18
HUMAN ANATOMY
There are about 640 muscles in your
body. Your skeletal muscles are attached
to your bones, allowing you to move.
Some muscles are supercial (close to
the surface) and others are deep.
SYSTEM OVERVIEW
As you study each of these key chosen
muscles, try to palpate or physically touch
them while visualizing their internal
location. This will help you learn better,
while improving your mind-body
connection. Most of the muscles
here are categorized into groups
based on their actions.
MUSCULAR
SYSTEM
Pectorals
Pectoralis major
Pectoralis minor
Elbow exors
Biceps brachii
Brachialis (deep)
Brachioradialis
Intercostal muscles
Abdominals
Rectus abdominis
External abdominal
obliques
Internal abdominal
obliques
(deep, not shown)
Transversus abdominis
Ankle dorsiexors
Tibialis anterior
Extensor digitorum longus
Extensor hallucis longus
Brachialis
Hip exors
Iliopsoas (iliacus
and psoas major)
Rectus femoris
(see quadriceps)
Sartorius
Adductors
(see below)
Adductors
Adductor longus
Adductor brevis
Adductor magnus
Pectineus
Gracilis
Quadriceps
Rectus femoris
Vastus medialis
Vastus lateralis
Vastus intermedius
(deep, not shown)
Skeletal muscle
There are three types of muscle tissue:
cardiac, smooth, and skeletal. We will focus
on skeletal muscle as it is responsible for the
movement of joints in asana. This is what it
looks like under a microscope.
Striations are visible
stripes from internal
structures (see p.21)
Muscle fibers are
arranged in
parallel orientation
DEEP
SUPERFICIAL
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19
Trapezius
Rhomboids
Rhomboid minor
Rhomboid major
Cervical extensors
Splenius capitis
Splenius cervicis
Gluteus medius
Hip extensors
Gluteals
Adductor magnus
Hamstrings
Biceps femoris
Semitendinosus
Semimembranosus
Deltoids
Spinal extensors
Cervical extensors (above)
Erector spinae
Transversospinales
(small, deep muscles
along spine)
Gluteals
Gluteus maximus
Gluteus medius
Gluteus minimus
Latissimus dorsi
Triceps brachii
Piriformis
Hip exors
Iliopsoas (iliacus
and psoas major)
Rectus femoris
(see quadriceps)
Sartorius
Adductors
(see below)
Muscle has more
blood flow and
stretching capacity
DEEP
SUPERFICIAL
Levator scapulae
Serratus posterior
Ankle plantar exors
Tibialis posterior
Calf muscles
Gastrocnemius
Soleus
Adductor
magnus
Tendons
Tendons are tough cords of dense
connective tissue attaching muscle to bone.
As bundles of parallel collagen bers, they
have little elasticity or blood ow. In general,
you want to stretch muscles, not tendons.
Collagen fibers resist
pull or tension
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Fascicle
A bundle of
muscle cells
Muscle cell
Also called a
muscle fiber
Myobril
Microscopic
contractile
proteins
M line
Middle of a
sarcomere
PLANTAR
FASCIA
TYPES OF CONTRACTION
Isotonic contractions involve a change in muscle length,
as in the act of flexing or extending your elbow (see
below) or transitioning in or out of an asana. Isometric
contractions involve tension with no change in muscle
length, such as when holding an asana.
ECCENTRIC CONTRACTION
Eccentric contractions occur when muscle fibers
“lengthen” to change the angle of a joint. This
occurs in your biceps when extending your elbow
as you lower a weight, or in your hamstrings when
extending your knee as you transition from
Warrior II to Triangle (see pp.118–21) pose.
MUSCLE STRUCTURE
Skeletal muscles are bundles of bundles of bundles
of parallel muscle cells, blood vessels, and nerves
wrapped with connective tissue, including fascia.
Fascia creates a network through and around muscles
and other structures of your body. Microscopic
proteins in your muscles cause muscle contractions.
HOW MUSCLES WORK
Muscles often work in antagonistic pairs. As the
agonist muscle engages, the antagonist generally
releases. Synergist muscles engage around the joint
to support the action.
Z disk
Edge of a
sarcomere
Thin lament
Made of the
protein actin
Thick lament
Made of the
protein myosin
Fascia
Fascia is similar to the white
pith of an orange; it separates
parts yet integrates the whole.
Fascia is not just found
around muscles. It is also
around vital organs and
woven throughout your body.
This body-wide network of
fascia is part of the reason
why a yoga pose that aects
your foot can suddenly
release your tight shoulders.
Fascia
connects heel
to toes
Flat band of
connective
tissue
Extension
Angle of joint increases
Antagonist
Biceps brachii is the
antagonist as it
mostly relaxes
Agonist
Triceps brachii is the agonist
as it concentrically contracts
to extend the elbow
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Flexion
Angle of joint
decreases
Agonist
Biceps brachii is the
agonist as it concentrically
contracts to flex the elbow
CONCENTRIC CONTRACTION
Concentric contractions occur when the muscle fibers
“shorten” to change the angle of a joint. This occurs in
your biceps when flexing your elbow as you lift a weight,
or in your hamstrings when flexing your knee as you
move into Warrior II (see pp.102–05).
CONTRACTED SARCOMERE
RELAXED SARCOMERE
Muscle contraction
A cascade of events initiated
by a signal from the nervous
system and the presence of
calcium leads to the removal
of the blockage on actin of
the thin lament, allowing
the thick and thin lament to
connect. The thick lament
pulls the thin lament in
toward the M-line, bringing
the Z-disks closer together.
COLLAGEN FIBERS
Thick
filament
Thin filament
M line
Z disk
Antagonist
Triceps brachii is the
antagonist as it
mostly relaxes
HUMAN ANATOMY Muscular System
Movement and fascia
Research suggests that the
collagen bers of the fascia
surrounding healthy muscles
are organized in a crisscross,
lattice structure. Inactivity and
aging seem to cause your
fascia to lose its structural
integrity. Asana may help
organize your fascia, helping
you move and feel better.
Healthy double
lattice collagen
orientation
Random collagen
orientation from
inactivity
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