Muscle – Tendon – Fascia: the trio that makes force, transmits it, and weaves the whole body into one
Why can you hold Warrior II without the leg collapsing? Why do the hamstrings stay tight however diligently you pull on them? And why does a student's painful shoulder have its root all the way down in… the sole of the foot? All three questions have ONE trio behind them: muscle makes the force, tendon transmits it, fascia joins everything into one living web. This lesson starts with the big picture and only then looks into each layer — you need no anatomical background, only a body that practises and some curiosity. Don't be daunted by the terms: we build step by step, and every idea you finish is something you can touch and feel on the mat straight away.
🎁 A gift from Tuấn Anh to teachers who want to master the craft.
The force-making and force-transmitting trio — the whole view before the detail
Every movement around a joint is caused by force, and the force is made by muscle contracting. But muscle does not move bone directly — it has to transmit the force along a chain:
- The muscle contracts → force arises in the belly of the muscle.
- The fascia surrounding the muscle receives and conducts the force.
- The muscle–tendon junction passes it on to the tendon.
- The tendon pulls the bone → the joint moves.
Three cords with clearly distinct jobs — don't confuse them:
- TENDON joins muscle → bone; its job is TRANSMITTING FORCE.
- LIGAMENT joins bone → bone; its job is STABILISING the joint.
- FASCIA wraps and joins the whole body into a myofascial web, both transmitting force and reporting sensation.
What this gives you: when you cue 'engage the thigh to straighten the knee', you are describing exactly this chain. A student with tendon pain (wrist, patella) is in a quite different situation from one with muscle pain — because the two tissues heal at very different speeds (the tendon section will make that clear).
The body has three kinds of muscle tissue, but only one makes a yoga shape:
- Skeletal (striated) muscle: attached to the skeleton, contracting at WILL, creating all movement. The whole of Lesson 6 is about this kind.
- Smooth muscle: in the walls of the organs and the blood vessels — contracting involuntarily (under stress, for instance, the vessels constrict to send blood to skeletal muscle).
- Cardiac muscle: in the heart only, pumping continuously for a lifetime.
The body has around 640 skeletal muscles, making up roughly 40% of body weight. The distinctive property of muscle tissue is its capacity to CONTRACT / SHORTEN to produce force.
What this gives you: when a student asks 'does yoga affect the internal organs?' — yes, but indirectly (through compression, massage and the autonomic nervous system); what we actively control in a shape is always skeletal muscle.
Movement does not arise by itself — it is a chain of transmitted force: muscle contracts → fascia → tendon → bone → the joint turns.
Muscle = the engine that makes force · tendon = the cable that transmits it to bone · fascia = the web that wraps and joins the whole body. Hold that metaphor and every detail that follows has somewhere to hang.
How muscle is built and how it contracts — zooming in, then setting it moving
By the end of this section you will be able to explain to a student 'what is inside the thigh' without a single anatomy slide.
Imagine taking a magnifying glass gradually into the front of the thigh:
- The muscle (the whole mass you can feel)
- → Large bundles → smaller bundles (fascicles)
- → A muscle fibre = one muscle cell, the functional contracting unit
- → Myofibrils running lengthwise inside the fibre
- → Sarcomeres = the smallest contracting unit, bounded at each end by a Z-disc
- → inside which are the THIN filaments = actin and the THICK filaments = myosin.
It is the regular arrangement of actin and myosin that creates the striations for which skeletal muscle is also called 'striated muscle'. Muscle also has NON-contracting components: the fascial sheaths wrapping each level, plus the muscle–tendon junction.
What this gives you: an image of 'the large containing the small' to explain to students without drowning in terminology. Have them squeeze the thigh and say: 'in your hand is a bundle of bundles.'
This is the answer to the classic teacher's question: 'what does actin and myosin sliding over each other actually mean?'
- A nerve impulse reaches the muscle and, with calcium present, 'unlocks the block' on the actin filament.
- Myosin (the thick filament) reaches out and forms a cross-bridge onto the actin.
- Myosin pulls the actin sliding inwards → the two Z-discs draw closer → the sarcomere shortens → the whole muscle contracts.
An easy metaphor to teach with: many hands hauling on one rope in a 'ratchet' fashion — pull, grip again, pull on. This is an ACTIVE, ENERGY-CONSUMING (ATP) process — which is why holding a shape for a long time makes you tired.
Bonus — states & control: a muscle is always in one of three states: contracting / released / being stretched. A motor unit = one neuron plus all the muscle fibres it supplies; we can train it to be 'quiet' so as to release genuinely — the foundation of deep relaxation.
What this gives you: explaining why 'holding a Plank' shakes and burns — not a weakness, but the cross-bridges burning energy continuously.
Muscle contraction is no miracle — it is millions of myosin 'hands' hauling on an actin rope, ratchet-fashion.
A muscle is a 'bundle of bundles': large bundles → small bundles → fibres → myofibrils → actin & myosin. Contracting = myosin cross-bridges pulling actin to slide inwards, costing energy and needing calcium.
Three kinds of contraction — one muscle, within one breath, working in three different ways
When it is stimulated, a muscle always tries to pull its two attachments closer — but does NOT necessarily shorten. From which come two branches:
- ISOTONIC contraction: the contraction CREATES movement → the muscle's length CHANGES. It divides further into concentric and eccentric.
- ISOMETRIC contraction: contracting but creating NO movement → the length is UNCHANGED.
Hold that frame and you can derive the 'three kinds of contraction' yourself, without learning them by rote.
Concentric ('towards the centre'): the two attachments come closer and the muscle SHORTENS, producing force against gravity — the muscle group that 'GOES INTO' the shape. This muscle is the agonist (prime mover).
- The hamstrings contracting to flex the knee on the way into Warrior II or Setu Bandha.
- The biceps contracting to lift a weight to the shoulder.
- The abdominals contracting to lift the torso in a curl.
The right cue: 'actively engage [muscle X] to come into the shape' — this is the moment to say 'activate' and 'engage'.
Eccentric ('out from'): the muscle fibres 'pay out' UNDER CONTROL to slow a movement that gravity would otherwise make too fast. The muscle is producing force while LENGTHENING — the role of a brake.
- Lowering into Chaturanga with control: the chest and arms are working eccentrically and very hard — not 'resting' at all.
- The quadriceps lengthening as the knee bends into Virabhadrasana II, or walking downhill, braking the body.
- Sitting slowly down into a chair, lowering a weight slowly.
⚠️ Demolishing two misunderstandings:
- 'Lowering down is the muscle resting' → WRONG. That is when the muscle is under its highest load.
- 'Aching the next day (DOMS) is from lactic acid' → WRONG. Lactic acid clears within hours. DOMS is micro-damage to muscle and connective tissue, clearest after eccentric work — because the force lands on fewer muscle fibres. It is a benign ache, not an injury; and eccentric work makes muscle stronger faster.
What this gives you: call 'control it as you lower', 'don't let it drop' instead of 'relax down'; and reassure students that aching after a session with a lot of slow lowering is normal.
Isometric ('iso' = same, 'metric' = length): the muscle's tension rises but its length does NOT change, and the joint does NOT move — the muscle is HOLDING / FIXING the shape. This is the commonest kind of contraction while holding an asana still, and a genuine form of strength training.
- Rectus abdominis holding the torso in Navasana (the fixator role).
- Holding the bent knee still in Virabhadrasana II.
- Many postural muscles contract isometrically by reflex: standing upright, the calf muscles keep us from falling forwards and the muscles at the back of the neck hold the head.
An interesting detail: merely 'imagining yourself stronger' raises the measurable force without the muscle moving at all.
What this gives you: name it correctly — 'this is the holding phase; engage evenly, breathe evenly'; don't let students imagine a held shape is 'a rest'.
When you 'relax' and lower yourself down, the muscle is working HARDEST — the braking paradox that 90% of students never know.
Concentric = shortening, going into the shape. Eccentric = lengthening while still working, braking on the way down. Isometric = holding still. Which one have you been naming wrongly all session?
Anchors & coordination: origin, insertion and the four roles of a muscle
The origin = the NEAR attachment, onto the more fixed bone. The insertion = the FAR attachment, onto the more mobile bone. Between them is the belly, holding the contracting fibres. The attachment points are usually the tendons themselves.
- For example: rectus femoris has its origin at the anterior inferior iliac spine (AIIS) and its insertion through the quadriceps tendon onto the patella.
In yoga it is often REVERSED: we hold the FAR end fixed (hand or foot pressing the floor) and then draw the origin towards it:
- Pectoralis major in Vasishthasana → drawing the chest towards the supporting hand.
- The adductors in Janushirshasana → not moving the leg but rotating the pelvis towards the leg.
Modern anatomy tends simply to say 'the proximal / distal attachment'.
What this gives you: explaining why the same iliopsoas flexes the hip when standing and pulls the torso forward when lying down — the only difference is which end is fixed.
Within one movement, muscles divide into four roles:
- Agonist: contracting concentrically to make the movement.
- Antagonist: on the other side of the joint, lengthening, or contracting eccentrically, to let the agonist work.
- Synergist: assisting, fine-tuning, preventing unwanted movement — especially when the agonist crosses several joints.
- Fixator (stabiliser): holding the bone at the origin still to create a firm base.
The core principle — the roles are RELATIVE and swap with the movement: if the biceps flexing the elbow is the agonist then the triceps is the antagonist; when the triceps extends the elbow it is the other way round. A large enough muscle even acts as its own antagonist (the front deltoid draws the arm forward, the rear deltoid draws it back).
Often a muscle is being stretched and having to stabilise at the same time: the adductors are stretched in Trikonasana while still holding the standing position — and this is exactly yoga's act of being stable and free at once.
What this gives you: when you analyse a shape, ask yourself: which muscle is getting stronger (contracting), which is being stretched, which is holding — three questions and you have 'read' the shape.
Reciprocal inhibition: when you contract the antagonist, the nervous system automatically tells the target muscle to release, so the movement happens smoothly.
- In Paschimottanasana: actively contract the quadriceps (the front of the thigh) → the hamstrings are told to let go → a deeper and safer stretch.
- Pressing up into Chaturanga: contract the triceps quickly → the biceps releases automatically.
Co-contraction: when extra stability is needed, we deliberately hold the target muscle lightly as well, to avoid over-stretching and injury.
What this gives you: replace the vague 'try to stretch deeper' with a cue that has a mechanism: 'engage the front of the thigh lightly and let the back of the thigh soften by itself'. This is active stretching, as distinct from the passive stretching of hanging on your own weight (Uttanasana).
To make the back of the thigh release, don't call 'stretch deeper' — say 'engage the front of the thigh'. That is reciprocal inhibition.
Origin = the fixed attachment; insertion = the mobile one. In yoga we often REVERSE them. One muscle can be agonist, antagonist, synergist or fixator — DEPENDING on the movement.
Tendon — the force-transmitting cable, poorly supplied with blood so slow to heal, and the Golgi 'safety brake'
By the end of this section you will know why 'stretching muscle' is safe while trying to 'stretch tendon' is playing with injury.
Tendon is a cord or band of DENSE connective tissue, made of parallel collagen bundles → extremely good at taking tensile load, but inelastic. In essence: the fascia wrapping the muscle converges and extends beyond the end of the muscle into a round cord (a tendon) or a broad flat sheet (an aponeurosis), and then merges into the periosteum.
- Function: joining muscle to bone, transmitting the contractile force to move the joint. The patellar tendon joins the quadriceps to the tibia to extend the knee.
- It carries sensory nerves reporting tension and joint position to the brain.
- It stretches little and does NOT contract — pulling it too long is an injury; past the 'yield point' it does not return to its resting length.
What this gives you: remind students to feel the tension in the belly of the muscle, not near the joint or the tendon. Practising in a warm room improves the pliability of tendon and ligament.
Because tendon has few blood vessels, it heals very slowly — a tendon injury is measured in months and easily recurs if you go back too soon. This is why tendon pain (the wrist in Chaturanga, the patellar tendon in a deep squat) is so uncomfortable and so persistent.
⚠️ A misunderstanding to demolish: 'rest a sore tendon completely until it is better'. In reality most tendons recover better with GRADUALLY INCREASING, CONTROLLED LOAD; absolute rest usually leaves a tendon weaker and slower to heal.
What this gives you: with a student who has tendon pain, point them towards 'reduce the load, then build it back gradually' rather than simply advising 'rest' — while making clear you are not a substitute for medical diagnosis; persistent pain needs a professional.
The Golgi tendon organ is a receptor sitting within the tendon, registering the level of tension in the muscle. When the tension peaks, it sends a protective signal, inhibiting the contraction and the resistance → the muscle releases deeply (that pleasant 'ahhh' feeling). Its effect lasts a while → which makes it very useful when holding a shape for thirty seconds or more.
This is the basis of assisted stretching / PNF — the technique of alternating contraction and stretch to go deeper more safely. A model procedure for the hamstrings (lying on the back, with assistance):
- Lift the leg to just below the maximum stretch threshold, extend the knee using the quadriceps (setting off reciprocal inhibition).
- Press at about 80% of effort, contracting the hamstrings for about ten seconds → the Golgi organ receives the tension stimulus and orders a further release.
- Reduce the effort to about 20% and slowly take the leg deeper (moving gently).
- Repeat for a few rounds; the range increases gradually.
⚠️ A safety note: contract the muscle being stretched only LIGHTLY, to avoid loading the joint excessively.
What this gives you: understanding why 'contract–hold–release' works, so you use it at the right moment, and telling it apart from the muscle spindle's stretch reflex (next section).
Within the belly of the muscle are muscle spindles — specialised fibres sensing the amount and the SPEED of a stretch. Stretched FAST, they trigger the stretch reflex: ordering the muscle to CONTRACT in self-defence (like the knee-jerk reflex to a tap of the hammer — the signal goes straight to the cord and back, with no time for the brain to join in).
Because of this reflex, bouncing while stretching is counter-productive: the muscle you mean to lengthen contracts instead, leaving you stiffer the next day and more liable to tear. Conversely, the spindle's response fades if the stretch is SLOW and steady → so go into a shape gradually to pass the reflex safely.
Telling them apart quickly: the Golgi organ is in the tendon and responds to tension (helping release). The muscle spindle is in the muscle and responds to the speed of stretch (forcing a contraction).
A sore tendon takes a long time to heal not because you are weak — but because it has almost no blood supply.
Tendon = parallel collagen bundles joining muscle to bone, excellent under tension but inelastic, POORLY SUPPLIED WITH BLOOD so slow to heal (months). 'Stretch muscle; don't try to stretch tendon.'
Fascia — the living web joining the whole body, and the reason pain in one place comes from tension elsewhere
By the end of this section you will understand why opening the hips can cure back pain — and how long to cue a hold for it to reach the fascia.
Fascia is a connective-tissue sheath wrapping and separating each muscle and each organ; a thin film of fluid over it lets the muscle GLIDE on the structure beside it (that is the sheen of muscle in surgery).
- Each muscle is made of many fibre bundles, each separated by a thin membrane called myofascia — like the pith separating the segments of an orange, both separating and integrating.
- Fascia supplies internal structure, support, FORCE TRANSMISSION and is a source of sensory feedback.
- Fascia makes up a considerable part of the mass of a muscle → so its density or softness considerably affects overall flexibility.
The sheets of fascia join CONTINUOUSLY from head to toe — the basis of the body-wide myofascial web. The anatomist Thomas Myers describes 12 myofascial meridians ('Anatomy Trains') transmitting movement and tension throughout the body. Fascia also has more sensory nerves than muscle tissue → so most of what you feel while moving comes from fascia.
The body is a web under tension: pull one corner and the whole sheet shifts. Because the fascial web permeates everything, the body's structure is a tensegrity — the bones 'float' within a continuous soft-tissue web that is simultaneously under tension and supporting (in humans it is called biotensegrity). The rigid parts do not touch each other but are separated and held by the soft parts under tension.
The key consequence for a teacher: because the web is continuous, no movement at one joint happens in isolation. A shape acting at the foot can release tension at the shoulder.
- Uttanasana stretches the whole myofascial sheath of the BACK of the body: the back of the neck → the spine → the hips → the legs → the soles. A restriction anywhere along that line obstructs the forward fold — rolling a ball under the sole for about a minute can free the whole chain.
- Thomas Myers calls the lengthened side 'LOCKED LONG' (usually where the PAIN is) and the shortened side 'LOCKED SHORT' (which becomes WEAK). You must OPEN the SHORT side to rebalance — stretching the long, painful side further only makes it worse.
- For example: an over-short IT band or TFL causes restrictions that spread into the hip, the low back and the knee without hurting at the site itself.
⚠️ Demolishing a misunderstanding: 'where it hurts is where the problem is'. Because the fascial web transmits force throughout the body, the painful point is usually far from the real source of the tension. This is why opening the hips helps back pain.
Myofascia is a MOULDABLE material — like Silly Putty:
- Hold a stretch beyond a brief moment → it adapts to the new length and KEEPS it (the collagen 'creep' phenomenon), rather than springing back.
- It TEARS if stretched too FAST; and it is more pliable when WARM.
The formula for a stretch that reaches the fascia: SLOW – WARM – SUSTAINED, held for 30 to 90 seconds or more (Yin up to 3–5 minutes), with NO bouncing.
WARM — a warm-up heats muscle, tendon and ligament; cold tissue is brittle, and forcing deep before you are warm is the formula for micro-tears. (Hot yoga stretches deeply but only momentarily, and makes it easy to pass the limit → so go slowly even so.)
SUSTAINED — balance strength + suppleness and practise steadily; fascia needs varied movement: long holds (Yin) combined with dynamic work (Vinyasa); and actively loaded stretching (the muscle lengthening while contracting) trains the fascial layers best.
The stress–strain curve sums up the safe limit: the elastic zone, where tissue returns to normal → past the yield point, where tissue does not spring back (damage) → the failure point (rupture).
⚠️ Demolishing two misunderstandings: 'bouncing stretches faster' → WRONG; it triggers the stretch reflex, the muscle contracts, and tearing becomes more likely. 'A foam roller breaks up fascial adhesions and melts knots' → the effect is mainly short-term and comes from a change in the NERVOUS system (reduced pain sensation), not from physically breaking tissue.
What this gives you: this is precisely the scientific reason that distinguishes Yin (long holds to remodel fascia) from Vinyasa — use it to design how long your holds should be.
Ideal fascia is resilient and needs movement to stay healthy. A few factors decide whether you touch your toes easily or not:
- Genetics: each person is born with a different collagen 'blend' (elastin stretches up to 200%, collagen only about 10%).
- Age: collagen stiffens over time; immobility makes it lose its cross-woven lattice (it becomes disordered) — while asana practice helps reorganise the fascia.
⚠️ Demolishing the 'drink more water and you'll be flexible' myth: fascia is mostly water, but you have to MOVE to 'wring' that water through the tissue. Lying still and drinking is not enough — movement is what genuinely hydrates fascia (the 'muscle pump' driving fluid through a one-way valve system, like an internal massage).
The single most important SAFETY distinction: MUSCLE tissue is elastic and well supplied with blood → it stretches and heals BETTER than the connective tissue of a joint (tendon, ligament). So feel the tension in the MIDDLE OF THE MUSCLE BELLY. If the pull is SHARP near an attachment (close to a joint or tendon) → that is a signal you are loading inelastic, poorly supplied tissue that injures easily and heals slowly → bend the knee or come out a little.
What this gives you: the closing line to teach and correct with: 'a stretch in the middle of the muscle is right; a sharp pull next to a joint means stop'.
The body is a web under tension — pull one corner and the whole sheet shifts. Which is why a painful shoulder can begin at the sole of the foot.
Fascia wraps each fibre bundle and joins the whole body continuously into a myofascial web. The bones 'float' in a web under tension (tensegrity). Fascia responds SLOWLY, so a stretch must be slow, warm and sustained.
Fitting the three pieces into one shape — and the summary table for the whole lesson
Navasana shows all three kinds of contraction and all the muscle roles at once:
- GOING IN (concentric): the hip flexors (rectus femoris, iliopsoas), the adductors holding the legs together, the quadriceps keeping the knees straight, and the spinal extensors all shortening to come 'up'.
- HOLDING (isometric): rectus abdominis, the obliques, the psoas and transversus abdominis contracting to hold still, stabilising the torso and supporting the lumbar spine — the fixators.
- COMING DOWN (eccentric): those same hip agonists now lengthening under control so the legs do not crash down.
- BEING STRETCHED: mainly the hamstrings (especially with the knees extended).
What this gives you: use one familiar shape to teach students that 'the same muscle, within one breath, can do three jobs' — and name each phase correctly as you lead it.
- MUSCLE: contracts; elastic and well supplied with blood → stretches well, heals fast; produces force. This is where the stretch should be felt.
- TENDON: joins muscle→bone, transmits force; parallel collagen, inelastic, poorly supplied with blood → slow to heal (months); does not contract. Carries the Golgi organ reporting tension.
- LIGAMENT: joins bone→bone, stabilises the joint; poorly supplied with blood → slow to heal; over-stretching causes joint instability (be careful in pregnancy and with hypermobile people). Protect it by building muscular strength around the joint.
- FASCIA: wraps and joins the whole body; responds SLOWLY (mouldable) → needs long, warm, sustained holds; rich in sensory nerves; transmits force throughout the web.
Three safe-practice principles drawn from this: (1) warm up WARM before any deep stretch; (2) stretch SLOWLY and in a SUSTAINED way, held long enough, with no bouncing; (3) coordinate agonist and antagonist (active stretching) and feel the stretch in the muscle belly.
What this gives you: print this table into your head — it answers nearly every 'it hurts here, what do I do' situation on the mat.
The body is not a bag of separate parts — it is one unified force-transmitting network that you learn to read.
Navasana uses all three kinds of contraction; the whole body is one unified force-transmitting network. Remember the differences between muscle, tendon and fascia in elasticity, blood supply and healing speed, and speed of response.
You now know that muscle makes force, tendon transmits it and fascia joins the whole body — but where must that force finally pass to become movement? The answer lies in the JOINT: where two bones meet, where it is decided how far you can fold, how far you can rotate, and why some people open their hips effortlessly while others are 'locked' tight. In the next lesson we dissect the kinds of joint, their ranges, and which limits come from BONE (unchangeable) and which from SOFT TISSUE (trainable) — so you stop forcing students into shapes their bone structure never permitted.
To unlock Lesson 7
Answer all three correctly to unlock Lesson 7.
1. How does muscle create movement?
2. To lower into Chaturanga strongly & safely, you should:
3. Where should a stretch be felt, properly?
The road — 31 lessons · 4 stages
You are on Lesson 6. 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 forceYou are here
- 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)Available
Lowering slowly and with control into Chaturanga, what are the chest and arm muscles doing?