What if a single structure could help deal with low back pain, pelvic girdle pain and SI joint instability (which could cause pelvic girdle pain)?
Because of the way that the Thoracolumbar Fascia connects the Transverse Abdominus and Spinal Erectors, it can affect lumbar stability in both extension (back-bending) of the spine and flexion (forward-bending) of the spine.
Because of the way that it binds the PSIS on each side and the rear of the sacrum it can also play a roll in stabilizing the SI joint.
Via the connections between the gluteus maximus and latissimus dorsai it can play a role in twisting of the spine and hips.
Because it connects to the sacrotuberous ligament, the biceps femoris and the sacrotuberous ligament it can play a role in extension (back-bending) of both the spine and the hips.
Understanding the thoracolumbar fascia and the muscles it connects to may also be helpful in dealing with back pain, and pelvic girdle pain.
Some bony reference points that it connects to or affects include:
While elements of the Thoracolumbar Fascia can be found along the entire length of the spine from the sacrum to the base of the skull, its interconnections seem particularly meaningful in the lumbar and sacral regions.
The Paraspinalis Rectinacular Sheaf (or PRS) is the sheaf of connective tissue that wraps around the Erector Spinae and Multifidus muscles. In the lumbar region the front wall of this connective tissue sheaf passes between the spinal erectors and quadratus lumborum to attach to the transverse processes of the lumbar spine. The connective tissue that covers the rear surface of the quadratus lumborum also connects to the PRS as it passes behind that muscle.
The Transverse Abdominus is a belt like layer of the muscles with fibers that run horizontally around the waist. It attaches to the transverse processes of the lumbar spine after first blending with the fibers of the anterior wall of the paraspinalis Rectinacular sheaf. Thus the front wall of the PRS is thicker than the posterior wall.
Some sources refer to the front wall as the MLF or the middle layer of the thoracolumbar fascia and it is a convenient term to indicate the portion of the PRS which includes fibers from the aponeurosis of the transverse abdominus muscle as well as fibers from the fascia of the quadratus lumborum.
The Transverse Abdominus creates a seam where it connects to the PRS. This seam is called the Lateral Raphe and it extends between the iliac crest and the bottom of the 12th rib (the lower most rib). This raphe marks where the MLF begins.
When activated the transverse abdominus pulls the belly inwards past the border of the ribcage and pelvis.
Before the aponeurosis (or "tendon") of the Transverse Abdominus joins with the PRS it divides into two layers with those two layers connecting to the PRS in such a way as to form a triangular shape called the Lumbar Inter Fascial Triangle or LIFT. Whether both of these layers blend with the MLF or one layer wraps around to the back of the PRS is not stated in any of the articles that I've read.
From the Lateral Raphe, the middle edge of the posterior surface of the PRS connects to the spinous processes and supraspinous ligament which runs up (and down) the rear of the spine connecting the spinous processes.
Although the rear wall of the PRS is continuous with the front wall, in some sources it is referred to as the Deep Lamina (DL) of the Posterior Layer of the Thoracolumbar Fascia (PLF).
In the lumbar region the front wall of the PRS is made up of the MLF. In the thoracic region the front wall is made up of the rear surfaces of the thoracic vertebrae and ribs and intervening fascia. The bottom edge of the MLF ends near the top of the sacrum where it fuses with the iliolumbar ligament. From then on downwards the front wall of the PRS is made up of the iliolumbar ligament and the sacroiliac joint capsule.
The rear wall of the PRS becomes fairly thin in the thoracic region. In the cervical region it becomes the investing fascia of the cervical spinal erectors which suggests that tension in the neck muscles can can cause tension in the sheath in other parts of the spine.
Passing the sacral region the rear wall of the PRS fuses with with the aponeurosis of the spinal erectors which is between it and the sacrum. It also fuses with the superficial lamina of the Posterior Layer of the thoracolumbar Fascia (PLF) which is behind it. The resulting Thoracolumbar composite also fuses to the PSIS on either side
As it drops lower it blends with the sacrotuberous ligament as well as the biceps femoris.
In the lumbar region the PRS wraps around three sets of muscles, the longissimus and iliocostalis (both erector spinae muscles) and the multifidus (part of the transversospinalis group.)
Despite being called the Erector Spinae Aponeurosis, this aponeurosis actually connects to all three muscles in the lumbar region. It's positioned to the rear of these muscles so that they all attach to its front surface.
In the lumbar region the aponeurosis is only loosely connected to the PRS which indicates that it can move within it. In the region of the sacrum it becomes fused with the PRS as well as the more rearward positioned superficial layer of the PLF.
Extending up from the sacral region the center of the spinal erector aponeurosis extends upwards into the lower part of the thoracic region. Passing the sacrum it may broaden sideways to attach to the top of the iliac crest. From there the sides of the aponeurosis only reach about as high as the bottom of the third lumbar vertebrae so that the top edge of the aponeurosis forms an upward pointing triangular shape that expands sideways to each side to about the middle of each half of the back.
The import of this is that it covers the entirety of the lumbar multifidus as well as the base of the iliocostalis and longissimus muscles.
When flexing the spine (bending it forwards) the rear wall of the PRS is lengthened vertically while at the same time it gets thinner laterally. Activating the Transverse Abdominus so that they pull inwards towards the spine, there may be a point, if enough tension is added, that a lateral pull is created on the PRS which then causes it to resist forward bending of the spine. Stretching the fascia sideways makes it try to shorten longways. Bending rearwards (extension) if the transverse abdominus are pulled inwards enough they could be used to help reduce the top to bottom length of the rear wall of the PRS thus assisting extension of the spine.
Note that in either case the transverse abdominus has to be activated with enough force to at least pull the belly inwards past the border of the ribcage.
If kept held in for more than a few seconds, then breathing can be accomplished using the respiratory diaphragm or a combination of the respiratory diaphragm, intercostals and possibly the thoracic spinal erectors.
Intra Abdominal Pressure (or IAP) can be created in front of the lumbar spine by contracting the respiratory diaphragm to presses down on the abdominal organs, contracting the pelvic diaphragm to resist the organs moving downwards and also contracting the transverse abdominus to pressurize the abdominal organs cirumferentially. The obliques and rectus abdominus can also take part in creating IAP. One reason for creating IAP is to brace the front of the spine.
The PRS surrounds the spinal erectors in such a way that when they activate the sheaf magnifies their effort. At the same time the sheaf is pressurised by the activation and becomes more resistant to back bending. And so one reason for activating the spinal erectors in a back bend (particularly in poses where gravity assists the back bend) is that the Pump Up action of the spinal erectors within the PRS helps to support or bolster the rear of the spine, reducing pressure on the rear part of the inter-vertebral discs.
In the region of the sacrum the aponeurosis of the spinal erectors fuses with the rear wall of the PRS and the superficial layer of the PLF forming what is referred to as the Thoracolumbar Composite or TLC.
(Again note that in some papers the rear wall of the PRS is referred to as the deep lamina of the PLF so that the TLC could be thought of as a fusion of the Spinal Erector Aponeurosis with both the deep and superficial laminas of the PLF. PRS is the more common term now adays since it has been determined that there is no lateral seam on the inner surface of this construct.)
The TLC connects to the PSIS at the rear of each iliac crest, to the sacrum. It also blends with the Long Dorsal Sacroiliac Ligament and the Sacrotuberous Ligament. The TLC resists any lateral spreading apart (or protraction) of the two PSIS and this resistance may be augmented by activating the lumbar multifidus since they then pump up the the TLC helping to increase it's tension and thus its resistance to protraction of the two PSIS.
In the region of the pelvis, the transverse abdominus connects to the ASIS and to the inguinal ligament which runs between the ASIS and the Pubic tubercle (close to or on the pubic bone.)
If these particular fibers of the Transverse Abdominus are activated, they can be used to pull inwards on the ASIS which then creates an outward moving force at the PSIS which relative to the ASIS are to the rear of the SI joints. Since the TLC component of the Thoracolumbar Fascia resists this movement one result is that the two surfaces of each SI joint are pressed closer together leading to increased SI joint stability.
In SI joint mechanics, an inward movement of the ASIS is generally accompanied by a forward movement of the top of the sacrum so that the upper opening of the pelvis gets larger. At the same time the bottom tip of the sacrum (the tailbone) moves forwards while the ischial tuberosities move inwards so that the bottom opening of the pelvis gets larger.
The outward movement of the ischial tuberosities (sitting bones) and rearward movement of the tailbone may be resisted by the pubococcygeus muscles. This is similiar to the act of flexing the biceps. When posing with biceps flexed the triceps also activate so that the elbow stays bent at the same angle. The biceps and triceps work against each other to effectively stabilize the elbow in the desired position. These muscles could be used against each other in any position of the elbow whether straight, or bent to 45 degrees or more or any position in between. The only time the biceps wouldn't have to work against the triceps is if they were working against some external object or force.
In the same way, if the transverse abdominus aren't working against some other force to retract the ASIS then the pelvic floor muscles will activate to stabilize the pelvis and SI joint in the desired configuration. If there is some external force that the Transverse Abdominus is working against then the pelvic floor muscles may not have to activate.
Focusing on the shape of the spine (and ignoring hip actions for the moment) one possibility is that nutation of the sacrum may best be suited to extension of the lumbar spine while counter nutation best stabilizes the SI joint when the lumbar spine is bent forwards.
(I say "possibility" because it may also depend on the position of the hips and what the hip joints are doing.)
Activating the spinal erectors to bend the spine backwards they can also be used to nutate the sacrum. The transverse abdominus can assist in this action by drawing inwards on the ASICs.
In this case the force exerted by the Transverse abdominus and spinal erectors is slightly greater than that exerted by the pelvic floor muscles.
Bending the spine forwards, spinal erector and transverse abdominus tension can be gradually ramped down while pelvic floor muscle tension is smoothly increased so that the si joint moves smoothly from nutation to counter nutation. The opposite can be done when moving from counter nutation to nutation.
In such an exercise it may be helpful to initially focus on the lower band and upper band of the transverse abdominus in isolation but then work towards a contraction of the entire transverse abdominus while at the same time contracting the complete set of lumbar spinal erectors during nutation of the sacrum and extension of the lumbar spine.
I'd also suggest learning to feel when the pelvic floor muscles are engaged and when they are relaxed. Do the same for the transverse abdominus and spinal erectors. The idea isn't to consciously control them all the time but to be able to exert conscious control when desired.
Also important is not keeping, say, the pelvic floor muscles activated all of the time. Muscles are designed to activate and relax.
While standing bend the spine rearwards. First activate spinal erectors and then activate transverse abdominus. Drop the ribcage and the tailbone so that the lumbar spine straightens and then bends forwards. (It can feel like you are opening the back of your lumbar spine.) At the same time activate the pelvic floor muscles by drawing the tailbone towards the pubic bone and drawing the Ischial tuberosities inwards. Then tilt the pelvis forwards to return to the start, activating the spinal erectors and increasing the action of the transverse abdominus.
In isolation you may find it helpful to focus on drawing the ASISs towards each other. Then practice drawing the ASIS and inguinal ligaments inwards towards each other. Then practice drawing inwards on the entire belly. You may find this action helpful when doing spinal twists.
In the lumbar region the transverse abdominus attaches to the sides of the lumbar spine. In the sacral region the pelvis acts as an intermediary between the transverse abdominus and the sacrum. At the level of the pelvis and sacrum the transverse abdominus attaches to the ASIS and the inguinal ligament. When this portion of the TA contracts it creates an outward pull on the PSIS that the Thoracolumbar composite resists This in turn may partially compress the Multifidus possibly increasing their effective output force.
When the transverse abdominus at the level of the lumbar spine contracts the PRS in this area may also be compressed again resulting in increased output of the spinal erectors there.
If a focus on the SI joints and nutating the sacrum is desired it may be helpful to practice activating the transverse abdominus at the level of the PSIS. If the focus is on both the lumbar spine and the sacrum then focus on activating this level of the transverse abdominus as well as the fibers that attach to the lumbar spine.
The thoracolumbar fascia can play an large roll in facilitating twisting and to that end it may be helpful to focus on activating the transverse abdominus fibers that connect to the inguinal ligaments.
The external obliques and internal obliques both partially attach to or help to form the inguinal ligaments and pulling inwards on the ligaments to add tension to them via the TA may give the both sets of obliques an extra large foundation from which to work on helping to twist the ribcage.
In the book Anatomy Trains Tom Myers notes that the biceps femoris can be relatively easily detached from its attachment to the Ischial Tuberosity. It then relies on the sacrotuberous ligament as its upper point of attachment. In several papers it is noted that the fibers of the biceps femoris (long head) either partially or completely run into those of the sacrotuberous ligament. While the other hamstrings, the Semi-Tendinosus and Semi-Membranosus also connected with the thoracolumbar composite the biceps are noteworthy in this.
A main difference in the muscles of the hamstrings is that the Biceps Femoris long head and short head both attach to the top of the fibula, the smaller and outermost (most lateral) of the two lower leg bones. The short head of the biceps femoris originates from the back of the femur.
The Semi-Membranosus, perhaps the deepest of the hamstrings, attaches to the rear and medial portion of the tibia just below the knee. It is sheetlike in appearance being wide in breath but thin in depth and may be important in adding tension to the inner portion of the knee capsule.
The Semi-Tendinous is thin and tendon-like for almost half its length with the bulk of the belly of the muscle located more towards the sitting bone end of the muscle. It attaches lower on the tibia than the Semi-Membranosus joining with three other long and thin muscles, the Gracilis (which attaches close to the pubic bone) and the Sartorius (which attaches close to the ASIS.)
Meanwhile, fibers of the Gluteus Maximus attach to the fibula via the Iliotibial Band (or Iliotibial Tract) and fibers of the Tensor Fascae Latae also attaches to the fibula via the same band of connective tissue. The Tensor Fascae Latae also attaches to the ASIS like the aforementioned sartorius.
And so it may be that the two groups of hamstring muscles (and the muscles associated with them) are designed to work under different circumstances or as parts of two different sub-systems:
These two subsystems could work individually according to circumstance or they could also work together.
Moving into or out of a forward bend, the inner hamstring set (Semi-Membranosus and Semi-Tendinosus) could help to stabilize and control the knee, hip joint and pelvis while the outer hamstrings (Biceps Femoris) help control the spinal erectors, giving them a stable foundation from which to work on the back of the spine.
Working together to control both the pelvis and the sacrum, the two sets of muscles could help to reduce shearing forces on the SI Joint. While the biceps femoris could pull caudalwards (away from the skull) on the sacrum the Semi-Tendinosus and Semi-Membranosus could create a caudalwards pull on the ischial tuberosities thus balancing the pull across the SI Joint by pulling equally on the pelvis and sacrum.
The upsight of this is that to reduce sacroiliac wear and tear it could be worthwhile developing control of the entire set of hamstring muscles as well as awareness so that you can learn to feel whether the outer or inner hamstrings are activating and whether or not the short head of the biceps femoris is activated or not.
In the two layer model of the thoracolumbar fascia, the Latissimus Dorsai and Gluteus Maximus are both part of the superficial lamina of the TLF's posterior layer.
The biceps femoris, spinal erectors and serratus posterior inferior are part of the deep layer.
While other muscles do connect to these layers the aforementioned muscles are important because it has been shown that they can affect each other via the thoracolumbar fascia. An experiment involved pulling on different muscles to see how the thoracolumbar fascia was affected and these muscles had the greatest effect.
One dissection (unrelated to the above experiment) involved removing the gluteus maximus completely while leaving the thoracolumbar composite intact and what this indicated to me is that while the gluteus maximus isn't considered a part of the deep layer, it connects to the deep layer and can be deeply affected by it.
(In all specimens parts of the fascia of the gluteus maximus are continuous with the superficial lamina while the deep fascia and the muscle itself show multiple connections with the sacrotuberous ligament. It also connects to the long ligament.)
As an example, tension applied to the thoracolumbar composite (perhaps caused by the biceps femoris activating and/or the erector spinae) could give the gluteus maximus a stable foundation from which to pull on the femur or via the iliotibial band, on the fibula (so why if it connects to the fibula is the band called the ilio-"tibial" band?).
Another way to look at the thoracolumbar composite is that it acts as a communication medium. Not only does it potentially give the gluteus maximus or spinal erectors (and possibly the biceps femoris) a stable foundation from which to activate, it could also be thought of as a communication device telling each of the muscles which other of those muscles are currently active and which aren't.
As mentioned the Gluteus Maximus has a connection to the lower fibers of the opposite Latissimus Dorsai. The Latissimus Dorsai has connections to the spinous processes from L3 or L4 (below that its fibers cross the center line to the opposite side PSIS and glute) upwards to about T5 or T6 as well as to the lower ribs and the lower part of the lateral raphe, just above where it connects to the iliac spine.
Before it connects to the upper arm bone its tendon is twisted so that the fibers that attach lower on the spine attach higher up on the arm (if the arm is down.) The twist is taken out when the arm is lifted above the head. One fancy of mine is that the fibers that attach to the gluteus maximus, when activated also signal (and perhaps create a foundation for) the other fibers to activate.
So we now have the Biceps femoris which attaches to the spinal erectors via the thoracolumbar composite and deep layer of the thoracolumbar fascia. Then we have the Gluteus Maximus connecting to the arms via the Latissimus Dorsai and the superficial layer of the TLF.
The glutes could activate and act as a foundation from which the lower fibers of the lats can act on the arms. Or the lats can activate and give the gluteus maximus a foundation from which to act on the legs.
Either action could assist the biceps femoris and spinal erectors in bending the spine and hips backwards causing extension of both.
In addition, since we as humans have hands and are possibly designed to pick things up, this gives one possible mechanism for picking things up while bent forwards.
The inner hamstrings could control and help to stabilize the knees and hips and pelvis. Meanwhile the outer hamstrings help to give the spinal erectors a stable base from which to act on the rear of the spine. This in turn gives the glutes a foundation from which to anchor the lats which in turn then can act on the arms while at the same time supporting the back of the lower half of the ribcage and spine.
And it should be noted here that the lower half of the ribcage is the more flexible and less stable part of the ribcage. In the upper part of the ribcage the ribs all attach to the sternum making this part more stable but less flexible.
It could be worth mentioning that in the lumbar region the transverse abdominus attach to the sides of the PRS and thus when activated create a sideways pull on the PRS thus resisting flexion and helping to create flexion. But also this tightens the container of the paraspinalis and amplifies their contractive effort. It may also be possible, since in the thoracic region the rear face of the PRS is fairly thin, that activation of the lats squeeze the spinal erectors between the themselves and the rear of the thoracic spine and ribcage thus again possibly amplifying the action of the spinal erectors.
Whether this latter part is true of far fetched fantasy, the important points are that the hamstrings, spinal erectors, and lats can all work together while back bending or coming out of a forward bend (or while going into a forward bend under control.)
And one action that may be useful, then, when going into a forward bend or coming out of one, particularly a deep one, is to activate the lats even if you aren't picking up or lowering weight.
And of course also activate the hamstrings and the glutes. This then not only supports the spine but also potentially balances tension across the SI joint by acting on the sacrum as well as the pelvis.
One final point about the glutes and lats is that the opposite side Gluteus Maximus and Latissimus Dorsai could be useful in twisting. Twisting to the right the left Glute could be activated to push forwards on the left side of the hip. Meanwhile the right side of the ribcage could be pulled back with the help of the right side lat.
One action this could be useful during is throwing. For a right handed throw the pelvis and torso could be twisted to the left using the right glute and left lat to pull into the twist. At the same time this could load opposing musculature, making it easier to power the throw.
The Transverse Abdominus wraps around the belly with horizontal fibers like a belt.
The upper bands fills the gap between the bottom of the ribcage and the top of the pelvis and attaches to the transverse processes of the lumbar spine via the Middle Layer of the thoracolumbar Fascia (MLF).
The lower span of the Transverse Abdominus attaches to the ASISs and inguinal ligament.
ASISs stands for Anterior Superior Iliac Spine. (I also sometimes use ASICs where the C stands for Crest as opposed to Spine). PSIS stands for Posterior Superior Iliac Spine. These pelvic landmarks mark the front and rear points of the crest of the pelvis respectively.
The inguinal ligament joins the ASISs to the pubic bone and creates the crease between lower belly and the top of the thigh.
The Spinal Erectors (or Erector Spinae) and Transverso Spinalis run up the back of the spine from sacrum to skull. Together these muscles can be referred to as the Paraspinalis. In the lumbar region the paraspinalis are made up of the Multifidus, Longissimus and Iliocostalis. The Aponeurosis of the Erector Spinae is common to all of them.
Aponeurosis is connective tissue similiar to tendon that connects a muscle to bone. It differs from fascia in that it has a consistent fiber direction for directing tension.
At the level of the sacrum the aponeurosis of the Spinal Erectors fuses to the overlaying deep and superficial laminas of the PLF.
PLF stands for Posterior Layer of the thoracolumbar Fascia. It actually consists of two lamina (another word for layer in my mind). The superficial lamina is the more rearward and closer to the surface lamina while the deep lamina is more forwards and closer to the center of the body.
In newer texts the deep lamina of the PLF in combination with the MLF tends to be called the Paraspinalis Rectinacular Sheath (PRS). Previous authors viewed the MLF and PLF as separate sheets of fascia that connected at the Lateral Raphe but newer models view the MLF and PLF as a single sheet of fascia which together with its connections to the spine create a tube for the paraspinalis muscles, the Paraspinalis Rectinacular Sheath.
The fused mass of connective tissue that results from the aponeurosis of the Spinal Erectors fusing to the PRS and to the superficial layer of the PLF is called the TLC or Thoracolumbar Composite. It connects the PSIS on both sides to each other as well as to the rear of the sacrum. It in turn connects to the Sacro-Tuberous Ligaments (STL) and via it to the long head of the Biceps Femoris.
The Gluteus Maximus (GM) attaches to rear surface of the TLC as well as to the sacrotuberous ligament. As such, tension in the TLC can serve as a foundation for the Gluteus Maximus. Or, tension from the Gluteus Maximus, contracting from the femur, can add tension to the TLC.
Fibers of the gluteus maximus combine with lower fibers from the contralateral (opposite side) latissimus dorsai. Both of these muscles can be thought of as belonging to the superficial lamina of the PLF.
The Quadratus Lumborum is a muscle located at the back of the body between the bottom of the ribcage and the top of the pelvis. From the crest of the ilium it connects to the transverse processes of the lumbar spine and to the bottom most ribs (rib number 12.)
At the lateral edge of the PRS, there is a seam of connective tissue called the Lateral Raphe which is where the Transverse Abdominus and Latissimus Dorsai makes contact. The fibers of the Transverse Abdominus then blend with the front wall of the PRS where it passes between the Paraspinalis and Quadratus Lumborum. The front wall, thicker because of the intermix of Transverse Abdominus fibers is sometimes referred to as the Middle Layer of the thoracolumbar Fascia or MLF.