Demystifying 10 Anatomical Terms You've Probably Heard in Yoga

In the early years of my teaching career, my understanding of human anatomy and biomechanics was virtually nonexistent. I chose many of the words I used to instruct because they were what my teachers used, like a game of telephone. Over the years, as my investigation of anatomy and related sciences has deepened, I have been forced to examine the language I have heard, and therefore used, and compare it with the long-established technical language related to the body. 

As a trainer of yoga teachers, I now teach anatomy and movement science. My students are often confused as they seek to compare previously held notions with new information. While I do not find it necessary, or even always helpful, to use anatomical language in our classes, to the extent that we choose to, I do believe it’s important that we yoga teachers do so with accuracy. 

A student of yoga will be required, in addition to learning new motor skills, to learn new words, pose names, Sanskrit terms, and the language of anatomy and human movement. Whether you are a teacher or a student, you have probably used, or heard, the following terms in a yoga class, and they might benefit from some demystification and clarity:

1. Flexion/Extension

You have probably been cued to “Flex your biceps” or other muscle group, or to “Extend through your fingertips” as a means to engage your muscles or lengthen through your limbs. While the instruction to flex a muscle or extend through a limb may produce the desired effect, it is a misuse of the anatomical terms. 

Flexion and extension describe joint positions. You may have heard the cue to extend your arms overhead, which does not reflect the anatomical action at the joint. When you move your arms forward and up overhead, your shoulder (or glenohumeral) joint flexes. When you bend your elbows, your elbow joint flexes. Likewise, moving your arms behind you and straightening your elbows are both forms of extension.

It would be accurate to say that flexing your elbows requires a concentric contraction of your biceps (they shorten) and an eccentric contraction of your triceps (they lengthen), and can result in either muscle group’s engagement. Conversely, straightening your elbows extends the joint and produces an inverse effect on the muscle contractions. Flexion and extension can also occur in your spine, hips, knees, wrists, fingers, and toes.

2. Sit/Sitting/Sitz Bones

All three of these terms are common ways of referring to the ischial tuberosities, a pair of bony protrusions on the bottom of your pelvis that serve as attachment sites for various muscles and are your base of support when sitting. It is a common reference point in seated poses, for which you may have been instructed to “Root down through your sit bones.” It would be accurate to say that you have two sit, or sitting bones, which you use to sit (sitz comes from the German verb sitzen, meaning “to sit”). All terms are acceptable alternatives to “ischial tuberosities.”

3. Compression

Compression refers to a type of mechanical force that occurs when a physical force presses on an object or body part. That force is then distributed throughout our body, which has many structures between our joints to help cushion it (i.e., intervertebral discs), as well as adaptations that have rendered the bones that receive more force thicker and denser as we develop and evolve over time.

For example, as we move from supine to crawling, to sitting, to standing throughout our early stages of development, our spines receive progressively more compressive force, and therefore the bodies of our lumbar vertebrae become significantly larger and more dense than those of our thoracic and cervical spine, which receive much less compression when we are upright.

I often hear compression used negatively in classes to imply that it will lead to damage. For example, in bridge pose I was often told to keep my feet parallel and my hips neutral in their rotation to avoid compressing, or damaging my sacrum. 

Thick bones like our sacrum can withstand relatively high levels of compression. In fact, as you read this, your sacrum is probably being compressed by your spine, which is being compressed by your skull. 

While it can, for example, be nice to suspend, hang, and “decompress” the spine, compression is not to be feared, unless it is being done at levels beyond what you can tolerate. Placing a 100-pound weight plate on your head may result in excessive compression, but if you have been building the intrinsic strength to support this degree of compression, it could be manageable. As always, it really depends. 

4. Psoas/Hip Flexors

I often hear these two terms used interchangeably. Let’s examine each. Your hip flexors are a group of muscles that shorten to produce flexion at the hip joint. The psoas is only one hip flexor. The rest include the iliacus, rectus femoris, sartorius, and tensor fascia latae. Different angles of hip flexion will engage different muscles.

The psoas connects your lower spine to your top inner femur. Its primary action is hip flexion. In poses like warrior I (front leg), chair pose, and boat pose, your psoas is shortened. In poses in which your legs are extended (back leg of crescent lunge, up dog, upward bow pose, etc.), the psoas is lengthened. Because we tend to spend a lot of time sitting, our psoas can get stuck in a shortened position and become weak. Therefore, the strengthening and lengthening of the psoas can be useful in increasing our mobility and posture. 

5. Contract vs. Engage

Have you heard the instruction to “Contract your quadriceps” or “Engage your core”? “Contract” and “engage” are two other terms that are often used interchangeably, though they are not actually the same. Technically, a muscle contraction occurs when the muscle fibers change length. They can shorten (concentric contraction), lengthen (eccentric contraction), or stay the same length (isometric contraction). This does not, however, refer to the activation of the muscle, or its level of engagement. 

For example, when I flex my elbow, my bicep contracts concentrically and my tricep contracts eccentrically. Depending on the position of my arm in space and the resistance present, the muscles that are more passive or active (engaged) will change. 

6. Protraction and Retraction of the Scapula 

Protraction and retraction refer to two of the six possible movements of your shoulder blades, or scapulae. Your shoulder blades moving toward your spine is called scapular retraction; when they move away from your spine it is referred to as scapular protraction. Often the cue to “Move your shoulders back” or “Plug your arm bones into the sockets” is instructing scapular retraction. In quadruped poses or arm balances in which we are told to “Push the floor away,” this results in scapular protraction. Retraction and protraction are both useful movements to strengthen and mobilize. Elsewhere in the body, protraction and retraction occur relative to the skull’s position atop the spine. 

7. ASIS Bones

If you palpate (touch) the front of your pelvis you will feel two bony protrusions on either side just below your waist and above your hips. These bones are often referred to as your “frontal hip bones” or “hip points.” I find this labeling a bit confusing, as they are more a part of your pelvis than your hip joint. They are referred to anatomically as the anterior superior iliac spine (ASIS) bones, as they are on the front (anterior), upper (superior) portion of the ilium’s spine.

While they are attachment sites for the sartorius muscles, they are often used in a yoga class as a reference point for assessing the position of your pelvis (i.e., “Turn your pelvis so your ASIS bones point straight forward” or “Lift your frontal hip bones toward your bottom ribs”).

8. Pelvis vs. Hip Joint

These terms are, again, often used interchangeably for understandable reasons. Your pelvis is the large bony structure at the base of your trunk. It is often referred to as a basin, and its movements likened to that of a bowl being tipped in various directions. Your spine connects to your pelvis via your sacrum, and your legs attach to your pelvis in the two sockets called acetabulum on either side of your pelvis. 

Your hip joint refers to this ball and socket connection between your femur and pelvis. While movement of the pelvis almost always results in movement at your hip joint, it is possible to articulate your hip joints without changing the position of your pelvis. As you become more interested in refining your movement skills, discerning between movements at your hip joint and movements at the pelvis can be useful.

9. Anterior and Posterior

These are directional terms that refer to the relationship of various body parts to each other. Anterior describes the front or direction toward the front of the body, while posterior describes the back or direction toward the back of the body. For example, your shoulder blades are posterior to your sternum, and your pubic bones are anterior to your sacrum. 

As movement terms, anterior and posterior are used most notably to describe two of the possible movements of your pelvis. If you imagine your pelvis as a bowl of water, an anterior tilt would spill the water forward, and a posterior tilt would spill the water back. An anterior pelvic tilt often produces hip flexion, while a posterior pelvic tilt produces hip extension. A posterior or anterior tilt may be necessary to bring your pelvis back to a neutral position, but in anatomical neutral the basin of the pelvis is supporting this imaginary water without spilling in either direction. 

10. Lordotic and Kyphotic

These terms refer to the natural curvature of your spine. We all have different degrees of curvature along the various regions of our spine, but the concave, inward curve (in our lumbar and cervical spine) is referred to as lordotic, and the convex, outward curve (in our thoracic spine) is called kyphotic. These curves form as a part of our embryological and infant developmental movements and ultimately support us in standing upright on two legs. 

When we flex our spine we increase the kyphotic curve and decrease the lordotic curve, and vice versa when we extend our spine. You may sometimes hear these curves referred to as “lordosis” or “kyphosis” when they appear to be exaggerated.  While there is no general consensus on this labeling, the “osis” will typically refer to an excess of curvature in either direction beyond the normal range. Similarly, scoliosis refers to excessive lateral curvature in the spine. 

Context and Clarity

It’s worth noting again that yoga and movement can be taught and experienced in incredibly meaningful ways without the use of technical anatomical language. In many instances, communicating instructions with the use of these terms can lead to more confusion than clarity when they are not properly defined, explained, and used. 

I hope I have provided enough clarity so that you know whether you are using these terms incorrectly/inconsistently or, if you have heard them used without much explanation, that you understand them. Further, as the yoga world continues to merge its history and traditions more and more with other interdisciplinary forms of movement and knowledge, I hope that this shared language can build bridges of communication and connection between vast and diverse practices.

Photography: Andrea Killam