The multifidi are deep muscles running along either side of the spine from C4 through L5, with the lowest attaching to the tailbone (sacrum). They are responsible for extension of the vertebral column and rotation to the opposite side. The lumbar multifidus is responsible for stabilizing the low back during movement. When things are working properly, the multifidi and other core stabilizers contract automatically prior to beginning movement. When this doesn't happen, the spine is not stabilized, and back pain may develop. In this case, the contraction of the lumbar multifidus may need to be re-learned and practiced.
Lie on your back with your knees bent and feet planted.
Think of tilting your tailbone (sacrum) forward as if you are going to arch your back -- but don't actually move. This is an isometric contraction, meaning no movement should actually occur.
Allow the lumbar multifidus to swell on either side of the vertebrae.
Hold the contraction and continue to breath normally. Aim for a 10 to 15 second hold.
Check yourself. Use two fingers and find your lumbar spine. Slide your fingers just to the side of the spine. You should feel a slight inflation or contraction of the lumbar multifidus. If the contraction is very strong or you are feeling additional movements, such as an arching back, you are probably activating the wrong muscle.