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Intro to Biomechanics > Properties of Muscle > Flashcards

Properties of Muscle Flashcards

1
Q

When a muscle pulls perpendicular to an axis

A
  • It causes the joint to move

- Stabilizes the joint axis

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2
Q

Muscle tissue properties

A
  • Irritability/excitability
  • Contractility
  • Extensibility
  • Elasticity
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3
Q

Irritability/excitability

A
  • Response to chemical, electrical or mechanical stimuli
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4
Q

Contractility

A
  • Ability to contract and develop tension against resistance

- Unique to muscle tissue

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5
Q

Extensibility

A
  • Can passively stretch beyond its resting length
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6
Q

Elasticity

A
  • Ability to return to its resting length after stretching
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7
Q

Muscle shape and fiber arrantement

A
  • Affects force muscle will exert

- Influence range of that force

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8
Q

Factors influencing range of muscle force

A
  • Cross section diameter of muscle

- Ability to shorten

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9
Q

Cross section diameter of muscle

A
  • Greater cross section diameter exerts greater muscle force
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10
Q

Muscle ability to shorter

A
  • Longer muscles can shorten through a greater range

- Beneficial to move a joint through a large range of motion

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11
Q

Muscle fiber arrangement

A
  • Fibers arranged parallel to the length of the muscle

- Produce the greatest range of motion

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12
Q

Shapes of muscle

A
  • Flat
  • Fusiform
  • Strap
  • Pennate
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13
Q

Flat muscles

A
  • Thin and broad
  • Arise from aponeurosis
  • e.g. Rectus abdominus and obliques
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14
Q

Fusiform muscles

A
  • Spindle like with a central belly

- e.g. Biceps bracialis

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15
Q

Strap muscles

A
  • More uniform in diameter
  • Allows for focus on small bone insertions
  • e.g. Sartorius
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16
Q

Pennate muscles (uni, bi, multi)

A
  • Shorter fibers arranged obliquely to their tendons
  • Increases cross-sectional area of the muscle ∴ increasing its force
  • Produce the strongest contractions
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17
Q

Unipennate muscles

A
  • Fibers run obliquely from one side of the tendon only

- e.g. Biceps femoris, EDL, Tibialis posterior

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18
Q

Bipennate musles

A
  • Fibers run obliquely from a central tendon on both sides

- e.g. Rectus femoris, FDL

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19
Q

Anatomic determinants of muscle contractions

A
  • Location of bone landmarks for origins and insertions

- Action of other muscles that may affect joint movement

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20
Q

Pectineal line

A
  • Pectineus muscle
  • Adduction of thigh
  • Lateral rotation of thigh
  • Flexion of hip
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21
Q

Linea aspera

A
  • Adductor magnus

- Adductor brevis – upper 1/3 medially

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22
Q

Knee joint flexion

A
  • Muscles posterior to knee axis
  • Hamstring muscles
  • Movement in the sagittal plane
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23
Q

Prime mover (agonist)

A
  • Concentric contraction
  • Does most of the work required (primary mover)
  • “Assisters” (secondary movers)
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24
Q

Prime mover (agonist) example of knee felxion

A
  • Hamstrings, sartorius, gracilis, popliteus and gastrocnemius are all agonists, but…
  • The hamstrings are the primary mover
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25
Q

Antagonist

A
  • Eccentric contraction
  • Located on the opposite side of the joint from a prime mover
  • Opposes the action of another muscle
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26
Q

Antagonist example of knee flexion

A
  • Quadriceps oppose the hamstrings

- Knee extension

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27
Q

Flexion/stabilization

A
  • Isometric contraction
  • Steadies proximal parts while movement occurs in the distal segments
  • Provide proximal stability
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28
Q

Synergist

A
  • Compliments action of prime mover

- May be referred to as “guiding” muscles

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29
Q

Neutralizers

A
  • Neutralize the action of other muscles

- Resist specific contractions of other muscles

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30
Q

Neutralizer example

A
  • Biceps contracture

- The pronator teres would resist the supination component

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31
Q

Force coupling

A
  • Allow for rotation around an axis

- Two or more forces are pulling in different directions

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32
Q

Force coupling example

A
  • Steering with two hands
  • One hand pulls wheel up and right
  • The other pulls wheel down and left
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33
Q

Types of muscle fibers

A
  • Oxidative red fibers (type I)

- Glycolytic white fibers (type IIa, IIb/x)

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34
Q

Oxidative red fibers (type I)

A
  • Possess myoglobin
  • Higher resistance to fatigue
  • Generally produce less tension than white fibers
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35
Q

Glycolytic white fibers (type IIa, IIb/x)

A
  • Produce greater forces
  • Have a greater shortening velocity
  • Fatigue more quickly
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36
Q

Type I (slow twitch) muscle fibers

A
  • Oxidative
  • Red fibers
  • Use oxygen to generate ATP
  • Fire slower, fatigue quicker
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37
Q

Type I (slow twitch) muscle fibers are used more for

A
  • Continuous, extended contraction over a long time

- Endurance

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38
Q

Type IIA (fast twitch) muscle fibers

A
  • Oxidative
  • Intermediate fast twitch
  • Red fibers
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39
Q

Type IIA (fast twitch) muscle fibers are used more for

A
  • Sustained power activities

- Large amounts of myoglobin

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40
Q

Characteristics of type IIA (fast twitch) muscle fibers

A
  • High capacity for generating ATP
  • Fast contraction velocity
  • Resistant to fatigue
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41
Q

Type IIB(X) fast twitch muscle fibers

A
  • White fibers
  • Generate ATP by anaerobic processes
  • Highest contraction velocity
  • Fatigue easily
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42
Q

Type IIB(X) fast twitch muscle fibers are used more for

A
  • Short-duration, high intensity power bursts

- Relatively few mitochondria

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43
Q

Fiber length within the muscle affects

A
  • Magnitude of joint motion
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44
Q

Concentric contraction of a muscle is

A
  • The sum of sarcomere shortening
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45
Q

Sarcomere arrangement

A
  • Arranged in series
  • The more sarcomeres in a fiber, the longer the fiber is…
  • The more it is able to shorten
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46
Q

Actin (thin) filaments

A
  • The “I band”
  • Change length along with the sarcomere
  • Anchored at both ends of sarcomere by z disks
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47
Q

Myosin (thick) filaments

A
  • The “A band”

- Relatively constant in length during contraction

48
Q

Sliding filament theory

A
  • Myosin is able to “grab” actin filaments
  • Through cross-bridges with actin it can pull the z-bands together
  • Results in muscle shortening and concentric muscle contraction
49
Q

Angle of application

A
  • The location of the muscle on the bone and the line of pull of the muscle and limb to which the muscle attaches
50
Q

The length of the moment arm will influence

A
  • Excursion of the joint

- A muscle with a longer lever arm must be able to shorten more

51
Q

Muscles are the effort in levers

A
  • Fulcrum = joint axis
  • Resistance = load, body part being lifted
  • Effort = muscles
52
Q

Class 1 levers

A
  • Designed for balance
  • The mechanical advantage (MA) is balanced (MA = 1)
  • Force arm = resistance arm
53
Q

Class 2 levers

A
  • Mechanical advantage is greater than 1

- Force (effort) arm > resistance (load) arm

54
Q

Class 3 levers

A
  • Possess the mechanical advantage of range of motion
  • MA < 1
  • Force (muscle) arm < resistance (load) arm
55
Q

Factors that influence muscle strength

A
  • Muscle size
  • Muscle moment arm
  • Stretch of the muscle
  • Contraction velocity
  • Level of muscle fiber recruitment
  • Fiber types within the muscle
56
Q

Muscle actions on joint movements

A
  • Cause (initiate, accelerate)
  • Control (slow down, decelerate)
  • Prevent (stabilize against external forces)
57
Q

Muscle mass components

A
  • 85% muscle fibers

- 15% connective tissue

58
Q

Isotonic contraction types

A
  • Concentric

- Eccentric

59
Q

Isometric contractions

A
  • Tension is developed within the muscle
  • Joint angles remain constant
  • Considered to be static contractions (active tension)
60
Q

Isometric contractions functions

A
  • Stabilize joints

- Resist external forces

61
Q

Characteristics of isometric contractions

A
  • Length remains constant
  • No movement occurs
  • Muscle tension increases to resist gravity or other antagonistic forces
62
Q

Isometric contraction in the arm example

A
  • Biceps is maintaining elbow in flexed position (triceps is agonist)
  • Triceps is maintaining elbow in flexed position (biceps is agonist)
  • Both isometric contractions
63
Q

Isometric contractions are helpful for

A
  • Effective for sculpting
  • Help maintain strength
  • Will improve strength only in one particular position
64
Q

Active tension in muscles of isotonic contractions

A
  • Cause joint angles to change

- Control joint angle change initiated by external forces

65
Q

Isotonic contractions can involve

A
  • Lengthening of the muscle

- Shortening of the muscle

66
Q

Concentric isotonic contraction

A
  • Muscle shortens
  • Movement occurs
  • Contractions result in shortening of muscle
  • The force generated by the muscle is less than its maximum
67
Q

Eccentric isotonic contraction

A
  • Muscle lengthens
  • Antagonizes prime mover
  • Acts as brake
68
Q

Concentric isotonic contraction examlpe

A
  • Biceps is agonist causing flexion of the elbow: concentric contraction (triceps is antagonist)
  • Triceps is agonist causing extension of the elbow: concentric contraction (biceps is antagonist)
69
Q

Concentric isotonic contractions will occur when

A
  • Muscle shortens
  • Muscle develops enough force to overcome the applied resistance
  • Movements against gravity
  • Joint angle changes in direction of applied force
  • Accelerate movements of a body segment
70
Q

Muscle lengthening in eccentric contractions

A
  • The external force on the muscle is greater than its maximum
  • The muscle lengthens under active tension
  • Tensions are high, but gradually lessen to control descent of movement
  • Decelerate movement of a body segment
71
Q

Eccentric contraction examples

A
  • Biceps is controlling elbow extension; triceps is agonist or prime mover
  • Triceps is controlling elbow flexion; biceps is agonist or prime mover
72
Q

Physiologically common effects of eccentric contractions

A
  • Much of normal muscular activity occurs while lengthening

- More forceful

73
Q

Effects of eccentric contractions on muscles

A
  • Muscle injury and soreness (selectively associated with eccentric contractions)
  • Muscle strengthening (eccentric may be most beneficial)
74
Q

Common examples of movements utilizing eccentric contractions

A
  • Going down stairs
  • Running downhill
  • Lowering weights
  • The downward motion of squats, push ups or pull ups
  • Common in controlled or resisted type of movements
75
Q

Eccentric exercise set example

A
  • Begin with straight leg with the ankle in plantarflexion
  • In a controlled manner, lower foot below step edge )this dorsiflexes the ankle but eccentrically affects the tendo achilles)
  • Repeat
76
Q

Passive stretch

A
  • Muscle is lengthened while in a passive state

- Tension occurs outside the cross-bridge mechanism

77
Q

Benefits of passive stretch

A
  • Increased flexibility

- Increased blood flow to muscles

78
Q

Myosin in cross bridges

A
  • Globular end called the S1 region
  • S1 region can bend or “reach up” to grab the actin binding sites
  • The tail (S2 region) also demonstrates flexibility and rotates with S1 contraction
79
Q

Cross bridge cycle

A
  • The process is repeated
  • Myosin-actin cycling occurs
  • These myosin S1-actin bonds are the cross bridges
  • Contraction of the S1 segment (power stroke)
  • ATP is required
80
Q

Tropomyosin

A
  • Can block myosin binding to actin filament
  • It rotates around the actin filament to expose binding sites
  • Requires calcium
81
Q

Troponin

A
  • Shifts the position of tropomyosin

- Requires calcium

82
Q

Contractile component of muscle

A
  • Actin-myosin crossbridges

- 85% of muscle mass

83
Q

Parallel elastic component of muscle

A
  • Muscle connective tissue

- 15% of muscle mass

84
Q

Series elastic component of muscle

A
  • Connective tissues within the tendon
85
Q

Passive tension

A
  • Through external forces

- Muscle stretched beyond its resting length

86
Q

Active tension

A
  • Number of motor units and fibers recruited

- Greatest amount of tension: 100 to 130% of its resting length

87
Q

Muscle active tension greater than 130%

A
  • Decreased ability to develop tension
88
Q

Muscle active tension less than 50-60%

A
  • Decreased ability to develop tension
89
Q

Active length-tension curve of muscle

A
  • Bell shaped
90
Q

When active muscle is at its longest or shortest

A
  • Force is minimal

- Potential cross-bridge formation is minimal

91
Q

When active muscle is at 1/2 length

A
  • Maximum force
  • Maximum cross-bridges can be formed
  • Resting length
92
Q

Passive length-tension curve

A
  • Begins at resting length

- Tension exists in the muscle when stretched beyond its resting length

93
Q

As muscle begins to stretch passively

A
  • Tension rises slowly
  • Will then rise quickly until the yield point is reached
  • Beyond this point, injury will occur
94
Q

Total force produced by a muscle

A
  • Active Force generated by the actin-myosin cross bridging plus…
  • The Passive Force from the non-contractile elements when stretched beyond resting length
95
Q

Parallel elastic component of muscle (muscle connective tissue)

A
  • Endomysium
  • Perimysium
  • epimysium
96
Q

Endomysium

A
  • Sheath of individual muscle fibers
97
Q

Perimysium

A
  • Divides muscle into a series of “compartments”

- Made up of fascicles

98
Q

Epimysium

A
  • Surrounds the entire muscle

- Connected to the deep fascia

99
Q

Tendons

A
  • Transmit force created bymuscleto bone
  • Arise from muscle at the myotendinous junction
  • Attach to bone through the enthesis
100
Q

Tendon forms a gradient to bone

A
  • Type 1 collagen
  • Fibrocartilage
  • Cartilage
  • Unite with bone
101
Q

Purpose of tendons

A
  • Active role in joint movements
  • Increase muscle movement distance
  • Centralize strength
  • Distribute force load to several bones
  • May connect two muscles
102
Q

Example of tendon strength centralization

A
  • Achilles tendon
103
Q

Example of tendon force load distribution

A
  • Posterior tibialis
104
Q

Example of tendon connecting two muscles

A
  • Conjoined tendon of adductor hallucis
105
Q

Pulley systems

A
  • Provide directional advantage
  • The force and its magnitude remain the same on both sides
  • Change the direction of the force
106
Q

Pulley systems act as as class 1 lever

A
  • Patellar tendon

- Lateral malleolus

107
Q

Tendon shape varies

A
  • Round = respond equally to tensile loads

- Flat = resistant to compression and shear forces

108
Q

Fiber alignment of tendons may change position

A
  • Tendo Achilles
  • Soleus fibers begin deep to gastrocnemius
  • Posterior fibers rotate laterally ~90 degrees
109
Q

Series elastic component of muscle (tendon)

A
  • Parallel arranged, tightly packed collagen fibrils
  • Interlaced with elastic fibers
  • Possess a “wavy” or “crimped” appearance at rest
  • Have a proteoglycan matrix
  • Fibroblasts
110
Q

Stress-strain curve for tendon elastic region (two parts)

A
  • Section 1 = the toe

- Section 2 = Young’s modulus

111
Q

Toe section of stress-strain curve

A
  • Collagen fibers uncrimping

- Little tension

112
Q

Young’s modulus section of stress-strain curve

A
  • Fibers elongate 3-4% before the yield point
113
Q

Stress-strain cure for tendon plastic region

A
  • 4-6% additional strain until failure
114
Q

Properties of tendons

A
  • Elastin content (dry weight) ~2%

- 7-10% strain before failure

115
Q

Properties of ligaments

A
  • Elastin content (dry weight) up to 60%
  • ~15% strain before failure
  • Lower percentage of collagen
  • Higher percentage of proteoglycans and water
  • Less organized collagen fibers
116
Q

Commonalities between tendons and ligaments

A
  • Transfer forces between musculoskeletal tissues
  • Low oxygen and nutrient requirements
  • Low cell density
  • Poor regenerative capacity
  • Poor vascular supply

Intro to Biomechanics (8 decks)

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