How The Spine Moves — Six Directions

Picture the spine as the mast of the ship that is your body. It belongs to the axial skeleton (along with the skull and the rib cage) — as distinct from the appendicular skeleton, the arms and legs. Its three mechanical roles:

• Bearing load: holding up the whole upper body and transmitting its weight down into the legs.
• Moving: being a chain of many small jointed bones, it creates a great many movement possibilities — which is what makes yoga so rich.
• Protecting: housing the spinal cord — the bundle of nerves joining the brain to the whole body. The thoracic section, with the ribs, also shelters the heart and lungs.

The spine is at work in EVERY asana — including Savasana, while you merely lie still.

What this gives you: this is the opening line that settles a class — 'controlling a yoga shape is, in essence, controlling this axis'. Once students understand that the spine must be both stable (bearing load, protecting) and supple (moving), they force less and fear less of their own accord.

Seen from the side, a healthy spine is not ruler-straight but curves into a soft S:

• The neck curves in (concave) — to balance the weight of the head.
• The chest curves out (convex).
• The low back curves in (concave).
• The sacrum curves out (the fourth curve, which many people forget).

The terms: curving in = lordosis (neck, low back); curving out = kyphosis (chest, sacrum). In yoga practice people usually speak of the '3 curves' of the three moving regions; in full anatomy there are 4 — both are right.

What are these curves for? They turn the spine into a shock-absorbing spring: absorbing impact, holding your balance, and allowing movement. If the spine were ruler-straight, every step you took would send the shock straight up through the whole body and into the brain.

Demolishing a common misunderstanding: many students (and teachers too) imagine that a 'ruler-straight back' is the beautiful, healthy one. Wrong. A healthy spine is one that KEEPS its natural curves — take the curves away and you take away the shock absorber. That state of keeping the curves is called a neutral spine — the steadiest, most stable alignment there is.

What this gives you to correct: instead of calling 'make your back straight', cue 'lengthen the spine but KEEP its natural curves'. The common deviations to recognise: an over-hollowed low back (hyperlordosis, a sagging back), an over-rounded chest (hyperkyphosis, a stooped back), and a sideways deviation (scoliosis — off to one side, with rotation).

A fact few people notice: each vertebra is really two parts doing two opposite jobs — one half to take the blow, one half to dodge it. Understand that division of labour and you will work out for yourself why 'forcing it' is dangerous.

• The vertebral body (at the front): a short, dense block of bone, shaped like a wedge, stacked on its neighbours to bear load. The further down towards the low back, the larger the body grows, to carry more.
• The vertebral arch (at the back): a ring of bone carrying three projections — two transverse processes at the sides and one spinous process at the back (those are the knobs you can feel running down the back). The stacked rings form the spinal canal, the 'house' that protects the cord.

A key detail: the thoracic vertebrae have additional facets joining them to the ribs — which is why the rib cage attaches to exactly that section.

What this gives you: picturing 'load in front, protection behind' helps you explain why pressing excessively is not good — you are pressing into a structure built to protect the cord, not to take a blow.

The smallest moving unit of the spine is two adjacent vertebral bodies + one disc between them. Each level shifts only a VERY SMALL amount — but add dozens of levels together and the whole spine bends a great deal.

The structure of a disc, pictured as a jam doughnut:

• The thick outer shell = the annulus fibrosus — the 'dough', strong and tough.
• The soft core in the middle = the nucleus pulposus — the 'jam', soft and springy.

The disc is made of fibrocartilage, and both cushions shock and allows movement. In a neutral spine, the load is spread EVENLY across the disc.

What this gives you: understanding the 'fibrous shell around a core' structure is the key to understanding disc injury in the next section. Yoga is good for discs because movement creates space between the vertebrae, reduces pressure and improves the circulation that feeds the tissue — but only when it is practised PROPERLY.

The planes are imaginary 'slices' through the body. There are three, each containing one group of movements — anchor each to a familiar asana:

• The sagittal plane — dividing left from right → contains FLEXION & EXTENSION. For example: Sun Salutations, Downward Dog.
• The frontal (coronal) plane — dividing front from back → for the spine, SIDE-BENDING. For example: Gate pose (Parighasana).
• The transverse plane — dividing upper from lower → contains ROTATION. For example: Revolved Triangle (Parivrtta Trikonasana).

A quick pairing for the spine: flexion and extension ↔ sagittal · side-bending ↔ frontal · rotation ↔ transverse.

What this gives you: with the three-plane map in hand you can design a 'balanced' session — moving the spine in all three planes instead of only folding back and forth. It is a quick way to audit your own class plan.

Why does this region rotate well and that one hardly at all? NOT because the student has 'stiff muscles'. Four structural factors decide it:

1. The shape & size of the vertebrae in that region.
2. The thickness of the disc.
3. The attachment of the ribs (in the thoracic section only).
4. The angle of the facet joint surfaces between the vertebrae.

Factor four is the most important key of all. Each vertebra meets its two neighbours through four facet surfaces (two facing up, two facing down) — gliding joints, which allow only limited movement. The core principle: it is the ANGLE and ORIENTATION of the facet surfaces in each region that decides what movement that region is allowed. The orientation of the facets is like railway track — whichever way the rails run is the only way the train can go, however much you 'want' to go elsewhere.

What this gives you: this four-factor frame is the master key for explaining every regional limit to a student. When someone cannot rotate at the waist, you can explain it immediately: 'because the facets there are not oriented for rotation', instead of letting them blame themselves for being 'not flexible enough' and then force it.

After puberty the sacral vertebrae fuse into a single sacrum — the 'keystone' that forms the firm base for the whole spine. The sacral vertebrae themselves do not move.

But at the sacroiliac (SI) joint — where the sacrum meets the pelvis — there is a slight, subtle, involuntary glide. This is a flat gliding joint, of the very-little-movement kind, prioritising stability.

A safety warning: over-stretching (a deeply folded Paschimottanasana, say) can leave the SI area uncomfortable, because ligament struggles to spring back to its original length → less stability, inflammation, pain. The sacral region moves little but is easily irritated in the advanced shapes: deep folds, strong twists, wide leg positions, backbends.

What this gives you: understanding that 'the sacroiliac base exists to be STABLE, not supple' keeps you from trying to 'open' this area by over-stretching — for the SI, stability is the aim, not range.

Hold this formula as a safety law: compressive force (from flexion) + torsional force (from rotation) happening together is the classic mechanism that tears the annulus and pushes the nucleus out.

Which is why a supine twist is safer than a seated or standing one — it changes the direction in which gravity presses on the disc. Standing, a twist is often unintentionally combined with flexion — and it is precisely that combination of flexion and rotation that raises the risk.

What this gives you to correct: with a student who has a history of disc herniation, avoid sequencing fold-then-twist one after another; favour a lying base, or lengthening the axis before any strong twist. And remember: yoga is NOT automatically good for a herniated disc — folding forward can push the disc towards the nerve root and make it worse, so the shapes have to be sorted rather than taught wholesale.

Running the whole length of the spine are strong ligaments acting as 'brakes', limiting the range to protect the cord and the discs. They can be grouped by function: the anterior longitudinal ligament (running in front of the vertebral bodies) resists excessive extension and arching back; while behind, the posterior longitudinal ligament, with the supraspinous and the ligamentum flavum, resist excessive flexion. What this means for a teacher: the end of the range in flexion and extension is stopped by ligament — forcing past that threshold means forcing into ligament and disc; it is no longer stretching muscle.

And this is why the lesson is called 'Six Directions': because discs are fed by movement that CHANGES DIRECTION, a healthy yoga programme must take the spine through all six directions, within each region's safe range.

Four closing lines that wrap up the whole lesson (usable with any student):

• Create space; don't compress.
• Move the spine as one unified whole to come back to neutral.
• Go through all six directions within the safe range.
• A lying twist is safer than a standing one.

What this gives you: stick these four lines on your class plan — they are the filter for auditing every sequence you design.