The Transverse Abdominis is generally considered the innermost or "deepest" abdominal muscle. It lies beneath the external and internal obliques and behind (and partially intertwined with) the rectus abdominis.
It should be noted that the Transverse abdominis passes behind the quadratus lumborum before attaching to the lumbar vertebrae.
And both the psoas and the respiratory diaphragm attach to the lumbar spine in front of the quadratus lumborum.
These muscles could therefore be considered "deeper".
The horizontal fibers of the transverse abdominis wrap around the waist between the ribcage and the pelvis like a belt.
The two halves of the muscle join in front at the linea alba and at the back they pass behind the quadratus lumborum muscle before attaching to the transverse processes of the middle lumbar vertebrae.
When activated, the transverse abdominis contracts inwards.
This muscle can be divided into three bands horizontal bands.
- The upper band attaches to the lower ribs, the ribs that form the costal arch.
- The lower band attaches to the ASICs, the points of the hip bones, and the ingiunal ligament, the ligament that forms the crease between your belly and your thighs.
- The middle band is the part that wraps around the waist beween the ribcage and the pelvis.
These three bands can be activated individually or all together!
What the transverse abdominis does depends on context. Here's the overview: Function of the Three Bands, Belly Breathing Exhales, Diaphragm Resisted Breathing, Abdominal Pressurization, Lumbar Stabilization, Tensioning Device for Obliques and Rectus Abdominis, Stronger Spinal Erector Activation, Prebracing the Abdomen, Anchoring the Serratus Anterior, Anchoring the Hip Flexors
If focusing on the indvidual bands of this muscle then:
The top part can be used to help stabilize the thoracolumbar junction, the place where the thoracic spine connects to the lumbar spine.
Here it can work in conjunction with the serratus posterior inferior and or the respiratory diaphragm.
The lower part can be used to help stabilize the SI joints, where the sacrum connects to each of the hip bones.
Here it can work in conjunction with the pelvic floor muscles and/or the sacral multifidus.
The middle part is the part that helps to pull the belly inwards towards the spine. You could think of this as the waist-thinning portion of the transverse abdominis.
This portion may work together with the quadratus lumborum, the respiratory diaphragm and or the lumbar multifidus.
In one type of belly breathing method, the diaphragm contracts downwards to cause an inhale. In doing so it causes the transverse abdominis to push outwards so that you look pregnant.
To create an exhale, you can use your transverse abdominis to pull the belly inwards which then causes the abdominal organs to press diaphragm upwards.
In another type of breathing method, the transverse abdominis can be used to resist the respiratory diaphragm. In this case the first action can be to pull the belly inwards using the transverse abdominis. Then while it is kept active, the diaphragm can then be activated to cause an inhale.
Because of the resistance of the Transverse abdominis, the contraction of the diaphragm causes the ribcage to lift and expand. This can cause the diaphragm to work harder since it is working against the weight of the ribcage, arms and head.
For the exhale, the transverse abdominis can be kept engaged so that only the diaphragm is relaxed. Or both can be relaxed together.
In a modification of this latter method, tension of the transverse abdominis can be used to resist the diaphragm to varying degrees. This can then cause the abdomen to be pressurized to varying degrees.
While abdominal pressurization can help to stabilize the core of the body, like filling a water balloon with more water, it also can stabilize the lumbar spine directly.
In this case you can view the abdominal organs provide a means for the transverse abdominis and diaphragm to work against each other.
With the transverse abdominis providing an opposing force to work against, the diaphragm can act via its attachments to the front of the lumbar spine to help stabilize it.
When the transverse abdominis pulls inwards, it pulls the other abdominal muscles with it. As a result, it can cause the front of the ribcage to pull towards the front of the pelvis causing the lumbar spine to flatten.
You could think of this as "taking out the slack" from the obliques and rectus abdominis.
These muscles can then act with less effort when the need arises.
Taking out the slack from there muscles may help to anchor the hip flexors, particularly where they attach to the ASIC and the pubic bone.
If you are in a back bend, say bridge for example, you can activate the transverse abdominis to pull the belly inwards.
Since the transverse abdominis passes behind the quadratus lumborum, in a spinal back bend (or with the spine in extension) the TA may help to add operating length to some of the fibers of the QL (particularly the outer fibers).
Since it pulls inwards on the other abdominal muscles, and assuming that they are also activate, this then gives the spinal erectors more force to work against which can lead to a stronger as well as a more sensational back bend.
Transverse abdominis activation may also lead to stronger spinal erector activation because it's connective tissue fibers form part of the tube that wraps around the lumbar portion of the spinal erectors.2
Research suggests that the transverse abdominis tends to activate in order to stabilize the torso, a prebracing action, in particular against rapid limb movement.1
One reason for this could be that it pulls in on the other abdominal muscles, removing slack and thus making them more responsive.
So for example, pulling in with the TA adds tension to the obliques, both layers, making it easier for those muscles to work against each other to stabilize ribcage and pelvis, or so that they can work quickly to turn or otherwise move your ribcage relative to your pelvis or vice versa.
A stable ribcage can work as a foundation for anchoring shoulder muscles and thus the arms arms while a stable pelvis can work as a foundation for anchoring muscles of the hips and thus the legs.
When the transverse abdominis is activated in such a way that the sternum is pulled down towards the pubic bone, then this can help to anchor the serratus anterior muscle.
With the shoulder blades anchored, say by the rhomboids, the serratus anterior can be used to pull up on the fronts of the ribs.
It then seems fairly obvious that if you want to help anchor the serratus at the ribcage, then you create a downwards pull on the ribs.
When the transverse abdominis is activated in such a way as to pull the ASICs (the points of the hip bones) upwards, or to resist them being pulled downwards, this then helps to anchor the hip flexors, in particular those that attach at or near the ASIC.
The transverse abdominus also attaches to the inguinal ligaments, under which both the psoas and iliacus pass before attaching to the inside of the thigh bone. Since the iliacus also attaches to the hip bone, lower transverse abdominis activation may help to anchor it.
To learn to feel any muscle, practice activating and relaxing it and notice the accompanying change in sensation.
To feel your transverse abdominis, pull your belly back towards your spine. Notice the sensation that occurs as you do so. Then relax and again notice the change in sensation.
Watch out for the Stomach Vacuum.
There is an exercise or action called a stomach vacuum. This involves exhaling completely, holding your breath and then pulling your ribcage upwards. This then causes your belly to suck in.
In this case you aren't activating your transverse abdominis, you are just sucking your belly in.
So a good way to avoid this (or to be able to differentiate between the two) is to learn to feel and control your ribcage.
A simple way to stretch the transverse abdominis is to use belly breathing. When inhaling, expand your belly (by pushing down with your diaphragm.) This is when you stretch the transverse abdominis. Then relax to inhale.
Work at making both actions smooth and comfortable.
So that you not only stretch your transverse abdominis but also exercise it, focus on pulling it inwards while exhaling.
You can practice stretching your transverse abdominis both with your lumbar spine bent forwards (sternum towards your pubic bone) and backwards (sternum moving away from your pubic bone).
Doing it with spine bent forwards may be easier, however, once you get the hang of it with spine bent forwards, you may find you get an increased stretch doing it with your lumbar spine bent backwards.
"Resisted" Active Stretching
For a Resisted active stretch, practice resisting both movements.
While inhaling, gently resist your belly expanding so that your diaphragm has to work harder. Then do the same while exhaling. Resist with your diaphragm so that your transverse abdominis works harder.
You may find that this gives you better control of your breathing.
All muscles are important. However the transverse abdominis is perhaps most important because it can work against the respiratory diaphragm during respiration.
It can also help to stabilize the lumbar spine. And it can be used to help take out the slack from the other abdominal muscles so that they can then work more effectively to stabilize the pelvis/lumbar spine/ribcage or control how they all relate.
To train your transverse abdominis, first practice activating and then relaxing it in isolation.
Then practice using it in various poses or actions. So that this is easier to do, practice feeling your transverse abdominis activating (and relaxing).
When using it to "flatten" (or "flex") your lumbar spine, feel both your transverse abdominis and your lumbar spine.
The first exercise is done while standing. Slowly pull your belly in. Pause. Then slowly relax your belly.
1. Transverse Abdominis relaxed.
2.Transverse Abdominis activation so that Belly is pulled in.
To begin with, focus on keeping both your ribcage and your pelvis stationary while doing this.
I'd also suggest inhaling and exhaling through your nose. When you pull your belly in, you should cause an exhale. When releasing your belly, you should find yourself inhaling.
If you want to work at holding your belly pulled in, then allow your ribcage to move as you inhale and exhale.
Standing Side Bend
You can pulling your belly in while doing a standing side bend. Here you don't have to flatten your lumbar spine. Just focus on feeling it and make any adjustments necessary so that your lumbar spine, hips and knees feel comfortable.
Try standing side bend with arms down first, it can make it easier to activate your transverse abdominis. Then when you add the arms, work at keeping it engaged.
You can try the same transverse abdominis exercise in a standing twist. With feet parallel or slightly turned out, turn your pelvis, and your ribcage and your head. Pull your belly in and see if you can deepen your twist gradually.
Once you get used to keeping your transverse abdominis engaged in the standing twist, work at lengthening your sacrum and thoracic spine to give them "feel". Use the feel to deepen your twist.
Flexing your Lumbar Spine
A variation of the first exercise is to pull your belly in and as you do so draw your sternum towards your pubic bone so that your lumbar spine "flattens". See if you can feel your lumbar spine "lengthen" or "flatten" as you do so.
Here I'm focused on pulling my ribcage down using my transverse abdominis.
When you relax, allow your ribcage to lift.
Another variation is to pull your pubic bone up as you draw your belly in. Here again pay attention to your lumbar spine and work at feeling it "straighten" as you draw your belly in.
Here I'm focused on pulling my pubic bone up while using my transverse abdominis to pull my belly inwards.
Once you've practice both exercises, use which ever method feels best depending on what you are doing at the time.
Lumbar Flexion with a Knee or Leg Lift
Building on the previous exercise (pulling up on the pubic bone), stand on one foot with the other foot in front. Pull your belly in, and your pubic bone up to flatten your lumbar spine. Keep your belly pulled in and then slowly lift your front leg.
In the starting position my weight is over my back foot!
Note that with my left lifted, my pelvis isn't level.
I'd suggest adjusting not for a level pelvis but so that both sides of your belly (and your lumbar spine) feel even.
A variation is to lift the leg with the knee straight.
Note the sartorius activation. Another "benefit" of using the transverse abdominis is it can help to anchor hip flexors like the sartorius.
Particularly when lifting the leg with the knee straight, make sure that you activate your transverse abdominis first. Then, to make it easier to keep the action, gradually lift your leg while keeping the knee straight.
The standing knee can be bent or straight!
On All Fours
On all fours you can try drawing your belly in so that again your sternum and pubic bone move closer to each other.
Once you can do this comfortably, try lifting your knees after a full contraction.
You'll have to look closely at the picture to see that my knees are actually lifted. A good test of general awareness and control is to try to lift your knees just clear off of the floor.
From all Fours to Plank
From all fours, another option is to step back to plank after having activated your transverse abdominis.
It can be difficult to activate your transverse abdominis while you are in plank. The following steps can make it easier to activate your transverse abdominis and then keep it active as you move into plank.
The steps are:
- Pull your belly in
- Protract your shoulder blades
- Keep your ribcage and pelvis still as you step one foot back at a time.
Hold for a few breaths, then release and repeat.
Step your feet back slowly, so that it is easier to keep your torso still and your transverse abdominis engaged.
Lying on your back with knees bent and hips lifted, here too you can pull your belly in to activate your transverse abdominis.
Note the sensations that occur in your lumbar spine but also at the lower "rim" of your ribcage.
With your belly pulled in you can work at lifting your hips higher or otherwise deepening your spinal backbend.
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2a. Barker PJ, Briggs CA (1999) Attachments of the posterior layer
of the lumbar fascia. Spine 24, 1757-1764.