A growing amount of research indicates that the lumbar multifidus muscle may be the key to many instances of chronic lower back pain.
The multifidus muscle stretches from the sacrum to the bottom of the skull and runs along the spine. Its thickest part is located in the lower back. Though relatively thin, this muscle is largely responsible for the alignment and stability of the spine; some estimate it is responsible for 2/3rds of spinal stability. Its superficial layer supports alignment, while the deeper layer is responsible for stabilization. By supporting the spine, the muscle takes undue pressure off spinal discs.
The multifidus mainly comes into play when bending backward, bending sideways and turning to one side. The muscle can become strained during these actions if the position is held for too long, if you are carrying an object or if the muscle is weak. Sports are a common reason for multifidus injury.
After any muscle is injured, it needs to be rested for a day or two to recover. What researchers are now considering is the possibility that the multifidus atrophies quickly after injury, meaning that those who do not take steps to rebuild the muscle post-injury are susceptible to recurrent back pain. The quick atrophy may be caused by the fact that the body readjusts posture and movement patterns to avoid pain.
A 2009 study by MacDonald et al sought to answer why 34% of people who experience lower back pain experience recurrence. They compared the multifidus muscle activity of healthy patients with those who have recurrent pain. The muscle normally activates before it is needed in order to prepare the spine. In the group with lower back pain, the muscle engaged later than in the healthy group. This lack of spinal support when needed increases the risk of further injury and pain.
The study can be found at http://www.ncbi.nlm.nih.gov/pubmed/19186001.
Rebuilding the Multifidus
The loss of muscle size and strength due to atrophy combined with delayed activation may be responsible for chronic lower back pain in many individuals. Any type of back pain or injury can lead to disuse of the multifidus, so strengthening this and other core muscles is a sound component of any back pain recovery plan.
The back bridge exercise engages the multifidus most. This exercise also engages the deep abdominal and gluteal muscles. The best way to prevent multifidus strain in the future, along with practicing proper body mechanics, is to develop the core muscle group as a whole; this will provide support to the muscle and ensure it is not compensating for other, weaker ones. See the Mayo Clinic’s slideshow of core workouts at http://www.mayoclinic.com/health/core-strength/SM00047. If your back pain is severe, you should consult a physical therapist to guide you through exercises that do not exacerbate your pain.
If you suffer chronic lower back pain, then your body has adapted to that pain by changing its movement patterns. In this case, less short-term pain means more long-term pain. A weak multifidus muscle leaves your spine susceptible to injury. Conditioning this and other core muscles could be the answer to your pain.