The multifidi are deep to (they live underneath) your erector spinae. Those are your strong cords, the big mamas running parallel to the spine that cause the gullies (laminal grooves) that lie directly next to your vertebra (spine bones). You can get up close and personal with your multifidi by sticking your fingers in those long laminal grooves. You can also poke at the multifidi that cover your sacrum (where your spine and pelvis intersect).
So the multifidi run from your sacrum to the third vertebra of your neck (about two clicks under your skull). They’re essentially lacing the different surfaces of your vertebral arches (the bony projections that sprout off your vertebral discs) to one another. Each multifidus inserts into (ends at) the spinous process living two to four vertebrae higher than its origin (or start). Think of it like a corset.
The corset analogy is apt, because the multifidi are essential in maintaining the posture of the spine. Our superficial multifidi keep the spine erect, while our deep multifidi are about stability. I learned from a mcr.coreconcepts.com article that the two sets of multifidi are activated BEFORE any action that involves the core. For instance, if you’re about to pick up something, the mulitifidi start to contract before you actually move to prepare the spine for the movement and to keep it safe.
So what are the multifidi like? They’re fleshy and tendinous bundles of skeletal muscle fibers wrapped in connective tissue, known as fascicles. Ann Archer in her About.com article describes the multifidi as short stiff muscle fibers packed inside a long finger-like covering, and cites recent research that shows this particular construction is responsible for the extra strength and support the multifidus gives to the spine. According to Andrew Biel’s Trail Guide To The Body, the fibers of these muscles “form an intricate stitchlike design that links the vertebrae together,” and he contrasts their short, diagonal fibers to the long, vertical fibers of the erector spinae. When the multifidi contract on one side of the spine, they rotate the vertebral column to the opposite side.
(Actually, if you want to know, they resist the spinal flexion (or bend) that would be caused by the contraction of the abdominal muscles that really power the twist. Individually, your multifidi are more about the stability of your spine than the moving of it. That’s from a Medscape.com article I found!)
Finally, when the multifidi on both sides of the spine fire, they extend the spine (Beil, page 206).
Jim Johnson, a physical therapist and author of THE MULTIFIDUS BACK PAIN SOLUTION, notes that “Your multifidi are active and working when you are: standing still, bending forward, twisting to either side, picking or lifting things up, and walking.” They’re also active if you side bend the spine while leaning it forward or back (i.e., if you’re flexing it to either side without being completely upright). And finally, the multifidi are active if the spine backbends against resistance (Johnson, page 8).
That pretty much covers every single thing you’re going to do today. As a deep stabilizer muscles, your multifidi are turned on most of your day.
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Image: http://www.stephanie-spencer.com (Stephanie Spencer)