Lesson 13 of 14 · Yoga & anatomy

Muscles, contraction & movement

Understand the work beneath the shape.

Three muscle tissues, contraction types, muscle roles and the neck, back, hip, hamstring and calf names in the notebook.

Notes: Daniel Fewtrell · Edited 17 September 2026
Educational study material · No named teacher review recorded

01 · Study

Three muscle tissues

The notebook’s “600 muscles” is an approximate conventional count of skeletal muscles, not a total of all muscle cells. Muscle activity supports movement, posture, joint stability and heat production. Breathing is not performed exclusively by smooth muscle: the diaphragm is skeletal muscle.

Tissue	Typical location	Control
Skeletal	Most muscles moving the skeleton; also the diaphragm	Voluntary actions, with reflex and automatic contributions.
Cardiac	Heart wall	Involuntary rhythmic activity.
Smooth	Walls of hollow organs and blood vessels	Largely involuntary.

Labeled anterior and posterior views of the human body showing major superficial muscles and selected deeper muscles. — **Muscular system: front and back**Muscular system: front and back — OpenStax, CC BY 4.0 (via Wikimedia Commons). Source · CC BY 4.0Select the image for a full-size view.

Further reading: OpenStax · Muscle tissues ↗

02 · Study

Properties are not training goals

Extensibility does not mean a muscle should be pushed as far as possible. A sensation of tightness alone cannot establish which tissue is limiting movement.

Term	Meaning
Excitability	Responding to a stimulus; “irritability” is an older physiological synonym, not an emotion.
Contractility	Generating force.
Extensibility	Being lengthened within a physiological range.
Elasticity	Recoil towards an earlier length.
Adaptability	A broader response to repeated demands, rather than a separate basic tissue property in every textbook.

Further reading: OpenStax · Muscle tissues ↗ · NCCIH · Yoga effectiveness and safety ↗

03 · Study

A contraction does not always shorten a muscle

Isometric does not mean “strength” while isotonic means “flexibility”: both can involve substantial effort. A pose combines different actions across muscles. Keep breathing rather than treating a hold as a breath-holding exercise.

Action	What changes	Study example
Concentric	Active muscle shortens	Elbow flexors lifting a light object.
Eccentric	Active muscle lengthens while controlling a load	The same flexors lowering it slowly.
Isometric	Force with little change in overall muscle length or joint angle	Holding the object still.
Isotonic	Length changes against a broadly steady load; an idealised term	Often used to group concentric and eccentric actions.
Isokinetic	Movement at a controlled constant angular speed	Usually studied using specialised equipment.

Further reading: OpenStax · Control of muscle tension ↗

04 · Study

Agonist, antagonist and synergist

These are changing roles, not permanent labels on a muscle. The antagonist is not simply switched off: muscles may co-contract to control a joint. The notebook’s “atrophy” means loss of muscle size; it cannot be identified from feeling stiff or tired.

Role	In a particular action
Agonist	A main contributor to the intended movement.
Antagonist	Can oppose or help control that movement.
Synergist	Assists or stabilises so the action can occur.

Whole-body anatomy atlas ↗

05 · Study

Neck, shoulder blade and back

Torticollis is a clinical term for an abnormal neck posture with several possible causes, not a synonym for ordinary stiffness. Do not force the head into position from the notebook’s “wry neck” annotation.

Name	Location and action	Notebook clarification
Sternocleidomastoid	Front/side of neck; contributes to turning and bending the head	Not a diagnosis of every stiff neck.
Levator scapulae	Neck to upper inner shoulder blade; helps elevate the scapula	Neck side-bending depends on what is fixed.
Trapezius	Broad superficial upper-back muscle; portions move and stabilise the scapula differently	The two sides form the familiar broad outline.
Rhomboid major and minor	Deep to trapezius; retract and stabilise the shoulder blade	C7–T5 is a combined regional shorthand, not one attachment for both muscles.
Latissimus dorsi	Broad back muscle acting on the upper arm	Helps extend, adduct and internally rotate the humerus.

Labeled posterior and lateral views of superficial and deep neck muscles, including sternocleidomastoid, trapezius and splenius capitis. — **Muscles of the neck**Muscles of the neck — OpenStax, CC BY 4.0 (via Wikimedia Commons). Source · CC BY 4.0Select the image for a full-size view.

Labeled views of muscles along the neck and vertebral column, including the erector spinae group and deeper spinal muscles. — **Muscles of the neck and back**Muscles of the neck and back — OpenStax, CC BY 4.0 (via Wikimedia Commons). Source · CC BY 4.0Select the image for a full-size view.

Further reading: OpenStax · Head, neck and back ↗ · OpenStax · Shoulder girdle and upper limb ↗

06 · Study

Hips, hamstrings and calves

Gluteus maximus is not a fourth hamstring. “Plantar flexion” means pointing the foot away from the shin, not folding the trunk. Muscles that cooperate in a movement need not belong to the same anatomical group.

Group	Main study points
Iliopsoas	Iliacus and psoas major work together in hip flexion.
Gluteus maximus	A major hip extensor.
Gluteus medius and minimus	Contribute to hip abduction and pelvic control.
Hamstrings	Biceps femoris, semitendinosus and semimembranosus; bend the knee, with most portions also extending the hip.
Gastrocnemius and soleus	The major calf muscles; both plantar-flex the ankle. Gastrocnemius also crosses the knee.

Labeled anterior and posterior views of the hip and thigh, showing gluteal muscles, quadriceps, hamstrings, adductors and other muscles acting on the hip and knee. — **Hip and thigh muscles**Hip and thigh muscles — OpenStax, Anatomy and Physiology, CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction Source · CC BY 4.0Select the image for a full-size view.

Labeled anterior and posterior views of lower-leg muscles, with superficial and deep posterior muscles including gastrocnemius, soleus and tibialis posterior. — **Muscles of the lower leg**Muscles of the lower leg — OpenStax, Anatomy and Physiology, CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction Source · CC BY 4.0Select the image for a full-size view.

Further reading: OpenStax · Pelvic girdle and lower limb ↗

07 · Study

Use the map without self-diagnosing

The class ends with “strengthening and stretch”. These are complementary possibilities, not an instruction to stretch every painful area. Range, load, recovery and control all matter; an illustrated muscle cannot tell you the cause of a symptom.

Symptom and stretch finder ↗Joints and movement ↗

Further reading: NCCIH · Yoga effectiveness and safety ↗

From notebook to page

IMG_1859–1860, IMG_1866 and IMG_1868–1869. Spellings are standardised; incomplete attachment labels and clinical shorthand are qualified rather than turned into diagnoses.

Spelling has been standardised and explanations added. Traditional teaching cues, anatomical facts and uncertain handwriting are distinguished in the text. These pages support learning alongside appropriate teaching.