The erectors are a powerful group of muscles on the back that start on the sacrum and climb the spine and ribs all the way up to the occiput. Like a lot of muscles, the ESG has the potential to get complicated/confusing really quickly, but I’m here to break it down in a way that hopefully makes a lot of sense to you.
Firstly, we’re looking at three muscles here: spinalis, longissumus and iliocostalis. Spinalis is closest to the spine, or the most medial of the three. It climbs the spinous processes. Just lateral to the spinalis is the longissumus, the middle of the three erectors. It climbs the transverse processes. The most lateral of the three is the iliocostalis. If you really think about the name of that muscle it will tell you exactly where it is- on the ilium and the ribs (costal means rib). The iliocostalis climbs the ribs.
Let’s talk about the commonalities.
Spinalis, longissimus and iliocostalis all work together to produce the same movements. When the fibers on the right contract, the spine laterally flexes to the right. When the fibers on the left contract, the spine laterally flexes to the left. Lateral flexion is a side bend. When all of the fibers work together and contract at the same time, the spine extends. The upper fibers of these three muscles also assist in laterally flexing and rotating the head and neck to the same side, as well as extending the head and neck.
In addition to sharing the same actions, they also share a point of origin on the thoracolumbar aponeurosis, also known as the common tendon. The thoracolumbar aponeurosis is a broad, thick, diamond-shaped tendon that goes from the sacrum over to the ilium and then up the spinous processes of the lumbar vertebrae to the lower thoracic vertebrae.
Let’s look at them individually, starting with the medial spinalis. The spinalis muscle originates on the common tendon (spinous processes of the upper lumbar and lower thoracic vertebrae) and the ligamentum nuchae as well as on the spinous process of C-7. The ligamentum nuchae is the big, thick neck ligament.
Doesn’t that seem weird that it starts in one spot, skips over a spot in the middle and then starts again somewhere higher up?
This works because the muscle inserts on the spaces in between. In this case the insertion is on the spinous processes of the upper thoracic vertebrae (this is between the two points of origin) and then also on all of the spinous processes of all of the cervical vertebrae (except for C-7, because the muscle originates there). To me, it feels less important that you remember exactly where the origin/insertion is and more important that you remember the muscle climbs the spinous processes and pulls the spine backward into extension.
The middle muscle is called longissimus. It’s the thickest and, hence its name, the longest of the three. It originates on the common tendon as well as the transverse processes of the first five thoracic vertebrae (T-1 through T-5). The spinalis climbs the spinous processes while the longissimus climbs the transverse processes. Like the spinalis, the longissimus also does that thing where it starts, skips some space and then starts again. It inserts itself between the two points of origin on the lower 9 ribs (ribs 4-12), the transverse processes of all of the cervical vertebrae (C-1 through C-7) and the mastoid process of the temporal bone, which is behind the ear. You can easily feel this one on yourself or someone else, it’s about two inches wide and its cable-y fibers are on either side of the spine.
If you don’t remember anything else about the longissimus, remember that its the middle erector as well as the longest, thickest and most easily palpable.
Iliocostalis is the rib climber. It originates on the common tendon and the posterior surfaces of all the ribs (1-12). To get over to the ribs, it inserts on the transverse processes of the first three lumbar vertebrae, then climbs the posterior surfaces of all the ribs to get the the transverse processes of the lower cervical vertebrae.
Bhujangasana (cobra pose) is a great way to strengthen these commonly tight but overstretched muscles. I like to practice and teach this one with strong legs and little to no weight in the hands to really get these muscles firing.