How to Draw Lower Back Muscles – Anatomy and Motion
In this lesson we’ll learn about two very important muscles of the lower back – the erector spinae and latissimus dorsi.
Erector Spinae
It originates from the pelvis; more specifically, from the crest of the sacrum and the posterior third of the iliac crest. As it travels up the spine, more fibers originate off the lumbar vertebrae and two lowest thoracic vertebrae to join the group. The erector spinae inserts on all 12 ribs as it passes by, until its final insertion on the mastoid process of the skull. Essentially, the erector spinae is a spine-long arrow and its arrowhead is tucked right into your buttcrack.
The form of the erector spinae is actually split into medial and lateral masses. But, we’ll do a thorough study of the forms in the next lesson.

So using that information, can you guess what the erector spinae’s antagonist is?
That’s right, the rectus abdominis. The erector spinae extends the spine, while the rectus abdominis flexes the spine.

Latissimus Dorsi
Like the erector spinae, the latissimus dorsi originates from the sacrum, the posterior third of the iliac crest, and the lower vertebrae. However, the latissimus is larger than the erector spinae, so it has origin points all the way up through the lower six thoracic vertebrae as well as these points on the lowest 3 ribs. Now, all of these origins are of the lat’s aponeurosis, or tendon.

The actual muscle fibers start farther away from the spine. On a very lean or muscular type, you’ll see the connection of the muscle to the tendon along this curve. On an average person, the lat is pretty thin in the back, so the transition is smooth.
From all these origin points, the latissimus converges toward the armpits and eventually inserts in the bicipital groove of the humerus. More specifically, it inserts between and a little above the inserts of the pectoralis major and teres major.
It actually twists around before it inserts. This means that it overlaps on top of the teres major posteriorly, and then twists around and overlaps on top of the teres major anteriorly as well. The latissimus essentially acts as a sling for the teres major.
Note the overlap at the upper border. The tail of the trapezius sits on top of the latissimus near the spine.
Okay, almost done. We still have to learn the lat’s function. Even though it’s anchored on the lower back, the latissimus inserts onto the arm and the arm is what it moves. Its primary action is to lower the arm. But like, in a cool way. It also helps to extend the arm and rotate it medially. Swimmers use this muscle when they pull down and back against the water. Rock climbers use it when they pull themselves up.

Alright, now you know the anatomical details. In the next video we’ll study the forms of the erector spinae and latissimus dorsi, which will help you draw them.
always great work Stan. thank you thank you
Thanks Leo and you’re welcome
Stan, Very helpful and delightfully informative. Enjoy your outtakes as well.
Thanks Sara! I have a lot of fun making these lessons.
Stan you should upload bloopers to youtube too dude, sometimes i see your bloopers end of the video and they are hilarious. Thanks for the lesson btw you are amazing!
Haha that’s not a bad idea. I might do a compilation of bloopers someday. Glad you enjoyed the lesson!