Reading the body as a system of forces
Watch someone walk into the room — what can you READ? Some teachers can recite every muscle name and still cannot explain why a student's shoulder has hurt for a month. The problem is not that you remember too few muscles. The problem is that 'knowing muscle names' and 'reading force' are two entirely different skills. This lesson is the piece that closes the whole of Stage 1: the six directions of movement, the hinge joints, muscle–tendon–fascia, tension and compression, the core and the breath, the body-wide fascia — all gathered into ONE eye for reading a body. By the end you will look at a shape and know where the force is going, which joint is carrying the load, which muscle is contracting and which lengthening, which link is weak — and you will carry a seven-step checklist into your very next class. You will also meet a truth that baffles the whole teaching community: the painful place is almost NEVER the place with the problem.
🎁 A gift from Tuấn Anh to teachers who want to master the craft.
From 'knowing muscle names' to 'reading force'
Through Stage 1 you have learned 6 separate pieces: the six directions of movement, joints & hinges, muscle–tendon–fascia, tension vs compression, the core and the breath, and body-wide fascia. Today we learn no new piece — we assemble them into one eye for reading a body.
- The real aim: to look at someone standing or going into a shape and read — where the force is going, which joint is carrying the load, which muscle is contracting, which is lengthening, which link is weak or compensating.
- The shift in thinking: from 'knowing muscle names' (a list to memorise) to 'READING movement & force' (a skill you use in the middle of a class). These are completely different skills — many teachers can recite muscle names and still, standing in front of a class, cannot tell which muscle is contracting.
What this gives you: relief from the pressure to memorise muscle tables; instead you have a repeatable frame of questions, usable even when a student goes into a shape you have never analysed.
The root principle of every movement-anatomy text: 'form follows function' — structure reflects the job, and the body is an integrated whole. Bone, muscle, breath, organs and mind are interwoven and affect one another at every moment.
- We separate the parts only in order to study them — while always knowing each part is only one piece of a larger whole.
- The consequence for reading force: reading a shape is never reading a single muscle, but reading how the parts transmit force to each other.
What this gives you to correct: drop the habit of 'adjust where it hurts'. When a student's shoulder hurts, the right question is 'what force is piling up at the shoulder, and which link does it originate from?'
Contract, release and lengthen the RIGHT muscles, and the bones will line themselves up.
Don't memorise a list of muscles — read where the force goes, which joint carries it, which muscle contracts and lengthens.
Reassembling the 6 foundation pieces
Before the detail, look at the whole of your toolkit:
- 1. The six directions of movement (3 planes): the 'coordinate system' — for naming which way the force is going (flexion and extension in the sagittal, adduction and abduction in the frontal, rotation in the transverse). 'Every movement is a combination of the 6 elementary movements.'
- 2. Joints & hinges: the shape of the joint decides in advance which forces are possible — ball and socket (shoulder, hip) a large range, a hinge (knee, elbow) one axis only and stable. Expecting rotation from a hinge joint is a source of injury.
- 3. Muscle–tendon–fascia: muscle makes the force, tendon transmits it into bone, fascia spreads it throughout the body.
- 4. Tension vs compression: along a line of force, ask which tissue is being compressed (bone, disc, cartilage) and which is under tension (muscle, tendon, ligament).
- 5. The core and the breath: the deep core holds the axis; the diaphragm is the 'engine' of the breath — and the breath reflects the whole body's load.
- 6. Body-wide fascia: a continuous web — pulling in one place affects the whole chain at a distance.
What this gives you to teach with: print these six lines and stick them on the wall. Whenever you are stuck, scan back over them to see which piece you have missed.
Every piece you have learned now has a ROLE in reading force — not one of them is spare.
The line of gravity — the coordinate system for reading
Before examining any muscle, set up a coordinate system: the line of gravity dropping straight from the crown of the head to the ground. Seen from the side, the ideal anatomical plumb line passes through the ear → shoulder → hip → knee → ankle — this is a standard reference line for comparison, varying with each person's structure, not a constant into which every body must be forced.
- The first question when reading anybody: 'where is the weight falling?' In an optimal standing position the load falls onto the heel and the sole, the bones carry it, and the muscles are all but at rest.
- Try it in your own body: stand up, release, close your eyes for a few seconds — feel whether the weight falls towards the front of the foot or towards the heel. That is the first input into the reading frame.
What this gives you: film a student standing side-on and draw a vertical line on the screen — you 'see' at once where the deviation is, with no equipment needed.
This is the question teachers often ask: 'does the plumb line apply to every body type?' The answer: the plumb line is a reference for comparison, NOT a rigid mould.
- Each person has a different inborn ratio of collagen to elastin and a different bone shape → a different range of movement and a different 'home axis'.
- The aim is not to reach a fixed 'standard' position but to help a student move in and out around a 'home base' that is balanced for their own structure.
What this gives you to correct: don't force everyone into one magazine mould. Use the plumb line to spot obvious deviations (the head carried forward, locked knees), and then respect each person's own bones.
The bones stacked with the weight falling towards the HEEL; the muscles only 'buzzing' lightly to hold the balance.
Set up the ear–shoulder–hip–knee–ankle plumb line BEFORE examining any joint.
Stacking the joints: does bone carry it, or does muscle grip?
'Asana' originally means 'a comfortable position, without effort'. We approach effortlessness by stacking the long axis of the bone in line with the direction of gravity.
- On the axis: the bones stack like wedges on one another, the curves 'absorbing shock like a spring' → BONE carries the load and muscle can rest.
- Off the axis: the bone is not in a load-bearing position → MUSCLE has to grip continuously to hold it, and wears out.
- The procedure in one line: 'use muscular force to BRING the bone into the load-bearing position; once it is there, the muscular effort drops sharply.'
Demolishing a major misunderstanding: many people imagine 'only constant gripping makes you strong'. Wrong — constant gripping is a sign of being off the axis. The aim of Tadasana is 'to activate as few muscles as lightly as possible'.
What this gives you to correct: when a student shakes or tires early in a static shape, don't say 'try harder' — look for the off-axis link that is making a muscle compensate.
With the head carried forward, the load on the neck rises progressively, up to fivefold at a large angle of flexion. The neck extensor group (splenius capitis and cervicis) has to contract isometrically to compensate → inflammation and excessive strain, causing pain.
- This is the clearest force-reading switch there is: the head stacked over the body → minimal muscular effort; the head carried forward → the neck 'gets heavier' and the muscle wears out.
- The remedy: greater postural awareness + gently pressing the head back into a hand or a wall for a few breaths.
What this gives you: an extremely easy illustration for teaching students why 'keeping the head over the body' matters — not for appearance, but to reduce the load fivefold.
A further dimension to stacking: the human body is not a stack of hard bricks. Because the fascial web covers everything, this is a dynamic structure in which the bones FLOAT within a continuous soft-tissue web that both stretches and holds its integrity — called biotensegrity (from Buckminster Fuller's 'tensegrity').
- The rigid parts do not actually touch but are separated and supported by the soft parts under tension.
- The consequence for reading force: don't picture the body as a brick tower; picture a tension–compression system in which the balance of the whole web decides the stability.
What this gives you: it explains why a small adjustment at the foot changes the whole standing posture — the whole web shifts, not one joint.
Carry the head forward and the load on the neck rises progressively — UP TO FIVEFOLD at a large angle of flexion.
On the axis → BONE carries it and muscle rests. Off the axis → MUSCLE grips and wears out all session.
Which TISSUE is the force landing on?
Every tissue has a map of its limits (the stress–strain curve):
- The elastic zone: remove the load and the tissue returns to its original length — safe.
- Past the yield point → the plastic zone: the tissue does not return; 'clinically, this is a TEAR'. The extreme is complete rupture.
The golden rule when reading tension: 'in a stretch you must feel it in the MIDDLE OF THE MUSCLE BELLY, NOT near the joint.' If there is sharpness, burning, numbness or pain, or you have to hold your breath or grimace → you are over-stretching, and the force is landing in ligament or tendon (very inelastic, and easily left permanently unstable).
Try it now: fold forward a little and stop at the 'comfortable stretch' point — notice that the sensation sits in the middle of the back of the thigh (the muscle belly) and not right by the sitting bone or behind the knee. That is precisely the boundary you teach students to find for themselves.
What this gives you to correct: teach students to tell 'a comfortable stretch in the muscle belly' from 'sharpness near the joint' — this is the most important safety brake you can hand them.
Combined with the rule of 'no bone-against-bone compression', especially at the lower chest when arching (in Ustrasana, for instance).
- Load carried as tension in soft tissue = safe; the tissue absorbs it and springs back.
- Load that has piled up as hard compression of the joint = a risk to cartilage and disc.
- Tendon & ligament stretch only slightly and do NOT contract — pulled past their resting length they usually do not return (bound up with hypermobility & chronic joint pain).
What this gives you: when you see a student 'cranking the arch to the maximum to go deeper', ask whether they are creating space or pressing two bones together — that is the line between opening and injury.
A stretch must be felt in the MIDDLE OF THE MUSCLE BELLY. Sharpness, numbness or burning near the joint = you are pulling on tendon and ligament.
The four muscle roles & the three kinds of contraction
This is the tool for answering 'which muscle contracts, which lengthens':
- Agonist (prime mover): the muscle CONTRACTING to make the movement at the joint.
- Antagonist: the muscle on the opposite side, which must LENGTHEN for the agonist to contract. The model example: flexing the elbow → the biceps as agonist contracts, the triceps as antagonist releases; extending the elbow → the roles swap.
- Synergist: fine-tunes the movement and blocks unwanted movement — especially when the agonist crosses two joints.
- Stabiliser (fixator): holds the bone at the agonist's origin still, creating a firm base.
The hinge principle: a muscle's role depends on the movement being made — flexing the knee, the hamstrings are the agonist and the quadriceps the antagonist; extending it, the reverse. A subtle point: 'a muscle being lengthened' does NOT mean 'a muscle at rest' (the adductors in Trikonasana are being lengthened while also holding the balance).
What this gives you: instead of remembering 'what muscle X does', ask these four questions of the specific shape in front of you — and you read at once which muscle contracts and which lengthens.
The SAME muscle in the SAME shape plays different roles in three phases:
- Concentric: the muscle SHORTENS, creating a shortening movement against gravity — the quadriceps pushing you up out of Warrior II (extending the knee).
- Eccentric: the muscle contracts WHILE LENGTHENING, braking and controlling the load — the quadriceps restraining the speed of the knee bending; lowering slowly; walking downhill. This is the kind that builds strength fastest.
- Isometric: the muscle produces tension without shortening, and the bone does not move — holding still under engagement. Most of the muscular work in static yoga is isometric — and this is precisely the phase in which a muscle will WEAR OUT if you are off the axis.
An example with all three phases: going into a shape = concentric; holding = isometric (engaged under a static load); coming out = eccentric.
Try it in your own body: stand up and then sit back down into a chair very slowly — the lowering part is the quadriceps contracting eccentrically, and you will feel it 'heavier' and shakier than the standing-up part. That is why going down stairs leaves you less out of breath but loads each muscle fibre harder and brings on more soreness (DOMS).
What this gives you: understanding why a student tires in the holding phase rather than the entry phase — and why going down (eccentric) is 'heavier' than going up.
This is the anatomical root of 'compensation' thinking:
- A single-joint (monoarticular) muscle: crosses 1 joint → moves or stabilises that one joint (the iliacus).
- A multi-joint (polyarticular) muscle: crosses several joints (the psoas, QL, rectus femoris) → and is where force travels along a chain. Contracting it produces movement at both joints unless another muscle holds one stable → forcing the neutralising muscle to GRIP harder to keep the axis.
- The lever system: the joint = the fulcrum, the muscle = the force, the bone = the load. The LONGER the lever, the harder the muscle must work. 'The further the arm reaches, the heavier it is' — in Warrior III with both arms fully extended, say → a long lever → the muscles supporting the spine grip considerably harder.
What this gives you: to reduce the load for a weaker student, shorten the lever (bring the arms in towards the body) rather than making them grip harder. Hold that thought — because in a moment it will explain the strange business of 'pain at the knee but the culprit at the hip'.
EVERY muscle CAN be agonist, antagonist, synergist and stabiliser — the role depends on the movement.
The same muscle CHANGES role with the movement — so ask: which one contracts, which lengthens, which holds.
The five-step reading procedure (base → top)
Going from the whole body down to the detail — a properly controlled 'zoom':
- Step 1 — the line of gravity & the point of support: 'where is the weight falling? Where is the support (the feet, the hands)?' Set up the plumb line first.
- Step 2 — on the axis vs off it: 'which joints are stacked (bone carrying), and which are off the axis (muscle gripping to compensate)?'
- Step 3 — the most heavily loaded joint: 'pick the joint taking the greatest load; which of the six directions is it opening or closing in? Is it a hinge or a ball and socket?'
- Step 4 — contracting / lengthening / holding: ask the three core questions — 'which muscle is GETTING STRONGER (contracting)? Which is BEING LENGTHENED? Which is HOLDING STABLE?' And: is it contracting concentrically, eccentrically or isometrically?
- Step 5 — the weak or compensating link: trace along the fascia — 'which off-axis place is making which muscle grip and wear out? Where does the pain (if any) show, but where is its source?'
What this gives you to teach with: run it in this exact order so you miss nothing and don't look about at random. The whole body first, the detail second — 'context first'.
An implicit law running through all five steps: the joint reaction force (muscle contraction + gravity creating an opposing force across the joint surfaces) must be spread over the largest possible area.
- Joint congruency: a congruent joint distributes the force evenly; out of congruency → the stress concentrates on a SMALL area → damaging cartilage and causing degeneration.
- The principle: use the joint WITH the large range to SPARE the joint with the small one.
What this gives you to correct: going into the deep hip-rotation shapes, remind students to take the rotation from the hip (the ball and socket) and never to 'twist' at the knee (a hinge) — that is the most practical joint protection there is.
Scan from the WHOLE BODY into the detail: the line of force → the stacking → the loaded joint → contracting and lengthening → the weak link.
A demonstration: reading a real shape
Worked example one for 'the problem is not where the symptom is':
- The chain of deviation: TIGHT hamstrings → pulling the pelvis into a backward tip → pulling on the lumbosacral fascia → the low back losing its natural curve and being 'dragged' into a round. The student feels pain in the low back, but the source is in the back of the thigh.
- Fixing it at the ROOT: bend the knees a little to release the hamstrings → engage the iliopsoas to tip the pelvis forward and restore the lumbar curve → hold the pelvis there with the iliopsoas, and only then engage the quadriceps to extend the knee and take the hamstrings to their limit.
What this gives you: next time a student complains of 'tightness or pain in the low back in Down Dog', don't adjust the back — ask about the hamstrings and the pelvis first.
Worked example two, applying the whole toolkit to one shape:
- Going in (concentric): the hip flexors (rectus femoris, sartorius, iliopsoas) + the spinal extensor group as agonists, contracting to lift the legs and straighten the torso.
- The antagonists (lengthening): the hip extensors (glutes and hamstrings) + the abdominals that flex the spine.
- The stabilisers (fixators): the psoas + transversus abdominis + QL holding the low back and pelvis (here the rectus and obliques are stabilising rather than flexing).
- Coming out (eccentric): those same hip flexors contracting eccentrically to brake the legs as they lower.
- The muscle being lengthened: the hamstrings.
What this gives you: this is the frame you can apply to any shape and any person — you need not know it in advance; you only need to run the five questions.
A very vivid dynamic example, with the hamstrings:
- Going into Warrior II (bending the knee): the hamstrings contract concentrically.
- Moving on into Triangle (extending the knee): the hamstrings contract eccentrically — lengthening while still working to brake.
The same muscle, the same flow of movement, but the kind of contraction reverses according to the direction of the movement and of gravity.
What this gives you: when you design a sequence, knowing which stretch has the muscle 'braking' (eccentric, effortful and tiring) tells you where to remind students to go slowly and with control.
Down Dog: the knot in the hamstrings, the symptom in the low back. Navasana: reading all 4 roles + all 3 phases.
Why the pain is NOT where it hurts
This is the answer to 'why does adjusting the ankle open up the hip's range':
- Fascia is a thin continuous web covering every muscle and organ — 'like the white pith of an orange: separating the parts but integrating the whole'.
- A muscle's contractile force is transmitted into the fascia and spreads out — this is 'the reason a shape acting on the foot suddenly frees a tight shoulder'.
- Thomas Myers mapped 12 myofascial meridians (Anatomy Trains) transmitting force throughout the body; and sensory nerves lie all through the fascia (more than in muscle).
Demolishing a misunderstanding: the body is NOT a set of separate lumps to be 'adjusted where it hurts'. It is an interlinked tension–compression system — change one point and the whole chain changes.
What this gives you: when one stiff point refuses to open, try intervening at the other end of the fascial chain (the foot, the ankle, the shoulder) — it often opens the range unexpectedly.
The most important paradox in the lesson:
- When a deviation persists, the muscle and fascia on the lengthened side still contract chronically to support it — Thomas Myers calls this 'locked long'; the other side is 'locked short' and becomes weak.
- The paradox: the discomfort is usually felt on the long side, but unless you open the short side the balance is never regained — 'stretching the long, painful side ONLY makes it worse'.
- Referred pain from compression: a chronically tight pectoralis minor compresses the brachial plexus → pain or numbness down the arm; carpal tunnel syndrome shows in the fingers but the compression is at the wrist. The pain is peripheral, but the source of compression is closer to the trunk.
Demolishing a misunderstanding: 'tight hamstrings mean weak or stiff hamstrings' — wrong; they may be being pulled because the pelvis is tipped by some other link. Treat the wrong place and it never resolves.
What this gives you to correct: when you adjust exactly where it hurts and nothing improves, trace the nerve path or the fascial chain back to the source — don't just treat where it shows.
The classic example of congruency: the knee is a heavily loaded hinge, but its health depends on the suppleness of the hip and the alignment of the ankle.
- 'When the hip or the ankle is too tight, weak or out of line, the KNEE SUFFERS because it has to COMPENSATE.'
- Demanding a large external rotation (as in the deep cross-legged seats) that the hip will not give → the force is taken from the knee → congruency is lost → the structures inside the knee are damaged. The pain is at the knee; the cause is at the hip.
What this gives you: a student with knee pain in a cross-legged seat — don't just pad the knee and leave it; open the hip and correct the ankle.
A tight pectoralis minor compresses a nerve → pain down the ARM, even though 'the trouble' is at the chest and shoulder.
The painful place is usually only where the force PILES UP. The source is at a weak or compensating link somewhere else.
The body-reading checklist — 7 questions
A card for immediate use — run it in stacking order, from the BASE to the TOP:
- 1. THE BASE & THE AXIS: are the bones stacked like wedges? Is the weight falling towards the heel? Is the pelvis neutral ('the bowl of water not spilling')? Does the spine keep its four curves (neck in, chest out, low back in, sacrum out)?
- 2. THE LOADED JOINT: which direction does each joint allow (hinge vs ball and socket)? Is it stacked so BONE carries it (the knees 'evenly stacked', not locked)? Where is the load piling up?
- 3. CONTRACTING / LENGTHENING / HOLDING: which muscle is contracting (agonist), which lengthening (antagonist), which assisting (synergist), which holding (fixator)? Contracting concentrically, eccentrically or isometrically?
- 4. WHERE IS THE FORCE LANDING: tension in the middle of the muscle belly (safe) or piling into tendon and ligament near the joint (risky)? Has it passed the yield point, or become bone-on-bone compression?
- 5. THE WEAK OR COMPENSATING LINK: which off-axis place is making which muscle grip and wear out? (tech neck ×5 load; locked long and short; the knee suffering for the hip and ankle).
- 6. THE BREATH & THE CORE: is the shape strangling the diaphragm? (a shallow or ragged breath = overload). Is the deep core holding the axis?
- 7. THE WHOLE-BODY CHAIN: remember fascia transmits force throughout the body; the pain may NOT be at the damage → trace the chain of force back to the SOURCE.
What this gives you to teach with: this is the thing you take into your class in the very next session — no equipment and no thick manual needed.
Reading the theory is not enough — feel it in your own body:
- (a) Read yourself: stand side-on to a mirror or film yourself, draw the plumb line, and run the seven-question checklist on yourself. Write down 2 places where you are off the axis.
- (b) Read a practice partner or student: watch them standing still for 30 seconds and write down 3 things you read — where the force piles up, which joint is off the axis, which muscle appears to be compensating.
- The sensing layer (proprioception): remember that the 'sixth sense' reports the body's position — the more you practise, the more finely you (and your students) read the body. Read the proprioceptive feedback too, not only the visible form.
What this gives you: turn the checklist into a reflex. After a few dozen readings you 'see it in five seconds' — like a doctor reading a scan by eye.
Anchor the pelvis → lengthen the spine → open the chest → lift → balance: read from the base to the top.
Print it and stick it up. Scan BASE → TOP, and always close with the question 'where is the force coming from?'
You have just learned the uncomfortable part: a joint on its axis has bone carrying the load and muscle resting; off by a little and the muscle grips and wears out all session without the student ever knowing. And you have just seen — a painful shoulder whose culprit may lie in a shoulder blade dragged down, in a tight pectoralis minor compressing a nerve, or in a rounded breathing posture. So if the painful place is not the damaged place, how do you trace back to the REAL weak link? Why does a quiet deviation at A, months old, erupt as pain at B? And why does the degree of tissue damage on an X-ray sometimes not match the degree of pain a person feels? That is the whole of Stage 2 — where we stop reading a static shape and start hunting the origin of chronic pain. See you in the opening lesson: 'Why the pain is not where it hurts'.
To unlock Lesson 9
Answer all three correctly to unlock Lesson 9.
1. What are the four walls of the “core canister”?
2. On the IN-BREATH, how do the diaphragm and the pelvic floor move?
3. Engaging the core PROPERLY means:
The road — 31 lessons · 4 stages
You are on Lesson 8. Each lesson opens one real question about the body — understand it, and you practise & teach that much more soundly.
- 1The spine — the axis of all movementAvailable
- 2The six directions the spine movesAvailable
- 3Which muscles each spinal direction uses (SHORTENING ↔ LENGTHENING)Available
- 4Why years of practice still won't get you into the lotus (tension vs compression)Available
- 5Every joint its own kind of hinge (bone – joint – cartilage – ligament)Available
- 6Muscle, tendon, fascia: the factory that makes & transmits forceAvailable
- 7Does stretching really make a muscle "longer"?Available
- 8The core is an "inflatable corset" — breath · diaphragm · pelvic floorAvailable
- 9One shape at the foot frees the shoulder (fascia)Available
- 10Why one cue produces a different shape in every bodyAvailable
- 11Reading the body as a system of forces (putting it together)You are here
By the stacking principle, what happens when a joint is stacked IN LINE with the line of gravity?