8.3 Major Muscles and Types of Contraction

Muscles create and control the shapes bones allow

Yoga Alliance's RYS 200 Anatomy competency asks schools to cover major muscles involved in asana and types of contraction. Independent OpenExamPrep study covers that 200-hour map: the prime movers you will name in common poses, the three contraction types that explain why lowering can be harder than lifting, and the roles agonist, antagonist, synergist, and stabilizer. It is not a Yoga Alliance national exam, not an official muscle-hour table (Yoga Alliance does not publish a required gluteus-maximus minute count), and not a physical-therapy credential.

Bones aim. Muscles produce, control, and hold the joint angles. You do not need origin-insertion flashcards for every fiber. You do need English muscle names, a few Latin group names your faculty uses, and the honesty to stay inside a teacher's scope of practice.

Prime movers in common poses

Name muscles in English first. Palpate only with prior explicit informed consent, and never as a medical exam.

Gluteus maximus is the large posterior hip muscle. Primary actions: hip extension and external rotation; upper fibers can assist abduction.

• Salabhasana (Locust Pose) and Setu Bandhasana (Bridge Pose): concentric hip extension to lift the pelvis or legs.
• Virabhadrasana III (Warrior III): the standing-leg gluteus maximus helps hold the hip in extension, largely isometrically.
• Utkatasana (Chair Pose): often isometric or eccentric control of hip flexion rather than a universal "squeeze the buttocks" cue.
• Urdhva Dhanurasana (Upward Bow / Wheel Pose): hip extension from gluteus maximus plus hamstrings, so five lumbar joints are not the only extenders.

Cue "root the femur back" or "press the back of the pelvis up" rather than "clench" as a default.

Hamstrings are biceps femoris, semitendinosus, and semimembranosus. They extend the hip and flex the knee (the long head of biceps femoris also contributes to tibial external rotation; the medial hamstrings contribute to internal rotation).

• Lengthened under load in Paschimottanasana and Uttanasana (Standing Forward Fold). That is often a flexibility and neural-tension story, not a concentric "use your hamstrings to fold."
• Active hip extension in locust, bridge, and similar lifts.
• Eccentric control when slowly straightening a bent knee in a forward fold.

Sharp posterior-knee or high-hamstring pain is a stop. Do not diagnose a tear.

Quadriceps femoris is rectus femoris plus the three vasti (lateralis, medialis, intermedius). All four extend the knee; rectus femoris also flexes the hip because it crosses both joints.

• Front-leg knee control in Virabhadrasana I and II and Utthita Parsvakonasana (Extended Side Angle Pose).
• Sitting-to-standing and Chair Pose: quadriceps work concentrically to rise and eccentrically to lower.
• An active reach through the heel in a supine hamstring stretch can recruit the quadriceps to set the knee while the hamstrings lengthen—a useful antagonist pairing, not a treatment protocol.

Iliopsoas is psoas major plus iliacus, the primary hip-flexor group. Psoas also attaches to lumbar vertebrae, which is why hip-flexor stories and lumbar stories get tangled in class.

• Navasana (Boat Pose): iliopsoas flexes the hips to hold the boat shape.
• High lunge and Anjaneyasana (Low Lunge): the rear-leg iliopsoas is lengthened; the front-leg iliopsoas helps hold hip flexion.
• Tadasana: over-gripping iliopsoas can drag the lumbar spine into excess lordosis. "Soften the front of the hips" is a tone-down cue.

Do not claim that "releasing psoas" treats anxiety, trauma, or digestion. That is outside teacher scope.

Erector spinae is the posterior column of spinalis, longissimus, and iliocostalis. It extends the spine and can laterally flex it.

• Concentric in Bhujangasana (Cobra Pose) and locust as the chest lifts.
• Isometric in Tadasana and Warrior II to keep the trunk from collapsing.
• Eccentric when slowly lowering from a backbend.

Pair erectors with abdominal control so extension is not a lumbar hinge. Joint stabilization gets its own later chapter; here, know they are the posterior "stand-up" muscles of the trunk.

Trapezius is a diamond-shaped scapular muscle with three functional parts:

• Upper fibers elevate the scapula (and can extend or laterally flex the neck—be careful with "ear toward shoulder" gripping).
• Middle fibers retract the scapula.
• Lower fibers depress the scapula and help upward rotation.

In Down Dog, many schools ask for lower-trapezius depression ("shoulder blades toward the pelvis") rather than upper-trapezius shrugging. In Warrior II, holding the arms is deltoid plus trapezius and serratus teamwork, not trapezius alone.

Serratus anterior runs from the ribs to the medial border of the scapula. It protracts the scapula, upwardly rotates it, and holds the blade on the rib cage (reducing winging).

• Phalakasana (Plank Pose) and Chaturanga: serratus keeps the space between the shoulder blades from collapsing into a sinking chest, and it is the missing piece when the only cue is "squeeze the blades together."
• Bakasana (Crow Pose): protraction helps the trunk rest on the upper arms.
• Down Dog: upward rotation lets the arms go overhead relative to the scapula.

This is 200-hour gold. Many "shoulder trouble in vinyasa" stories are load plus poor scapular control. You address that with regressions, props, and clearer action cues—not with a rotator-cuff diagnosis.

Deltoid (anterior, middle, posterior) is the bulk of the shoulder cap. Middle fibers abduct the humerus; anterior fibers flex and internally rotate; posterior fibers extend and externally rotate.

• Warrior II arms: mostly middle deltoid, with supraspinatus helping to initiate, plus scapular upward rotators.
• Overhead or side-arm holds in standing poses.
• Chaturanga: anterior deltoid and pectorals help control the lowering, often eccentrically.

Gastrocnemius (two-headed, crosses the knee) and soleus (deeper, does not cross the knee) form the calf and plantarflex the ankle. Gastrocnemius also flexes the knee.

• Heels toward the floor in Down Dog: these muscles and the calcaneal (Achilles) tendon are lengthened. Do not bounce.
• Tadasana and jumping: plantarflexors help you rise onto the balls of the feet.
• Warrior I back heel: a bent back knee changes the bias toward soleus; a straight back knee involves gastrocnemius more. That is standard two-joint muscle logic, not a Yoga Alliance-required calf sequence.

Pelvic floor at a 200-hour level means the levator ani group and coccygeus, a hammock from pubis to coccyx. Teach this much:

• It is part of a "core canister" with the diaphragm, abdominal wall, and spinal extensors.
• Gentle engagement may be cued as a lift through the perineal body, sometimes related in lineage language to mula bandha. Do not claim that gripping the pelvic floor heals incontinence, prolapse, or every low-back ache, and do not run a class as a nonstop Kegel drill.
• Breath: many quiet-breath models describe a slight yielding on inhale and recoil on exhale. A constant clench can interfere with breath and hip motion.

Pelvic pain, postpartum concerns, or prolapse symptoms: refer to a qualified pelvic-health clinician. An RYT credential does not authorize rehab protocols.

Concentric, eccentric, and isometric

Muscle tension can rise while the muscle shortens, lengthens, or stays the same length. All three are normal strength. A 200-hour teacher who only cues "engage" without naming the contraction type will not be able to explain why Chaturanga lowering shakes more than hovering.

Concentric contraction: the muscle produces force and shortens. The muscle overcomes the external load.

• Rising from Chair Pose: quadriceps shorten to extend the knees.
• Lifting into Locust: erectors and hip extensors shorten.
• Pressing from a low hover toward Plank: triceps and serratus shorten among others.

Eccentric contraction: the muscle produces force while lengthening. It controls a load you would otherwise drop.

• Lowering from Chair toward a deeper squat: quadriceps lengthen under load.
• Chaturanga lowering: elbow extensors (triceps) and scapular muscles control the descent.
• Slowly taking a back heel down in a lunge: posterior-chain control rather than a collapse.

Eccentric work is where many students feel "the shake." It is also where rushed vinyasa dumps load into wrists, knees, and lumbar joints. Cue slower descents when those joints are the concern.

Isometric contraction: force without a visible change in muscle length. The pose is a hold.

• Holding Warrior II: hip abductors and deep rotators on the front leg, plus trunk and shoulder girdle, work largely isometrically.
• Plank: serratus, abdominal wall, and quadriceps.
• Navasana: iliopsoas holding hip flexion.

Isometric does not mean "nothing is happening." It means the joint angle is being maintained. A single pose can mix types: the front quadriceps in Warrior II may be near-isometric at a fixed knee angle while you concentrically lift the arms into place.

Agonist, antagonist, synergist, stabilizer

These are roles relative to a named action, not permanent job titles. The same muscle can be agonist in one task and antagonist in the next.

• Agonist (prime mover): the main muscle producing the intended action. Hip flexion in Navasana → iliopsoas as agonist.
• Antagonist: the muscle whose action opposes the agonist. In Navasana, the hip extensors (gluteus maximus and hamstrings) are antagonists to iliopsoas. They may still provide some tension. "Antagonist" does not mean "off."
• Synergist: a helper that contributes to the same action or cancels an unwanted extra action (a neutralizer is a related idea). In knee extension, the vasti synergize with rectus femoris. In shoulder abduction, supraspinatus synergizes with deltoid.
• Stabilizer: a muscle that holds a segment relatively still, often isometrically, so the agonist can work. Rotator-cuff muscles stabilize the humeral head. Serratus anterior and lower trapezius stabilize the scapula in Plank. Deep abdominal wall and pelvic floor can stabilize the pelvis in standing balances.

Worked example: Utkatasana (Chair Pose). Gravity flexes the hips and knees as you sit. The quadriceps and gluteus maximus work eccentrically (or isometrically in a hold) to control that flexion—they are the muscles doing the work even though the joints are flexed. When you stand back up, those same muscles work concentrically as agonists of hip and knee extension. Synergists include adductors and deep hip muscles that organize the femurs, plus erectors that keep the spine from rounding. Stabilizers include ankle plantarflexors and dorsiflexors that keep you from rocking, and the abdominal wall and pelvic floor that can steady the pelvis.

Worked example: Adho Mukha Svanasana. Shoulder flexion and overhead organization recruit anterior deltoid, serratus anterior (upward rotation), and lower trapezius (depression and upward rotation). The spine is a conversation between erectors and abdominal wall, depending on whether the student dumps into lumbar extension or rounds. At the ankles, gastrocnemius and soleus are lengthened; they are not concentrically plantarflexing if the heels are reaching down. Calling every sensation in Down Dog "tight hamstrings" misses the calves, the wrists (ellipsoid joints from section 8.2), and the scapular upward rotators.

Reciprocal inhibition, kept honest. A simple 200-hour statement: when an agonist is strongly recruited, its antagonist often reduces tone. That is one reason an active quadriceps set can help some students feel a clearer hamstring lengthening. It is not a license to tell injured students that "tight muscles are just weak antagonists," and it is not treatment for a strain.

Scope of practice

• Cue actions and simple muscle names. Do not prescribe rehab for rotator-cuff tears, disc disease, or pelvic-floor disorders.
• Individual recruitment differs. Two students in "the same" Warrior II may use different synergists.
• Pain, numbness, sudden weakness, or post-surgical status: regress, stop the loaded version, and refer out.
• This chapter prepares you for school anatomy assessments and safer cueing. Independent OpenExamPrep study is not a partner publication of Yoga Alliance and does not replace your RYS 200 faculty.

If you can name gluteus maximus, hamstrings, quadriceps, iliopsoas, erectors, trapezius, serratus anterior, deltoid, the calf pair, and the pelvic floor—and you can say whether a moment is concentric, eccentric, or isometric, and which muscle is agonist versus stabilizer—you have the muscular half of the Anatomy competency this chapter is written to teach.