5 Body Parts You Didn't Know You Had

Sit Bones, Sacrum, Psoas, Piriformis, and Intercostals

Do you know your piriformis from your psoas from your sit bones (sitz bones)? Yoga introduces you to body parts you never knew you had. And once you know about them, you can stretch them out as well as use them to help improve your balance and alignment.

Woman stretching

Getty Images / Nitat Termmee


The Sit Bones (Sitz Bones)

The pelvis

Stocktrek Images / Getty Images

You may hear them called sits bones, sitz bones, or sitting bones. Anatomically part of your pelvis (the ischial tuberosity, to be exact), the sit bones or sitz bones are quite literally the bones under the flesh of the butt that you sit on.

When you sit up straight, you're balancing on your sit bones. You might not realize it, because that area is a little fleshy thanks to the gluteus muscles. Yet, if you gently rock back and forth while seated, you'll notice a difference and can feel the sit bones.

The Yoga Connection

The sit bones affect your posture in seated positions such as cobbler's pose and seated forward bend. Balancing on the sit bones helps elongate your spine and distribute your weight equally on both sides of the body.

To do this, sit up straight and try to feel the sit bones on either side of your pelvis pressing into your mat. You may even push the flesh of your butt to the side and out of the way.


The Sacrum

Sacrum, illustration

The sacrum is the triangular bone at the base of your spine, right above your tailbone. It is a common source of lower back pain and home to a number of nerves. It connects to the hip bones via the sacroiliac joint (SI joint). This SI joint can become misaligned and is a common source of pain. Ask your yoga teacher about ways to mitigate and prevent this, particularly if you've injured it before.

The Yoga Connection

The muscles surrounding the sacrum can be stretched and twisted in a number of yoga poses, and it's easy to take them too far. In poses in which you are lying on your back, the sacrum should usually stay down. Your teacher will likely remind you of this often, telling you to "protect your sacrum" and to move slowly and deliberately.


The Psoas

The Psoas Major Muscle
SCIEPRO / Getty Images

The psoas major is one of the groups of muscles that are called hip flexors. These work together to bring your leg and torso toward one another into a position of flexion (like a crunch).

The psoas (pronounced "so-az") inserts in the upper interior of your femur (thigh bone) at one end. It then passes through the pelvis and connects to several of the lower vertebrae as it fans out at the other end.

Since the psoas is not a surface muscle, it can be difficult to identify and isolate. Its anonymity does not decrease its importance, though. The psoas is key to the cultivation of core strength and hip flexibility. Strengthening and lengthening the psoas is key for anyone suffering from back pain due to sitting too much.

The Yoga Connection

The psoas is particularly important in balancing as well as bending forward and backward. Poses for the psoas include tree pose, standing big toe pose, king dancer pose, and warrior I pose.


The Piriformis

The Piriformis Muscle

Behind the psoas is a muscle called the piriformis. It's possible for this muscle to become either too tight or too loose and cause all sorts of pain. Stretching this little muscle in your butt can have a big impact if you're dealing with sciatica.

The Yoga Connection

The piriformis is a key muscle in leg rotation, allowing you to turn it outward from the hip. It is also a key to the support system for the sacrum. When your teacher offers suggestions to improve pelvic alignment, the piriformis is often the target.


The Intercostals

External intercostal muscles
MedicalRF.com / Getty Images

If you have ever felt sore around your ribs after a lot of back bending or twisting, your intercostals are talking. These muscles are responsible for the expansion and contraction of your rib cage when you breathe. They not only allow the lungs to expand and contract, they also affect your posture.

The Yoga Connection

The rib cage plays a big role in your practice. Poses such as cow face pose and gate pose can do wonders for stretching and opening up the intercostals. It's easy to neglect these, but the chest muscles are just as important in yoga as any other muscles.

5 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Gothe NP, Mcauley E. Yoga Is as Good as Stretching-Strengthening Exercises in Improving Functional Fitness Outcomes: Results From a Randomized Controlled Trial. J Gerontol A Biol Sci Med Sci. 2016;71(3):406-11. doi:10.1093/gerona/glv127

  2. Vleeming A, Schuenke MD, Masi AT, Carreiro JE, Danneels L, Willard FH. The sacroiliac joint: an overview of its anatomy, function and potential clinical implications. J Anat. 2012;221(6):537-67. doi:10.1111/j.1469-7580.2012.01564.x

  3. Otsudo T, Mimura K, Akasaka K. Immediate effect of application of the pressure technique to the psoas major on lumbar lordosis. J Phys Ther Sci. 2018;30(10):1323-1328. doi:10.1589/jpts.30.1323

  4. Ro TH, Edmonds L. Diagnosis and Management of Piriformis Syndrome: A Rare Anatomic Variant Analyzed by Magnetic Resonance Imaging. J Clin Imaging Sci. 2018;8:6. doi:10.4103/jcis.JCIS_58_17

  5. Hudson AL, Butler JE, Gandevia SC, De troyer A. Interplay between the inspiratory and postural functions of the human parasternal intercostal muscles. J Neurophysiol. 2010;103(3):1622-9. doi:10.1152/jn.00887.2009

By Ann Pizer, RYT
Ann Pizer is a writer and registered yoga instructor who teaches vinyasa/flow and prenatal yoga classes.