The Skeletal System in Yoga: Bones, Shape and What They Allow

Ask a room of students why they cannot get into a posture and almost all of them will answer that they are not flexible enough. Sometimes that is true. Often the real answer is the skeletal system — the shape of the bones they were born with, which no amount of practice will change and which decides the outer limit of every shape they will ever make.

This is the second post in our anatomy series and the place to start, because everything else sits on top of it. Muscles pull on bones. Joints are where bones meet. Movement is what the skeleton permits. If you only learn one system properly, learn this one.

As with everything in this series: this is anatomy for teaching, not for treating. It is here so you can modify honestly and adjust safely. Pain belongs to a doctor.

What the skeleton actually is

The skeletal system is the body's bones together with the cartilage and joints that connect them — the hard framework the whole body is built around. An adult skeleton has 206 bones.

A child has more. As growth proceeds some bones fuse: the ilium, ischium and pubis become the single pelvic bone, five sacral vertebrae become one sacrum, four coccygeal vertebrae become one coccyx, and the two halves of the infant frontal bone and jaw close up. The skeleton you teach to is not the one anybody started with.

Two divisions: axial and appendicular

The skeleton divides into a center and a set of extremities, and the two behave very differently in practice.

The axial skeleton — the center

• Skull. The bony frame of the head, 22 bones in two groups — the cranium and the face.
• Vertebral column. A flexible column of 33 vertebrae connecting the trunk to the skull and the limbs, in five regions: cervical, thoracic, lumbar, sacral and coccygeal.
• Rib cage. Twelve pairs of ribs and the sternum, forming a bony cage around the organs inside it. The ribs come in three groups — true, false and floating.

The appendicular skeleton — the extremities

• Shoulder girdle. Attaches each arm to the trunk, and is only two bones: the clavicle and the scapula.
• Upper limb. Thirty bones each: humerus, ulna, radius, eight carpals, five metacarpals and fourteen phalanges.
• Pelvic girdle. One for each leg, meeting at the symphysis pubis. In an adult each is a single bone made of three fused parts — ilium, ischium and pubis.
• Lower limb. Thirty bones each: femur, tibia, fibula, patella, seven tarsals, five metatarsals and fourteen phalanges.

The shoulder girdle is worth pausing on. The entire arm is attached to the rest of the skeleton by two bones and a great deal of muscle — which is exactly why the shoulder can travel so far and exactly why it is the joint most often overloaded in a weight-bearing practice.

What bones do — four jobs

Strength, support and shape. Without a rigid frame the body could not stand upright at all; it would be a bag of soft tissue with no particular form. Posture is a skeletal question before it is a muscular one.

Protection. The rib cage and the skull are armor around organs where damage is fatal. This is the most direct safety lesson in the whole subject: the neck and the lower back are the two places where the protection thins out, and they are the two places a careless adjustment does the most damage.

Leverage for movement. Bones give muscles something to attach to. When a muscle contracts, the bone acts as a lever. Every posture in every style is levers.

Producing red blood cells. Bones such as the sternum and the heads of the tibia produce blood cells. Bone is living tissue with a blood supply, not scaffolding.

The four types of bone

Bones are classified by shape, and the shape tells you the job.

Long bones have an elongated shaft with an expanded end on either side, and a central medullary cavity holding the marrow. They come in three kinds: typical long bones (humerus, femur, radius, ulna, tibia, fibula), miniature long bones (the metacarpals, metatarsals and phalanges of the hands and feet), and modified long bones such as the clavicle and the bodies of the vertebrae, which have no medullary cavity.

Short bones are short in stature and can be almost any shape; most are named for the shape they have.

Flat bones have two broad surfaces and resemble shallow plates, forming the boundaries of body cavities — the scapula, the ribs, the sternum.

Irregular bones fit no category at all: the vertebrae, the hip bone, the bones at the base of the skull.

Standing on your hands is asking long bones to do a job they do well. Sitting on your heels is asking irregular and short bones in the foot to tolerate a load. Knowing which is which is how you predict where a student will feel a shape before they tell you.

Why the skeleton is the honest answer to “why can’t I do this pose”

This is the part a teacher uses every single day.

A training course teaches general anatomy — the shared pattern. But no two bodies are anatomically identical. They may be similar; they are not copies of one another. Hip sockets differ in depth and in the angle they face. Femur necks differ in length and in how far they are turned. Spines have different natural curves.

Which leads to the sentence worth repeating to a class: no two practitioners will perform the same posture in exactly the same way. A shape that looks correct on one skeleton is wrong on the next, and the student whose hips stop earlier is not less dedicated. They have different bones.

Soft tissue responds to practice. Bone shape does not. When a student meets a hard stop that feels like bone rather than stretch, the correct teaching response is to change the shape, not to encourage more effort into it. That distinction between a limit you can work with and a limit you must respect is covered in detail in compression and tension in yoga.

What this changes about how you teach

• Cue toward a sensation and a direction, not toward a photograph. “Lengthen through the spine” works on any skeleton; “get your forehead to your knee” does not.
• Offer the modification before the posture, so nobody has to fail publicly first to be allowed to take it.
• Treat the neck and lower back as the exposed regions they are, particularly in anything loaded or weight-bearing.
• Stop reading a student's range as a measure of their effort. It is mostly a measure of their build.

Reading this is a start; seeing it is different. Watching fifteen people attempt one shape, with a teacher naming why each one lands where it does, teaches more about skeletons in a morning than a chapter does in a week. On our 200 hour yoga teacher training in Rishikesh, anatomy runs as a daily class next to alignment and adjustment for exactly that reason.

Next in the series

The vertebral column gets its own post, because the five regions move so differently from one another: spine anatomy for yoga. For the overview of all seven systems, start at yoga anatomy for teachers.