internal motors of human body responsible for all movements of skeletal system

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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

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Muscle-Tendon Model

• 3 components

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Muscle Model
Whole Muscle

• Contractile Component (CC)
• 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

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Tissue
Viscoelastic Structures
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.
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Stretch-Shortening Cycle
Whole Muscle

• 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

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Tissue Properties of Muscle
Tissue

• 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)

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Muscle Structure
Tissue
Bundle-within-a-Bundle
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Tissue
Sliding Filament Theory
1) Myosin filaments form a cross-bridge to
actin
2) Myosin pulls actin
4) Myosin ready for another x-bridge formation
3) x-bridge releases
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Sarcomere Organization
Tissue

• the number of sarcomeres in series or in parallel
  will help determine the properties of a muscle

3 sarcomeres in series (high velocity/ROM
orientation)
3 sarcomeres in parallel (high force orientation)
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Sarcomere organization example Note that the
values are not representative of actual
sarcomeres.
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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
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Muscle Structure Fusiform (parallel)

• fibers run longitudinally
• generally fibers do not extend the entire length
  of muscle

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Muscle StructurePennate
Tissue

• tendon runs parallel to the long axis of the
  muscle, fibers run diagonally to axis (short
  fibers)

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Fusiform vs. Pennate
Tissue

• 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

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Fiber Types
Tissue

• 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)

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Tissue
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Fiber Type Comparison
Tissue
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Active Length-Tension
Tissue
- neither contracted nor stretched
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Length-Tension
Tissue
- neither contracted nor stretched
T
L
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Tissue
Force - Velocity Relationship
v lt 0 (eccentric)
v gt 0 (concentric)
force
velocity of contraction
v0 (isometric)
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Tissue
Power - Velocity Relationship
F
Power (Fv)
v
30 vmax
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Whole Muscle
Muscle Attachment - Tendons
Fusion b/w epimysium and periosteum
Tendon fused with fascia
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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
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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

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Functional Muscle Groups
Whole 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

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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

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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
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Muscular Action
Whole Muscle

• 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

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Whole Muscle
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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

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Elbow Actions
Whole Muscle

• 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

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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
drop-stop-pop action with only an 8-12 drop
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Number of Joints Crossed
Whole Muscle

• 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

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Multiarticular Muscles
Whole Muscle

• can reduce the contraction velocity
• can transfer energy between segments
• can reduce the work required of single-joint
  muscles
• more susceptible to injury

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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

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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?

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Movement/Activity Properties of Muscle
Whole Muscle

• flexibility - the state of muscles length which
  restricts or allows freedom of joint movement
• endurance - the ability of muscles to exert force
  repeatedly or constantly

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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

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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

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Strength Gains
Whole Muscle
Training focuses on developing larger x-sectional
area AND developing more tension per unit of
x-sectional area
Magnitude of strength gains dependent on 1)
genetic predisposition 2) training specificity 3)
intensity 4) rest 5) volume
from an untrained state 1st 12 weeks see
improvement on the neural side via improved
innervation later see increase in x-sectional
area
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Whole Muscle
Isotonic Exercise
Isokinetic Exercise
Isometric Exercise
Training Modalities
Variable Resistance Exercise
Close-Linked Exercises
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Whole Muscle
Muscle Injury
Individuals at risk a) fatigued state b) not
warmed-up c) new exercise/task d) compensation
Greatest Risk a) 2-joint muscles b) muscles that
limit ROM c) muscles used eccentrically
Soreness v. Damage damage believed to be in
fiber soreness due to connective tissue
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Muscular Force Components
Whole Muscle

• stabilizing or dislocating component
• parallel to rotating segment
• stabilizing is toward joint
• dislocating is away from joint

• rotary component
• causes motion
• perpendicular to the rotating segment

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Muscular Force Components
Whole Muscle

• components depend on the joint angle

large rotary small stabilizing
medium rotary medium dislocating
small rotary large stabilizing
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What Causes Motion?Force or Torque?
Whole Muscle

• 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 joints axis of
  rotation

muscle force (Fm)
muscle torque (Tm)
distance between pt of application and joint
axis (dm)
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Calculation of Muscle Torque
Whole Muscle
400 N
0.03 m
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Calculation of Muscle Torque
Whole Muscle
Only the perpendicular component will create a
torque about the elbow joint so only need to
calculate this.
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Whole Muscle
Angle of Pull Affects Torque
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Whole Muscle
Size of Muscle Force Affects Torque
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Whole Muscle
Moment Arm Affects Torque
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Calculation of Muscle Torque
Whole Muscle
400 N
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
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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 - cant change
voluntarily but use of other muscles in same
functional muscle group gives a different d 3) q
- this changes throughout the ROM
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Additional Factors Affecting Torque
Whole Muscle
Muscle Force 1) level of stimulation 2)
muscle fiber type 3) PCSA 4) velocity of
shortening 5) muscle length Angle of
pull Moment arm