the multifidus
Below is a short version of a handout.
Bottom line is that most people (including myself) must do stabilization exercises to strengthen their inner unit.
Back pain is complex, to say the least, but heres a common scenario........
The multifidi from the sacrum up to lumbar 3 are often involved with muscle-based back pain.
The Multifidi to the L3 transverse process irritates QL, and that activates the iliocostalis.
Glut medius- especially the posterior part that attaches to the PSIS- and glut minimus are almost always involved with chronic LBP
THE HANDOUT
The INNER UNIT became accepted as a term describing the functional synergy between the
1) Multifidus
2) Transversus Abdominis
3) Pelvic floor muscles
4) Thoracolumbar fascia
5) Lumbar portions of erector spinae
6) Posterior fibers of the internal oblique
When working properly, these muscles provide the necessary increases in joint stiffness and stability to the spine, pelvis and rib cage to provide a stable platform for the big muscles.
The inner unit is under separate neurological control from the other muscles of the core. This explained why exercises targeting muscles such as the rectus abdominis, external obliques, and psoas, (the same muscles exercised in traditional abdominal conditioning programs common allover the world) were very ineffective at stabilizing the spine and reducing chronic back pain.
Exercising the big muscles (prime movers) was not providing the correct strengthening for such essential small muscles as the multifidus, transversus abdominis and pelvic floor muscles.
In a sense, as the big muscles (outer unit) become stronger and tighter, the delicate balance between the inner and outer units becomes disrupted.
This concept is easier to understand using the pirate ship model. (picture missing)
Although the large guy wires (outer unit) support the mast of the pirate ship, its functionality is completely dependant upon the support provided by the small guy wires which represent the multifidus and inner unit muscles in this analogy.
The mast of the pirate ship is made of vertebra, which is held together (stabilized) by the small guy wires running from vertebra to vertebra, just like the role of the multifidus (a member of the inner unit) in the human spinal column.
Although the big guy wires (representing the outer unit) are essential to hold up the mast of the pirate ship (our spine), they could never perform this function effectively if the small segmental stabilizers (inner unit) were to fail. By viewing the pirate ship's large guy wires, it becomes easy to see how developing too much tension from the overuse of exercises such as the crunch, could disrupt the posture of the mast, or spinal column in the case of a human.
Bottom Line: most back involve problems with the MULTIFIDUS
While the multifidus is really a group of muscles, it's referred to in the back literature in the singular. However, it is not just one big muscle that runs all the way from the top to the bottom. Instead, it takes many individual multifidus muscles combined, each crossing two to five levels of vertebrae, and often several layers thick โ especially the lumbar multifidi. In this way, the multifidus is capable of gaining fine control over just a single segment of the spine.
Researchers are now finding out that in some people with low-back pain, it's not always the whole multifidus muscle group that is the problem. In many cases, it's just a single multifidus muscle at only one level of the spine that's not working properly.
Multifidus is different from all the other back muscles in that each multifidus muscle gets its nerve messages from only one level of the spinal cord. Anatomists call this being segmentally innervated. What this means to the multifidus muscle is that it can be more prone to having problems. Other back muscles have nerves coming from several different levels of the spine to power them, so that if one nerve doesn't work well, it still has the others to help it out.
Another interesting anatomic fact about the multifidus is that it's connected to each of the small joints in your spine, also known as the facet joints. It does this by way of its attachment directly to the joint capsule. This is significant for the spine's function, as the multifidus can exert a pull on this capsule and prevent it from becoming caught inside the joint as you move your back throughout the day.
The multifidus is the only muscle on the posterior sacrum, thus - the only muscle directly stabilizing the lumbosacral joint. The lumbar erector spinae consist primarily of tendons and cross several joints so they have little to do with lumbar stabilization
Experimental Observations of Those With Back Pain:
ยทMuscle activation -- less activity of Multifidus at unstable level during concentric back activity, suggesting decreased muscular protection at the hypermobile segment.
ยทFatigability -- Patients demonstrated greater fatigability of the Multifidus. This even occurs in elite athletes with history of low back pain (LBP).
ยทSize and consistency -- Many patients may have severe changes in Multifidus after lumbar surgery. In patients with unilateral LBP there is marked side-to-side asymmetry of the size of the MF, with the smaller muscle on the symptomatic side and level. Changes can occur within 24 hours of injury.
ยทRecurrent LBP-- Multifidus recovery is not spontaneous upon pain relief or when patients returned to normal activity levels. Patients with recurrent LBP typically have pathological changes and selected atrophy of type II fibers. Multifidus dysfunction reduces the ability of a facet joint to transmit loads; therefore loads are shifted to the disc and ligaments.
ยทMultifidus Atrophy--wasting may occur without erector spinae atrophy
ยทSurgical Patients. Patients with negative outcome s/p diskectomy may have persistent "selective multifidus fiber atrophy", "pathological inner structure changes",