by Doug Keller
The name comes from a combination of the Latin words multus, meaning ‘many’, and findo, meaning ‘to cleave’. The name really refers to a group of many tiny individual muscles that ‘cleave’ the facet joints of the spine, interwoven from the top of the sacrum all the way up the base of the head. There are lots of multifidus muscles, each one crossing just two to five vertebrae each. As a whole, the multifidus muscles work together to provide stability to the spine, keeping the vertebrae in a safe position regardless of what the spine is being asked to do. And each multifidus has an individual job to do, controlling its own single segment of the spine.
And that can be the problem. In many cases of back pain, it’s just a single multifidus muscle – rather than the group – that is not working properly, and there is plenty of evidence linking failure of a single muscle to the specific area of back pain. And each multifidus is particularly vulnerable to a breakdown. Most muscles in the body are controlled by several nerves, which means that they have a backup to keep them running if one nerve fails. But the multifidus is rather unique, in that each of them is run by a single nerve from the spinal cord. If something happens to the nerve, the muscle stops functioning properly, like a single light going out on the Christmas tree. Since it lacks a backup, the multifidus is more prone to failure.
Why would this cause back pain? Because of the specific job entrusted to it. Each multifidus attaches directly to the joint capsule or tissue that surrounds the small facet joints at the back of the spine. When the multifidus contracts, it pulls backwards on this capsule, pulling the capsule or tissue that surrounds the small facet joints at the back of the spine. When the multifidus contracts, it pulls backward s on this capsule, pulling the capsule away from the bones of the joint so that it doesn’t get nipped or pinched by the vertebrae as you bend forward or twist. Since the capsule contains nerve endings, any pinching of the capsule will result in an attack of back pain, even if you’re doing simple everyday movements that never caused pain before.
But back pain from the multifidus does not arise only from pinching of the joint capsule. Often it is the muscle itself that is crying out in pain. Paradoxically, back pain often arises when the multifidus muscles don’t relax and release they’re supposed to! In the case of pregnant women – where the increasing weight of the child steadily increases the load on the spine – studies have found that the increased activity in the multifidus goes hand in hand with the increasing intensity of back pain that comes with pregnancy. In fact, measurements of increased activity in the multifidus provide a good predictor of which pregnant women will suffer from back pain.
In cases of disk herniation, we’re finding that the effect upon the mutifidus is also involved. Though the casual relationship is not fully understood, it’s been found that a herniated disk causes the multifidus to be overactive and contract more than it should. Moreover, the multifidus muscles in the area of the herniation have been shown to be much smaller (hence weaker) than normal. By the same token, studies have shown the exercises for the lower back muscles in cases of disk herniation have had high success rates in overcoming back pain.
An overworked multifidus muscle is weak and stressed, and even smaller or shrunken. A strong muscle, it seems, is also one that is able to relax and release when it ought to.
*Yoga As Therapy, Volume Two: Applications
Multifidus Muscle Atrophy and Association with Low Back Pain
Dysfunction in the lumbar multifidus muscles is strongly associated with low back pain. The dysfunction can be caused by inhibition of pain by the spine. This dysfunction frequently persists even after the pain has disappeared. Such persistence may help explain the high recurrence rates of low back pain. Persistent lumbar multifidus dysfunction is diagnosed by atrophic replacement of the multifidus with fat, as visualized by magnetic resonance imaging or ultrasound. One way to help recruit and strengthen the lumbar multifidus muscles is by tensing the pelvic floor muscles for a few seconds “as if stopping urination midstream”.
More at Wikipedia
Rafael Durán 