The Erector Spinae Group (ESGs) consist of three sets of muscles that run along both sides your spine and support the spine from the sacrum all the way up to base of your head. The muscle that is the closest to the spine is the Spinalis, which is also the smallest of the three muscles. The next one is Longissimus and is the longest in the group. The third muscle in the group is the Iliocostalis and extends over the ribs.
All three of the ESGs work together to keep your spine erect. The functions and movements of this muscle group are the same for all three. Bilaterally (since the muscles run on either side of the spine) they contract to stabilize the spine to allow you to be upright, as well as pull you even further back as if you are getting ready to do the limbo. When lengthened bilaterally, you are able to fold over forward to reach for your toes. When only one side of the muscles are contracting, it causes you to unilaterally bend to that same side, bending your torso in lateral flexion.
Your Erector Spinae Group are a very important group of muscles that work together to support your torso and spine in everyday activities. Bending forward, backward, to either side, and even rotating and twisting your torso can become painful and difficult if these muscles are not feeling their best. Take care to strengthen, stretch, and even massage these muscles on a regular basis. Your body and balance will thank you.