The Multifidus – maybe the most important muscle you’ve never heard of.

January 30, 2015

When I mention the Multifidus muscle to my patients, I’m often met with quite a puzzled look. If you asked your average person on the street to name 10 muscles in the body, it’s safe to say that the Multifidus would be notable by its absence; very few have heard of it. Don’t be fooled by its anonymity, however, this lesser-known muscle plays a vital role in back stability and, therefore, in back pain and here’s why…

Firstly, where is it?

The Multifidus is made up of many small, segmental muscles that run the entire length of your spine from your pelvis to the highest vertebra of your neck. It is a deep back muscle that, for the most part, is covered by larger muscles making it difficult to feel (or ‘palpate’). The best place to palpate the Multifidus is at the base of the lumbar spine, where it is only covered by a thin layer of fascia. If you locate the central bony aspects of at the base of your spine (called the spinous processes) and then drop off into the soft tissue either side, you will be sitting over the Multifidus.

What does it do?

The Multifidus muscle is highly active in almost all daily movements. The nature of the muscle attachments, some fibres travelling from one verterbra to another and others attaching groups of 2 or 3 vertebrae, mean that it is involved in gross movements as well as small segmental movements in the spine. In short, this means that the muscle fibres can group together to allow the spinal column to extend or side bend, for example, but can also control fine movements at an individual spinal level. The Multifidus is, therefore, a crucial back stabiliser and offers up to two thirds of the total muscular stability afforded to the back.

Why is it so important?

Each muscle must receive input from the nervous system in order to become active. For most large muscle groups, these innervations are received from nerves exiting the spinal column at a group of spinal levels. For example, the quads receive their power via the femoral nerve exiting the spine at L2, 3 and 4. The Multifidus at each level of the spine, however, receives its neural innervations from nerves exiting at only that level. To explain more clearly, your Multifidus at L1 is being innervated by the L1 nerve root. This means that there isn’t much of a backup plan if that spinal level is for any reason compromised. Research shows that the Multifidus can weaken and become smaller at an individual level if, for example, there is vertebral instability at that level.

What causes back pain?

There are many apparent causes of back pain, from disc injury to joint approximation or degeneration for example, but interestingly such presentations are far from black and white. Studies on pain-free people have shown that many of the things that you would expect to cause back pain are in fact present in those without pain. Jensen et al (1994) found that 64% of people reporting NO back pain showed abnormal discs on MRI. Hitselberger et al (back in 1968) found that 24% of those studied with NO back pain showed nerve compression using a Myelogram. I’m not arguing that disc injury and nerve compression do not cause pain, but it would seem that there are many people with apparent ‘abnormalities’ who are in fact asymptomatic.
This brings us onto the Multifidus. Is Multifidus weakness another abnormality that can either be painful or cause no pain? Well, it would seem not. Studies by Spine (1995) and Stein (1993), among others, have shown very few Multifidus abnormalities in asymptomatic patients. One could argue, therefore, that there are very few pain free people walking around with abnormal Multifidus muscles.

So when do Multifidus abnormalities happen?

Ultrasound techniques have show the Multifidus to be smaller on one-side of the back in patients with acute and sub-acute back pain, notably on the same side of the patients pain. Wasting has been found to occur mainly at a single vertebral level. In chronic patients, the Multifidus has been shown to be smaller over a number of vertebral levels when comparing patients to healthy control subjects. MRI tests also reveal a correlation between Mutlifidus wasting and leg pain in chronic pain patients. Multifidus changes have also been seen in cases of disc herniation, vertebral instability, post surgery and in those with back pain in pregnancy.

Strengthening your Multifidus as a solution to back pain…

It has been shown that Multifidus exercises can increase the size and symmetry of the muscles and lead to improved recovery from back pain, as well as less frequent and less significant back pain episodes in the future. As with any muscle building and strengthening, improving Multifidus muscle tone takes commitment. It is advisable to exercise the muscle at least 3 times a week and you may have to wait 4-6 weeks before you start seeing any improved stability in the spine. I have put an illustration of my favourite Multifidus exercise on a link here. This is a very functional exercise and mimics the activity of the Multifidus in your walking cycle. The benefit of this exercise is that you will begin to retrain the neurological input to the muscle so that it activates properly during walking, thereby, increasing its activity during your daily pursuits. For floor based exercise, have a look at the video on this link.