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KNPE254 > Test 2 > Flashcards

Test 2 Flashcards

1
Q

Mechanical stress

A

The internal force divided by the cross-sectional area of the surface on which the internal force acts
Ability of an object to develop a resistance to internal loading forces and to resist deformation caused by those forces

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2
Q

Tensile stress

A

Axial stress as a result of a force or load that tends to pull apart the molecules bonding the object together at the analysis plane

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3
Q

Compressive stress

A

Axial stress as a result of a force or load that tends to push or squash the molecules bonding the object together at the analysis plane

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4
Q

Shear stress

A

Transverse stress that acts parallel to the analysis plane as result of forces acting parallel to this plane
Internally resists sliding movement of one parallel layer of a material relative to the other

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5
Q

Uniaxial mechanical loads

A

Tensile
Compressive
Shear

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6
Q

Complex mechanical loads

A

Bending
Torsion
Combined loads

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7
Q

Bending

A

Counteracting tensile and compressive loads

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8
Q

Torsion

A

Torques acting about the long axis of the object at each end causing an internal torque created by the shear force btwn the molecules

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9
Q

Combined loads

A

Combination of loading configurations (uniaxial, complex)

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10
Q

Mechanical strain

A

Quantification of the deformation of a material from stress

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11
Q

Stress vs strain

A

stress measures the deforming force per unit area of the object, whereas strain measures the relative change in length caused by a deforming force

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12
Q

Linear strain

A

change in length as a result of tensile or compressive stress

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13
Q

Shear strain

A

change in orientation of adjacent molecules as a result of these molecules slipping past each other due to shear stress

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14
Q

Stress-strain relationship (elastic or young’s modulus)

A

Ratio of stress to strain (rise over run)

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15
Q

Elastic behaviour

A

occurs if an object stretches under a tensile load but returns to its original shape when the load is removed

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16
Q

Linear elastic behaviour

A

As stress increases, strain increases by a proportional amount
ex rubber band

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17
Q

Plastic behaviour

A

When a permanent deformation of an object occurs under a load
ex paper clip

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18
Q

Material strength

A

Max stress/strain a material is able to withstand before failure (breakage)

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19
Q

Yield point

A

Point of stress-strain curve where further stress will cause permanent deformation
Elastic region before, plastic region after

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20
Q

Yield strength

A

stress at the elastic limit of a material’s stress-strain curve

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21
Q

Ultimate strength

A

max stress material is capable of withstanding

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22
Q

Failure strength

A

stress where failure actually occurs

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23
Q

Ductile materials

A

large failure strains

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24
Q

Brittle materials

A

small failure strains

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25
Q

Hard materials

A

large failure stresses

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26
Q

Soft materials

A

small failure stresses

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27
Q

Toughness

A

Ability to absorb energy; area under stress-strain curve
Tougher= more energy required to break/reach failure

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28
Q

Viscoelastic materials

A

any material that exhibits both viscous and elastic characteristics (behaves as a liquid and a solid)
- bone, tendon, ligament, cartilage, muscle

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29
Q

Viscoelastic properties

A

Strain rate dependency
Stress relaxation
Creep
Hysteresis

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30
Q

Strain rate dependency

A

The rate at which you deform/strain a tissue will effect the stress it feels
Faster loading rate = more stress created

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31
Q

Stress relaxation

A

Decrease in stress under constant strain
(length held constant)

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32
Q

Creep

A

Increase in plastic strain under constant stress
(load held constant)

33
Q

Hysteresis

A

the amount of energy dissipated as a result of internal friction during mechanical loading and unloading
Ex tendon hysteresis is imp for efficiency of locomotion

34
Q

Active element of musculoskeletal system

A

Muscle tissue

35
Q

Passive elements of musculoskeletal system

A

Connective tissue (bone, cartilage, ligament, tendon)

36
Q

Anisotropic

A

having diff mechanical properties depending on the direction of load

37
Q

Isotropic

A

having the same mechanical properties in every direction

38
Q

Stiffness

A

measure of the resistance of elastic materials to deformation caused by stress
how much load a tissue can take before it deforms
slope of stress-strain curve

39
Q

Two factors affecting mechanical properties of tissues

A
  1. Activity: strength of connective tissues increases w regular use
  2. Age: Connective tissues increase in ultimate strength w age until the third decade of life where strength decreases, bones become more brittle, tendons and ligaments become less stiff
40
Q

Connective tissue

A

Composed of living cells and extracellular components (collagen, elastin, ground substance, minerals, water)

41
Q

Collagen

A

stiff (brittle)
high tensile strength (hard)
unable to resist compression

42
Q

Bone

A

Strongest and stiffest
- strongest in compression, then tensile, weakest in shear
-30-35% collagen (high tensile strength)
- 45% minerals (high compressive strength)

43
Q

Cortical bone

A

dense and hard outer layer
can handle high stress, low strain

44
Q

Elastin

A

pliant (soft)
very extensible (ductile)

45
Q

Cancellous/trabecular/spongey bone

A

Less dense, porous inner portion
can handle low stress, high strain

46
Q

Cartilage

A

can withstand compressive, tensile and shear loads
1. Hyaline: 10-30% collagen, 60-80% water
2. Fibrous: joint cavities, intervertebral discs
3. Elastic: external ear, organs

47
Q

Tendons/ligaments

A

Stiff, high tensile strength, little resistance to compression or shear
- 70% water, 25% collagen, 5% ground substance and elastin
Ligaments have a larger elastic component and their collagen fibres are arranged only near parallel compared to tendons being parallel making them less stiff and weaker than tendons
Ligaments can carry non uniaxial loads

48
Q

Muscle fibres

A

single muscle cells; encased in ct sheath (endomysium)

49
Q

Fascicles

A

bundles of muscle fibres; encased in ct sheath (perimysium)

50
Q

Whole muscles

A

bundles of fascicles; encased in ct sheath (epimysium)

51
Q

Tendons and aponeurosis

A

connect muscle to bone

52
Q

Myofibrils

A

thread like structures lying parallel to each other within muscle fibre; light and dark bands

53
Q

Sarcomere

A

contractile unit of a muscle; repeating unit of myofibril btwn the stripes (z-bands)

54
Q

Myofilaments

A

Thin: actin, troponin C, tropomyosin
Thick: myosin

55
Q

I- band

A

contains actin and z-line; light band

56
Q

A-band

A

contains actin and myosin; dark band

57
Q

H-zone

A

region of A-band containing only myosin and M-line

58
Q

M-line

A

transverse band that anchors myosin to each other

59
Q

Z-line

A

transverse band anchoring actin to each other; mark beginning and end of sarcomere

60
Q

Factors affecting muscle force production

A
  1. Length
  2. Velocity
  3. Physiological cross-sectional area
  4. Muscle geometry
  5. Activation
61
Q

Muscle force-length relationship

A

Optimal sarcomere length for force generation= 120% resting length (plateau)
Sarcomere shorter than optimal length = opposing actin filaments begin to overlap and myosin cant attach= less force (ascending)
Sarcomere contracts even shorter = actin and myosin jammed against opposite Z-band= no force produced
Sarcomere stretches longer than optimal length= thick and thin filaments spread too far apart and cant slide over each other= less force (descending)

62
Q

Passive tension

A

Developed in sarcomere and within whole muscle by stretching of connective tissues
As muscle fibre length increases and active force is decreasing, passive force component comes into play and increases total force production of muscle

63
Q

Stretching theory

A

Stretching you muscle enhances your force generating capcity by adding the passive component to the active component

64
Q

Muscle force-velocity relationship

A

the greater the shortening velocity of a muscle= the smaller the force produced
more cross bridges in release step of contraction cycle and each cross bridge spends a large proportion of the contraction time in release step so less tension is developed
ex barbell bench press

65
Q

Muscle contraction

A

As the muscle shortens during a
contraction, the cross bridges attach to the actin myofilament, pull it toward them, release it, and then reattach to it farther along its length
Cross bridge formation: Attach, pull, release and then contract

66
Q

Essentric

A

Lengthening of muscle fibres
Can produce more force than a muscle contracting concentrically (along w isometric)

67
Q

Concentric

A

Shortening of muscle fibres

68
Q

Physiological cross sectional area

A

Adding sarcomeres in parallel by increasing number of myofibrils will increase muscle diameter and cross- sectional area = STRONGER
Adding sarcomeres in series (end to end) increases length of myofibril and longer muscles can stretch and shorten over greater lengths

69
Q

Muscle geometry

A

Longitudinal vs pennate
Pennate have large cross sectional area due to the angle of their fibres and therefore can produce more force
But they have shorter fibres which limits the distance over which they can shorten

70
Q

Activation

A

Number of muscle fibres that are stimulated to contract at any given time

71
Q

Fine/precise control

A

smaller number of motor fibres per motor neuron
better for muscles

72
Q

Coarse control

A

larger number of muscle fibres per motor neuron

73
Q

Motor unit

A

a single motor neuron and all the muscle fibres w which it synapses

74
Q

How to increase activation

A
  1. Increase firing frequency of a given motor unit
    - leads to a repeated series of twitches which cause a tetanic response from a single fibre (sustained contraction w plateaued tension)
  2. Recruit more motor units
75
Q

Henneman’s size principle

A

motor units are recruited from smallest (slow twitch) to largest (fast twitch)

76
Q

Benefits of henneman’s size principle

A

Fatigue prevention: save fast twitch fibres for when needed
Fine and coarse control: allow us to apply smaller, finer forces then higher forces when needed

77
Q

Stiffness

A

measure of the resistance of elastic materials to deformation caused by stress
how much load a tissue can take before it deforms
slope of stress-strain curve

78
Q

Depth

A

An object with greater depth (and more cross-
sectional area farther from its neutral axis) is able to
withstand greater bending loads. The counteracting
tensile and compressive stresses are lower,
because they have a larger moment arm.
Under similar bending loads, the stresses in such an object
will be smaller.

79
Q

Moment arm, forces and stress

A

Ex pencil
moment arm is small, so the internal forces (and stresses)
must be large to create a large enough countering torque
An
object with a larger diameter is able to withstand greater
torsional loads since the shear stresses are smaller as a
result of the larger diameter and large moment arm

KNPE254 (1 decks)

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