Download muscle lecture

Muscle
• internal motors of human body
responsible for all movements
of skeletal system
• only have the ability to pull
• must cross a joint to create
motion
• can shorten up to 70% of
resting length
Muscle-Tendon Model
• 3 components
CC
contractile component
SEC
series elastic
component
PEC
parallel elastic component
Muscle Model
Whole
Muscle
•Contractile Component (CC)
CC
SEC
PEC
–active shortening of muscle through
actin-myosin structures
•Parallel Elastic Component (PEC)
–parallel to the contractile element of
the muscle
–the connective tissue network
residing in the perimysium,
epimysium and other connective
tissues which surround the muscle
fibers
•Series Elastic Component (SEC)
–in series with the contractile
component
–resides in the cross-bridges between
the actin and myosin filaments and the
tendons
Tissue
Viscoelastic Structures
CC
SEC
PEC
Both SEC & PEC behave like
springs when acting quickly but
they also have viscous nature
If muscle is statically stretched it
will progressively stretch over
time and will slowly return to
resting length when the
stretching force is removed.
Whole
Muscle
Stretch-Shortening Cycle
• a quick stretch followed by
concentric action in the muscle
• Store energy in elastic structures
• Recover energy during concentric
phase to produce more force than
concentric muscle action alone
• examples
– vertical jump: counter-movement
vs. no counter-movement
– plyometrics
CC
SEC
PEC
Tissue
Tissue Properties of Muscle
• irritability - responds to stimulation by a
chemical neurotransmitter (ACh)
• contractibility - ability to shorten (50-70%),
usually limited by joint range of motion
• distensiblity - ability to stretch or lengthen,
corresponds to stretching of the perimysium,
epimysium and fascia
• elasticity - ability to return to normal state
(after lengthening)
Tissue
Muscle Structure
“Bundle-within-a-Bundle”
Tissue
Sliding Filament Theory
1) Myosin filaments form a
cross-bridge to actin
2) Myosin pulls actin
actin
myosin
3) x-bridge releases
4) Myosin ready for another
x-bridge formation
Motor Neurons
Dendrite
receives and
integrates
information
Soma
(body)
Axon
transmits information
Motor Unit
A motor unit
is composed
of a motor
neuron and
all of the
muscle fibers
it innervates
It is the smallest functional unit of muscular shortening
Motor Unit
(cont)
• each muscle has many motor units (m.u.)
• # of fibers in a m.u. is dependent on the
precision of movement required of that
muscle (average: 100-200 fibers per m.u.)
– more precision is obtained with more neurons
– 100 to 2000 motor neurons per muscle
• # of m.u.’s in a muscle decreases in the
elderly
Precision of 2 Muscles
1st muscle
2nd muscle
10,000 fibers
100 motor neurons
10,000 fibers
200 motor neurons
100 motor units
100 fibers/mu
200 motor units
50 fibers/mu
less precision
more precision
Muscle
Number of
Muscle
Fibers
Number of
MU’s
Mean
Number of
Fibers Per
MU
27,100
1,100
25
Brachioradialias >129,200
330
>410
First Lumbrical
10,000
100
110
Tibialias
Anterior
250,000
450
600
Gastrocnemius
(medial head)
1,120,000
580
2,000
Platysma
Neuromuscular Control
• a motor nerve action potential stimulates the
release of acetylcholine (ACh) from the nerve
ending
Monitor this action
potential using
Electromyography
• ACh binds to the muscle fiber which causes
depolarization and results in the release of calcium
ions from the sarcoplasmic reticulum (5 ms)
• the calcium ions permit the actin-myosin
interaction, which produces force
• the contraction stops when the calcium ions are
removed by a pumping action (100 ms)
Control of Tension
• excitation of each motor unit is an all-ornothing event
• increased tension can be accomplished by:
– increasing the # of stimulated motor units
(recruitment)
– increasing the stimulation rate of the active
motor units (rate coding)
Stimulation vs Activation
Voltage
Voltage
threshold
NOTHING
ALL
Recruitment
• each motor unit has a stimulation threshold
at which it will begin to produce force
• small motor units have a lower threshold
than large motor unit, therefore they are
recruited first (size principle)
Rate Coding
summation (B) - the
overall effect of added
stimuli
tetanus (C) - sustained maximal
tension due to high frequency
stimulation
Tissue
Fiber Types
• all fibers within a motor unit are of the same
type
• within a muscle there is a mixture of fiber
types
• fiber type may change with training
• recruitment is ordered
– type I recruited 1st (lowest threshold)
– type IIa recruited second
– type IIb recruited last (highest threshold)
Tissue
Tissue
Fiber Type Comparison
Shortening
Speed
Energy System
Size
Force
Production
Aerobic
Capacity
Anaerobic
Capacity
Fatigability
Type I
slow
Type IIa
fast
Type IIb
fast
oxidative
glycolytic
small
low
oxidative,
glycolytic
large
high
high
medium
low
low
medium
high
low
medium
high
large
high
Fiber Types
Muscle
Fiber Type
(%SO, %FOG, %FG)
vastus medialis
50, 15, 35
erector spinae
58, - ,42
soleus
80, - , 20
orbicularis oculi
15, - , 85
From: Multiple Muscle Systems, Winters and Woo
Sarcomere Organization
Tissue
• the number of sarcomeres in series or in
parallel will help determine the properties
of a muscle
3 sarcomeres in series
3 sarcomeres in parallel
(high velocity/ROM orientation)
(high force orientation)
Sarcomere organization example:
Note that the values are not representative of actual
sarcomeres.
1
3 sarcomeres 3 sarcomeres
sarcomere
in series
in parallel
Force
1N
1N
3N
ROM
1 cm
3 cm
1 cm
Time
1 sec
1 sec
1 sec
Velocity
1 cm/sec
3 cm/sec
1 cm/sec
Sarcomere Organization
• the longer the tendon-to-tendon length the
greater number of sarcomeres in series
• the greater the physiological cross-sectional
area (PCSA) the greater number of
sarcomeres in parallel
sarcomeres in series
sarcomeres in parallel
Muscle Structure
Fusiform (parallel)
• fibers run
longitudinally
• generally fibers do
not extend the entire
length of muscle
Tissue
Muscle Structure
Pennate
• tendon runs
parallel to the
long axis of the
muscle, fibers
run diagonally to
axis (short
fibers)
Pennation Angles
Muscle
gastrocnemius
Pennation Angle
(deg)
10-25
soleus
15-30
tibialis anterior
5-10
biceps femoris
0
From: Multiple Muscle Systems, Winters and Woo
Fusiform vs. Pennate
• fusiform
– advantage: sarcomeres are in series
so maximal velocity and ROM are
increased
– disadvantage: relatively low # of
parallel sarcomeres so the force
capability is low
• pennate
– advantage: increase # of sarcomeres
in parallel, so increased PCSA and
increased force capability
– disadvantage: decreased ROM and
velocity of shortening
Tissue
Muscle Attachment - Tendons
Fusion b/w
epimysium
and periosteum
Tendon fused
with fascia
Whole
Muscle
Muscle Terms
Whole
Muscle
attachment can be directly to the bone or indirectly
via a tendon or aponeurosis
Origin -- generally proximal, fleshy attachment to the stationary bone
Insertion -- generally distal, tendinous and attached to mobile bone
defining origin or insertion
relative to action of bone is
difficult
e.g. hip flexors in leg raise v.
sit-up
Functions of Muscle
Whole
Muscle
• produce movement - when the muscle is
stimulated it shortens and results in movement of
the bones
• maintain postures and positions - prevents
motion when posture needs to be maintained
• stabilize joints - muscles crossing a joint can pull
the bones toward each other and contribute to the
stability of the joint
Functional Muscle
• generally have more than
1 muscle causing same
motion at a joint
• together these muscles are
referred to as a functional
group
• e.g. elbow flexors -biceps brachii, brachialis,
and brachioradialis - all
flex elbow
Whole
Groups Muscle
Role of the Muscle
Whole
Muscle
• prime mover - the muscles primarily responsible
for the movement
• assistant mover - muscles used only when more
force is required
• agonist - muscles responsible for the movement
• antagonist - performs movement opposite of
agonist
• stabilizer - active in one segment to stabilize a
bone so that a movement in an adjacent segment
can occur
• neutralizer - active to eliminate an undesired joint
action of another muscle
Whole
Muscle
SHOULDER ABDUCTION
agonist: deltoid
antagonist: latissimus dorsi
stabilizer: trapezius
holds the shoulder girdle in place so
the deltoid can pull the humerus up
neutralizer: teres minor
if latissimus dorsi is active then the
shoulder will tend to internally
rotate, so the teres minor can be
used to counteract this via its ability
to externally rotate the shoulder
Muscular Action
• isometric action
– no change in fiber
length
• concentric action
– shortening of fibers to
cause movement at a jt
• eccentric action
– lengthening of fibers to
control or resist a
movement
Whole
Muscle
Whole
Muscle
Whole
Muscle
Concentric action:
• work against gravity to raise the
body or objects
• speed up body segments or objects
Eccentric action:
• work with gravity to lower the body or objects
• slow down body segments or objects
concentric
eccentric
Elbow Actions
•push-up
up - concentric action of elbow extensors
down - eccentric action of elbow extensors
•catching a baseball
eccentric action of elbow extensors
•throwing a baseball
concentric action of elbow extensors
•pull-up
up - concentric action of elbow flexors
down - eccentric action of elbow flexors
Whole
Muscle
Whole
Muscle
The countermovement elicits
an increase in force production
the increase in force production
is 30% neural and 70% elastic
contribution
Greatest return of energy is
achieved using a “dropstop-pop” action with only
an 8”-12” drop
Whole
Muscle
Number of Joints Crossed
• uniarticular or monoarticular - the
muscle crosses 1 joint, so it affects motion
at only 1 joint
• biarticular or multiarticular - the muscle
crosses 2 (bi) or more (multi) joints, so it
can produce motion across multiple joints
Multiarticular Muscles
• can reduce the
contraction velocity
• can transfer energy
between segments
• can reduce the
work required of
single-joint muscles
• more susceptible to
injury
Whole
Muscle
Insufficiency
Whole
Muscle
• a disadvantage of 2-joint muscles
– active insufficiency - cannot actively shorten to
produce full ROM at both joints simultaneously
– passive insufficiency - cannot be stretched to
allow full ROM at both joints simultaneously
Insufficiency Example
Whole
Muscle
• squeeze the index finger of another student
• move the wrist from extreme
hyperextension to full flexion
• What happens to the grip strength
throughout the ROM?
• WHY?
Active Length-Tension
l0 - neither contracted
nor stretched
T
e
n
s
i
o
n
Length
l0
Tissue
Tissue
Length-Tension
l0 - neither contracted
nor stretched
physiological
limit
combined
T
active
passive
l0
L
Tissue
Force - Velocity
Relationship
force
v<0
(eccentric)
v=0
(isometric)
v>0
(concentric)
velocity of contraction
Tissue
Power - Velocity
Relationship
F
Power (F*v)
v
30% vmax
Electromechanical Delay
• electromechanical delay - stimulation
begins before force is developed
– it is thought that this is the time necessary to “take up
the slack in the SEC”
Whole
Muscle
Movement/Activity Properties of
Muscle
• flexibility - the state of muscle’s length
which restricts or allows freedom of
joint movement
• endurance - the ability of muscles to
exert force repeatedly or constantly
Whole
Muscle
Movement/Activity Properties of
Muscle (cont.)
• strength - the maximum force that can
be achieved by muscular tension
• power - the rate at which physical
work is done or the force created by a
muscle multiplied by its contraction
velocity
Muscular Strength
Whole
Muscle
• measure absolute force in a single muscle
preparation
• in real life most common estimate of muscle
strength is maximum torque generated by a
given muscle group
Strength Gains
Training focuses on developing
larger x-sectional area
AND developing more tension
per unit of x-sectional
area
from an “untrained state”
1st 12 weeks see improvement on
the neural side via improved
innervation
later see increase in x-sectional
area
Whole
Muscle
Magnitude of strength
gains
dependent on
1) genetic predisposition
2) training specificity
3) intensity
4) rest
5) volume
Whole
Muscle
Isotonic
Exercise
Isokinetic
Exercise
Isometric
Exercise
Training Modalities
Close-Linked
Exercises
Variable Resistance
Exercise
Whole
Muscle
Muscle Injury
Greatest Risk
a) 2-joint muscles
b) muscles that limit ROM
c) muscles used eccentrically
Individuals at risk
a) fatigued state
b) not warmed-up
c) new exercise/task
d) compensation
Soreness v. Damage
damage believed to be in fiber
soreness due to connective tissue
Muscular Force Components
• rotary component
– causes motion
– perpendicular to the
rotating segment
Whole
Muscle
• stabilizing or dislocating
component
– parallel to rotating segment
– stabilizing is toward joint
– dislocating is away from joint
Muscular Force Components
Whole
Muscle
• components depend on the joint angle
large rotary
small stabilizing
small rotary
large stabilizing
medium rotary
medium dislocating
What Causes Motion?
Force or Torque?
• angular motion occurs at a
joint so technically torque
causes motion
• torque is developed
because the point of
application of the force
produced by muscle is
some distance away from
the joint’s axis of rotation
Whole
Muscle
muscle force (Fm)
muscle torque (Tm)
distance between pt of
application and joint axis
(dm)
Whole
Muscle
Calculation of Muscle Torque
400 N
o
60
0.03 m
*
Tm = Fm
d
Torque = 400 N * 0.03 m
becasue Fm is not perpendicular
to the forearm!!!
Fm
Fm
Fm
To solve problem we must
resolve the vector Fm into
components which are
perpendicular (Fm ) and
parallel (Fm ) to the forearm.
Whole
Muscle
Calculation of Muscle Torque
Fm
Fm
400 N
Fm
Fm
Fm
Fm
0.03 m
Only the perpendicular component will create a torque
about the elbow joint so only need to calculate this.
Whole
Muscle
T = 345 N * 0.03 m = 10.4 Nm
400 N
FR = 345 N
Angle of Pull Affects Torque
0.03 m
400 N
T = 200 N * 0.03 m = 6 Nm
0.03 m
FR = 200 N
Whole
Muscle
T = 345 N * 0.03 m = 10.4 Nm
400 N
0.03 m
FR = 345 N
Size of Muscle Force Affects Torque
FR = 345 N
600 N
FR = 520 N
T = 520 N * 0.03 m = 15.6 Nm
0.03 m
Whole
Muscle
T = 345 N * 0.03 m = 10.4 Nm
400 N
FR = 345 N
0.03 m
Moment Arm Affects Torque
400 N
T = 345 N * 0.1 m = 34.5 Nm
FR = 345 N
0.1 m
Whole
Muscle
Calculation of Muscle Torque
Fm
Fm
400 N
Fm
Fm
o
60
Fm
Fm
o
60
0.03 m
NOTE: The torque created by the muscle depends on
1) the size of the muscle force
2) the angle at which the muscle pulls
3) the distance that the muscle attaches away from joint axis
Factors Affecting Torque
Whole
Muscle
Changing any of these 3 factors will change the torque:
1) muscle force - changed by increased neural stimulation
2) d - can’t change voluntarily but use of other muscles in
same functional muscle group gives a different d
3) q - this changes throughout the ROM
Whole
Muscle
Additional Factors Affecting Torque
Muscle Force
1) level of stimulation
2) muscle fiber type
3) PCSA
4) velocity of shortening
5) muscle length
Angle of pull
Moment arm