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Anatomy > Biomechanics > Flashcards

Biomechanics Flashcards

1
Q

Define mechanics

A

The study of forces and their effects

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2
Q

Define biomechanics

A

The study of the principles of mechanics as applied to living bodies

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3
Q

Define kinematics

A

Description and analysis of motion without reference to force

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4
Q

Define kinetics

A

Description and analysis of forces that result in motion

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5
Q

What are machines?

A

A machine is a mechanism that transmits forces from place to another, usually changing it’s magnitude

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6
Q

How do joints work as machines?

A
  • Limbs are levers
  • Muscle supplies the energy
  • Muscles cross joints (one or more) thus causing movement when they contract
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7
Q

How do levers work?

A
  • A lever is a rigid structure that transmits forces by turning at a pivot
  • Each force is spaced from the pivot by a segment called the lever arm
  • The in‐lever or effort arm (applying force) extends from the in‐force to the pivot
  • The out‐lever or resistance arm extends from the out‐force to the pivot
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8
Q

What is torque?

A

The product of Force x Lever‐arm is called the moment, torque or turning force

Each functioning lever has at least two torques:

  • in‐system or effort arm
  • out‐system or resistance arm
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9
Q

What is the equation for torque?

A

τ= Fxd

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10
Q

What is the equation for the magnitude of torque?

A

τ = Fxd sin θ

(where θ is the angle between the force applied and the axis of rotation)

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11
Q

What is the SI unit for torque?

A

Nm

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12
Q

How do lever systems work within the body?

A
  • Muscle acts on rigid rod (bone) that moves around a fixed point called a fulcrum
  • Resistance is weight of body part & perhaps an object
  • Effort or load is work done by muscle contraction
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13
Q

What is mechanical advantage?

A
  • Efficiency of a lever depends on where the forces are located in relation to the fulcrum
  • Efficiency determined by calculating the mechanical advantage (ma)
  • Length of the effort arm (or force arm) divided by the length of the resistance arm (or load arm)
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14
Q

What is the formula mechanical advantage?

A

Mechanical advantage = Effort arm/Resistance arm

(No SI units, it is a ratio)

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15
Q

When Mechanical Advantage is greater than one _?

A
  • Joint is built for Force
  • Effort arm > resistance arm
  • Torque created by the effort force is magnified by the greater effort arm
  • Raising up on your toes
  • Not usual in human body
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16
Q

When Mechanical advantage is less than one _?

A
  • Joint is Build for Speed
  • Resistance arm > effort arm
  • Greater effort force is required to overcome resistance force
  • Effort force acts over a small distance
  • Resistance force is moved over a much greater distance
  • Most of the levers in the body have MA < 1
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17
Q

What is a first order lever?

A

A lever which has the fulcrum between the effort and the resistance

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18
Q

How does a first order lever work?

A

A first order lever can produce mechanical advantage or not depending on location of effort & resistance

  • if effort is further from fulcrum than resistance, then a strong resistance can be moved
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19
Q

Give an example of a first order lever

A

Head resting on vertebral column

  • weight of face is the resistance
  • joint between skull & atlas is fulcrum
  • posterior neck muscles provide effort
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20
Q

What is a second order lever?

A

One where the load is between the efford an the fulcrum

  • Like a wheelbarrow
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21
Q

How does a second order lever work?

A

Always produce mechanical advantage (MA > 1)

  • resistance is always closer to fulcrum than the effort
  • Sacrifice of speed for force
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22
Q

Give an example of a second order lever

A

Raising up on your toes

  • resistance is body weight
  • fulcrum is ball of foot
  • effort is contraction of calf muscles which pull heel up off of floor
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23
Q

What is a third order lever?

A
  • Effort between resistance and fulcrum
  • Most common levers in the body
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24
Q

How do third order levers work?

A

Always produce a mechanical disadvantage (MA < 1)

  • effort is always closer to fulcrum than resistance

Favors speed and range of motion over force

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25
Q

Give example of third order lever

A

Flexor muscles at the elbow

  • resistance in weight in hand + weight of the limb
  • Fulcrum is the elbow joint
  • Effort in contraction of the biceps brachii muscle
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26
Q

What are the five different external types of force that biological tissues are subjected to?

A
  • Compression force
    • pressing together
  • Tension force
    • pulling a body apart
  • Shear force
    • applied parallel to surface
  • Torsion force
    • twisting a body
  • Bending deformation
    • load is applied where no direct support exists
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27
Q

How does compressive force effect the anatomic strucure?

A
  • push joint surfaces together
  • anatomic structures get shorter and wider
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28
Q

How does tension affect the anatomical structure?

A
  • tissues pulled apart
  • anatomic structures to get longer and narrower
29
Q

How does shear loading affect anatomical structure?

A

Stress applied in opposite directions on the two sides of the material causes it to
deform internally

30
Q

How does torsion effect the anatomical structure?

A
  • moment action of force about longitudinal axis of a structure
  • act on planes perpendicular to the longitudinal axis.
31
Q

How does bending affect the anatomical structure?

A
  • forces produce equal & opposite moment actions about a section of a structure
  • stretch outer surface and compress inner surface
32
Q

Which load types are normal forces for biological tissues to contend with?

A
  • Compression
  • Tension
33
Q

Which load types will do damage to biological tissues?

A
  • Shear force
  • Torsion
  • Bending
  • Compression (Too much)
  • Tension (Too much)
34
Q

What is stress?

A

Stress describes the force causing strain

35
Q

What is strain?

A

Strain described how far the molecules of a solid are being pulled apart or pushed together

36
Q

How is strain measured?

A
  • measure of deformation or change in proportions caused by the stress
  • ratio, it has no units, it is just a number

The changed length/The original length

37
Q

How is stress measured?

A
  • intermolecular resistance to a deforming force or load
  • Pascals: force per unit area (N/m2) (Newtons / square metre)

Stress = F / A

force / area

the applied force/the cross sectional area

38
Q

What is a load?

A

A load is a force applied to a material

39
Q

What does a stress/strain (load deformation) curve show?

A
  • Measures the strength and stiffnes of materials
  • Initially, a material will deform linearly, such that the deformation increases with an increase in the load
    • When the load is removed, the material will return to the initial shape, and is elastic
  • Eventually, the force exceeds the ability of the material to return to the previous state
    • Deformation becomes more permanent
    • Marked by yield point
      • Microfractures and tears appear
      • Deformation will continue without an increase in load
40
Q

What are the stages in a load deformation curve?

A
  • Elastic phase
    • Returns to previous shape when force is removed
  • Plastic phase
    • Material will partly, but not completely return to its’ previous shape
  • Failure point
    • Eventually the fracture point will be exceeded and the material will break
41
Q

What is the ratio between stress and strain?

A

Young’s Modulus (Nm-2)

(Different materials have different youngs modulus)

42
Q

How do you find strength using a Stress/Strain curve?

A

Area under the curve

43
Q

How do you find stiffness using a stress/strain curve?

A

Gradient of curve during elastic response

Modulus of Elasticity/Young’s modulus

44
Q

What is Hooke’s Law?

A

Stress is proportional to strain

(Stress = k x strain

where k = Young’s Modulus)

45
Q

Linear or Normal Stress & Strain

A
  • Perpendicular to cross axis
  • Youngs Modulus
46
Q

Shear or Tangential Stress & Strain

A

Parallel to plane of applied load

Shear Modulus

47
Q

Equation for Young’s Modulus

A

Linear stress F/A

————————— = ———————

Linear strain (L2‐L1)/L1

48
Q

Equation for Shear Modulus

A

Shear stress F/A

———————— = ————
Shear strain ø

49
Q

Describe elasticity and deformation

A
  • Elasticity is the ability to return to original shape
    • If exceeded, injury to human tissues occurs
  • Deformation is the change of shape or dimensions produced by applied forces
    • Many materials exhibit elastic deformation with moderate stress, permanent deformations results from larger stress
50
Q

Describe Stiffness

A

Stiffness is the ability to resist a force during the elastic phase

  • if a material is resistant to the force it is stiff
  • if a material cannot resist force well, it is termed flexible
51
Q

Describe ductility and brittleness

A
  • Ductile
    • capacity to absorb large amounts of plastic deformation
    • metals are very ductile
  • Brittle
    • substances that fail quickly after the plastic phase is reached
52
Q

Describe weakness and strength in materials

A
  • The strength of a material is defined by the failure point
    • load sustained before failure
  • Strength can also be assessed in terms of energy storage
    • area under the stress/strain curve
53
Q

Describe anisotropic?

A

Behaviour of material varies depending on the direction of loading

54
Q

Describe visoelastic

A

Rate at which stress forces are applied affects the stiffness

55
Q

What are the characteristics of various materials?

A
  • Flexibility/Stiffness
  • Ductility/Brittleness
  • Weak/Strong
  • Anisotropicity
  • Viscoelasticity
56
Q

What are the properties of bone?

A
  • Anisotropic Characters
  • Viscoelastic Characters
  • Compression & Tension
  • Shear forces
  • Bending forces
  • Torsion
57
Q

What are the anisotropic characters of bone?

A
  • The behaviour of material varies depending on the direction of loading
  • Bone can handle greater loads along the longitudinal axis than across the surface
  • Habitually loaded in that direction and has adapted to cope with the load
  • Structure of bone optimised for normal load‐bearing functions
  • Bone filaments lie along the internal stress lines
58
Q

What are the viscoelastic properties of bone?

A
  • Rate at which stress forces are applied affects the stiffness
  • Bone shows sensitivity to rate of stress loading
  • A quickly applied force meets with a higher resistance
  • Allows spine to withstand much greater impact forces without excessive deformation of vertebral bodies than would be the case if the same force was applied more gradually
    • Impact on vertebra when jogging
    • e.g. prolonged lifting
59
Q

How do compression and tension effect bone?

A
  • Bone seldom deformed > 3%
  • Resists compression better than tension
  • Most breaks occur because of tensile force
    • hip in a runner
    • countered by muscular forces e.g. glutius medius
60
Q

How do shear forces effect bone?

A
  • experienced during compression and tension
  • not resisted so well due to the anisotropic properties of bone
  • can easily cause injury in the knee joint epiphysial growth plate of children
  • problem as the epiphysis is the fastest growing point in the body
    • 37% of bone growth in length
61
Q

How do bending forces effect bone?

A
  • can be very destructive, as the bone experiences tension on one side, and compression on the
  • other
  • bone can withstand greater compressive force than tensile bone gives at the point of stretch
  • injury producing bending forces are produced by three or four point loads
    • when a skier falls over ski boots
    • improvement in boot manufacture and ski techniques has reduced such injury
62
Q

How does torsion or twisting forces effect bone?

A
  • magnitude of the stress increases with distance from the axis of rotation
  • maximal shear stress acts both parallel and perpendicular to the axis of the bone
  • causes bone fracture for example when throwing a ball with poor technique, or when the foot is planted and the body is rotated in a different direction
63
Q

What are the properties of hyaline cartilage?

A
  • viscoelastic material as 75% water
  • under load water exuded from the tissue
  • when loaded rapidly little time for loss of water so responds stiffly as elastic material
  • during long periods of loading (standing) it will deform squeezing water out
  • when load removed returns to original shape
  • able to resist shear forces ‐ friction from movement at joint surfaces
  • if shear loads rapidly applied, fluid does not have time to redistribute causing damage
  • adhesive & abrasive wear occurs due to surface fragments or a harder surface coming into contact with it
64
Q

What are the properties of collagen and elastin?

A
  • common to tendons, ligaments and skin
  • embedded in these tissues are collagen fibres for strength, elastin fibres for elasticity, and reticulum for bulk
  • these tissues also have ground substance properties of the tissues affected by 3 factors:
  1. orientation
  2. proportions
  3. properties
65
Q

How does orientation affect the properties of collagen and elastin?

A
  • in tendons collagen orientation is parallel, giving ability to withstand great tensile forces
  • in skin orientated more randomly and is more extendable to withstand tension, compression and shear
  • ligaments are between but with great ability to withstand tension
66
Q

How does proportions affect the properties of collagen and elastin?

A
  • Tendons are nearly all collagen
    • very large tensile forces can be tolerated without large degrees of deformation as tension
    • develops in the muscle
  • Ligaments have greater amounts of elastin
    • some ligaments such as the ligamentum nunchae are capable of elastic recovery of up to 99%
67
Q

What are the properties of collagen and elastin?

A
  • Collagen is ductile
    • absorbs large amounts of plastic deformation
  • Elastin is brittle
    • fail quickly after the plastic phase is reached
68
Q
A

Anatomy (17 decks)

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