists the action of the Middle transverse abdominus. Since both the TA and QL attach to the transverse processes of the lumbar vertebrate it seems reasonable to expect that the QL might activate along with the middle fibers of the TA.
Another muscle that also has attachments to these points is the psoas. And so the middle transverse abdominus could act in concert with either the QL or the Psoas. It would depend, since the Psoas crosses the Hip joint, one what is happening at the hip joint.
I never gave much thought to the upper transverse abdominus until some experiences in a qi gong class and some pain at the junction of my thoracic and lumbar spine during forward bends.
I felt pain in the region of T12/L1 in forward bends, particularly when I wasn't focusing on lengthening my spine or on using my arms. Why didn't I just lengthen my spine and reach with my arms? Because I wanted the option not to have to do that.
And thus I started to explore the Serratus posterior inferior, a set of muscles that reaches down from the lower three or four ribs to attach to the bone that protudes from the back of the lower thoracic and upper lumbar vertebrae, the spinous process.
I found that I could activate this muscle (with a reasonable degree of surety) with a combination of first lifting the backs of the ribs and then creating a downward pull on the lower three ribs. In the process of experimenting with this I discovered that it caused the upper band of the transverse abdominus to activate.
This was important in the Qi Gong class I attend since I then found it easier to take impacts to the solar plexus.
And so just like the lower transverse abdominus working against the pelvic floor muscles, the middle band acting against the QL the upper band seems to work against the Serratus Posterior Inferior.
For those interested in the shape of muscles, it may be interesting to note that the pelvic floor muscles form a fan shape with the fan originating at the tailbone. The quadratus lumborum forms an upward pointing chevron pattern, and if the secon layer is present, also a downwards pointing chevron. The serratus posterior inferior also forms a dowwnards pointing chevron.
Perhaps even before I started experimenting with Agni Sara I remember walking to a coffee shop and having the insite that if the transverse abdominus is used to pull inwards on the waist, the obliques don't have to perform this function. They can then be used to twist (in combination with the intercostals) the ribcage or resist twisting. An idea that I believe is important in this regard is optimal muscle length. There is a length range within which muscles function well. As the relationship between pelvis and ribcage is changed, either by external action, say using the arms to drive a twist, or internal action, using the obliqeus to drive the twist, at some point the muscles may stretch beyond their effective length. Varying tension between the transverse abdominus and diaphragm to either bulge the belly or pull it inwards can vary the tension of the obliques making it easier or more difficult to continue to twist.
And so an important idea that builds up on this is learning to feel changes in muscle tension so that you can vary that tension accordingly.
And so here the idea of, say, learning to activate muscles in isolation isn't necessarily to control them, but so that you can learn to feel them, and recognize when they are or are not active, and so that you can add or reduce tension at will.
While it may be helpful to learn to activate these muscles in isolation, particularly if you are experiencing back or si joint pain, it may help to have a mroe general action that causes these muscles to activate automatically as required. One simple action is to lenghten your lumbar spine. The idea of lenghtening, or making the lumbar spine feel long is to give the spine sensation.
Muscles activating (and then relaxing) cause sensation. But that means that there is also tension, good tension, tension that gives your spine sensation and responsiveness. With practice the amount of sensation you add can be varied. It can be realtively easy (I think but take this with a grain of salt) to recognize when there is too much tension. It feels uncomfortable. But it also becomes easier to recognize the absense of tension that gives sensation. This isn't a bad thing either. It's like a bowperson who strings their bow when they want to use it but then takes the string of when they aren't intending to fire. But if they want to be ready then they keep the bow stringed.
And so the lesson here can be get used to maintaining tension while doing exercise, but know how to release that tension for rest. And learn to move in such a way that you can keep the tension.