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“When a muscle contracts, it knows no
direction – it simply shortens.” –Lippert
Muscles are attached to bones and to
describe the relative points of attachment,
we use the terms origin and insertion.
Lippert, p39; Mansfield p37
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Muscle Origin The proximal attachment (the
point of attachment that is
closest to midline when in
anatomic position)
Typically, the more stable
point of connection (meaning
when the muscle contracts, the
origin will stay in place and
the other end where the
muscle attaches will do the
“moving”)
Biceps
Brachii
Lippert p39; Mansfield p37
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Muscle Insertion
• The distal attachment (the
point of attachment that is
farthest from midline when
in anatomic position)
• The more moveable
attachment point for the
muscle
• This attachment moves
toward the more stable
origin
Biceps
Brachii
Lippert, p39; Mansfield, p37
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Action = the joint motion that occurs as a
result of muscle shortening
Innervation = the nerve supply to the
muscle
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Agonist = a muscle or muscle group that
causes the specific movement (aka prime
mover)
Antagonist = a muscle or muscle group
that can oppose the action of the agonist
Lippert, p48
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Example: Elbow FLEXION
Agonist
• The muscle performing the task
• ______________________________
Antagonist
• The opposing muscle to the task
being performed
• _______________________________
Biceps
Brachii
Triceps
Brachii
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Example: Elbow EXTENSION
Agonist
• The muscle performing the task
• ______________________________
Antagonist
• The opposing muscle to the task
being performed
• _______________________________
Biceps
Brachii
Triceps
Brachii
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Prime Mover =
Assisting Mover = a muscle that is not
as effective as the prime mover, but does
assist in providing that same motion.
Lippert, p48
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Co-Contraction
• Agonist and Antagonist contract simultaneously
• Provide stabilization
Lippert p48; Mansfield p38
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Synergists
• Muscles that work
together
Force Couple
• Muscles that work
together in opposite
directions to
produce torque in
the same rotational
direction
Anatomic Force Couple
Mansfield p38
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Muscles have the following properties: • Irritability
• Contractility
• Extensibility
• Elasticity
To better understand these properties,
you need to know that muscles have a
normal resting length
Normal resting length = the length of a
muscle when there are no forces or
stresses placed upon it. Lippert, p42
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Irritability
• The ability to respond to a stimulus
A muscle contracts when stimulated.
Lippert p42
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Contractility
• The ability to contract,
producing tension between
the origin and insertion of
the muscle.
Muscle may:
Stay the same length
(isometric)
Shorten
(concentric)
Lengthen
(eccentric) Lippert p42
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Contractility continued
An active muscle develops force in only
one of the following 3 ways:
How Type
By shortening Concentric
By resisting elongation Eccentric
By remaining at a
constant length
Isometric
Lippert, p42
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Contractility continued
CONCENTRIC Contraction
• The distance between the origin and
insertion is decreasing
• The internal torque produced by the
muscle is greater than the external
torque produced by an outside force.
Lippert, p45
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Contractility continued
ECCENTRIC Contraction
• The origin and insertion become farther apart.
• The muscle is attempting to contract, but is
simultaneously pulled to a longer length by a
more dominant external force.
• The external torque, often generated by gravity,
exceeds the internal torque produced by muscle.
• Most often, gravity or a held weight is allowed
to “win,” effectively lengthening the
muscle in a controlled manner.
Lippert, p45
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Contractility continued
ISOMETRIC Contraction
• The muscles remains the same length
• The origin and insertion remain the same
distance to each other
• The muscle generates an internal torque
equal to the external torque
• There is no motion or change in joint
angle
Lippert, p45
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Extensibility
• The ability to stretch (or lengthen)
when a force is applied.
Lippert p42
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Elasticity
• The ability to recoil, or return to a
normal resting length once the stimulus
or force to stretch or shorten has been
removed.
Lippert p42
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Stretch a muscle and it will lengthen.
• extensibility
Lippert p42
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Remove the stretch, and it will return to its normal
resting position.
• elasticity
Lippert p42
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Stimulate a muscle and it will respond,
• irritability
by contracting
• contractility
Lippert p42
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Then remove the stimulus and it will return to its
normal resting position.
• elasticity
Lippert p42
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Location
Shape
Action
Number of heads
Attachments
Direction of the fibers
Size of the muscle
Lippert, p40
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Location
Shape
Action
Number of heads
Attachments
Direction of the fibers
Size of the muscle
Lippert, p40
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Location
Shape
Action
Number of heads
Attachments
Direction of the fibers
Size of the muscle
Extensor Indicis
Lippert, p40
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Location
Shape
Action
Number of heads • Biceps Brachii
• Triceps Brachii
Attachments
Direction of the fibers
Size of the muscle
Lippert, p40
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Location
Shape
Action
Number of heads
Attachments • Sternocleidomastoid
Direction of the fibers
Size of the muscle
Lippert, p40
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Location
Shape
Action
Number of heads
Attachments
Direction of the fibers • Vastus Medialis Oblicus
(VMO)
Size of the muscle
Lippert, p40
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Location
Shape
Action
Number of heads
Attachments
Direction of the fibers
Size of the muscle • Pectoralis Major
Lippert, p40
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The Sarcomere = The basic contractile
unit of muscle • It is composed of two main protein filaments
Actin
Myosin
http://www.youtube.com/watch?v=0kFmbrRJq4w
Mansfield, p38
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Sliding Filament Theory: the most
popular model that describes muscular
contraction
The thick myosin filament contains
numerous heads which attach to the
thinner actin filaments and create actin-
myosin bridges.
Mansfield, p38
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Muscle Fiber Arrangement • Muscle fibers are arranged either parallel or
oblique to the muscle’s long axis.
• The fiber arrangement and shape are important
indicators of a muscle’s specific action
Lippert p41; Mansfield p40
Parallel Oblique
Strap Unipennate
Fusiform Bipennate
Rhomboidal Multipennate
Triangular
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Fiber Arrangement
Parallel
• Tend to be longer
• Have a greater range of
motion
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Fiber Arrangement
Oblique
• Shorter
• More numerous (Dense)
Great strength
Lippert, p41
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Fiber Arrangement
Parallel • Strap Muscles
• Long and thin with fibers
running the entire length
of the muscle
• Examples: sartorius,
rectus abdominis, SCM
Lippert, p41
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Fiber Arrangement
Parallel • Fusiform Muscles
• Wider in the middle and
tapers at both ends
• Most fibers run the entire
length of the muscle
• Examples: brachioradialis,
biceps, brachialis
Lippert, p41
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Fiber Arrangement: Parallel • Rhomboid muscle
Four sided
Usually flat
Broad attachments at each end
Pronator teres
Gluteus maximus
Rhomboids in the shoulder girdle
Lippert, p41
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Fiber Arrangement:
Parallel
Triangular Muscle
• Narrow attachment on
one end (insertion)
• Broad attachment on the
other end (origin)
Pectoralis major
Lippert, p41
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Fiber Arrangement: Oblique
Unipennate • Fibers arranged in a pattern that resembles one
side of a feather
Short fibers attaching diagonally into a central tendon
Tibialis posterior
Lippert, p41
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Fiber Arrangement: Oblique
Bipennate • Short fibers that bilaterally attach into a central
tendon
• Featherlike in appearance
Rectus femoris
Rectus abdominus
Lippert, p41
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Fiber Arrangement:
Oblique
Multipennate
• Muscles have many
tendons with oblique
muscle fibers in
between them
Deltoid
Subscapularis
Lippert, p41
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Line of Pull
The direction of a muscle’s force is
referred to as its line of pull.
This determines its action • If a muscle crosses a joint, it acts on that joint
Mansfield, p41
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“There is an optimum range of a muscle
within which it contracts most
effectively.” Lippert, p42
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Active Length-
Tension
Relationship
• Strength of the muscle
is the least when the
muscle is in its
shortest position and
also when it is in its
longest position
• Strength is greatest at
mid-length
Mansfield, p42-43
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Active Insufficiency
• The point at which a muscle cannot shorten any
father because the tension within the muscle
becomes insufficient at both extremes.
• It occurs to the agonist (the muscle that is
contracting).
• Example: hamstring
Lippert, p43 &
Mansfield, p45
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Passive Insufficiency
• Occurs when a muscle cannot be elongated any
farther without damage to its fibers.
• It occurs to the antagonist (the muscle that is
relaxed and on the opposite side of the joint
from the agonist)
• Example: hamstring
Lippert, p43 &
Mansfield, p45
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Tenodesis (based upon passive insufficiency)
• while resting the elbow on a table, flexing the wrist
will have a tendency to extend the fingers
Lippert, p44
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Tenodesis (due to passive insufficiency) Supinating the forearm and extending the wrist will
have a tendency to flex the fingers
*This can help someone either grasp something or release something…
Lippert, p44
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Speed Matters: • Concentric activation
Muscle produces less force as the speed of the
muscle contraction increases
You can repeatedly lift lighter versus heavy objects at great
speed
The muscle cannot produce force at great speeds when the
objects are heavy
Mansfield, p44
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Speed Matters: • Isometric activation creates greater force than
any speed concentric contraction
• Eccentric activation
Force production increases slightly as the speed of the
elongation increases
Mansfield, p44
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Closed Chain
• The distal segment is
fixed (closed)
• The proximal segment
moves
• Lower Extremity
example:
• Upper Extremity
Example:
Open Chain
• The proximal segment
is fixed (remains
stationary)
• The distal segment is
free to move
• Lower Extremity
Example:
• Upper Extremity
Example:
Lippert, p49-50
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Due to the adaptability of muscular tissue: • Muscle will assume the length most common to it
A muscle held in a shortened position over time will
______________________________
A muscle held in an elongated position over time will
__________________________
Mansfield, p46
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Immobility can cause muscle tightness and/or loss of
motion
Severe loss of motion can lead to joint contracture
The joint is incapable of permitting full motion
Mansfield, p46
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A muscle held in an elongated position
over time will _________________
Which muscles are elongated?
How does that affect muscle activation?
Mansfield, p46
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A protective mechanism:
• This is referred to as
muscle guarding
• The muscular system
“tightens” to help protect the
body from further injury
however;
Circulation is impaired
Metabolites build up
Pain results
Edema results
Lippert, p32
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Muscle Action Stretch Position
Gastrocnemius
Hamstring
Quad
Abdominals
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As a general principle,
optimal stretching of a muscle
requires the therapist to hold
a limb in a position that is
______________ to all of the
muscle’s actions.
Mansfield, p47
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Mono-articular muscles
Bi-articular muscles
What does this mean and how do we
stretch them?
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Muscle Action How to Strengthen it
Concentrically
Gastrocnemius
Hamstring
Quad
Abdominals
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As a general principle,
concentric strengthening of a
muscle requires the patient to
move a joint in the direction
that is ______________ as the
muscle’s actions.
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http://www.youtube.com/watch?v=uO_C
NYidOw0
http://www.youtube.com/watch?v=GWvJ
14cwwKU
http://www.youtube.com/watch?v=9jvJvP
rayXU
http://www.youtube.com/watch?v=Gypw
mdhMVcc
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Lippert, L.S. (2011). Clinical Kinesiology
and Anatomy, 5th ed. Philadelphia, PA: F.A.
Davis.
Mansfield, P.J., & Neumann, D.A. (2009).
Essentials of Kinesiology for the Physical
Therapist Assistant. St. Louis, MO: Mosby
Elsevier.