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Biomechanics - Burn > Facts and Methods > Flashcards

Facts and Methods Flashcards

1
Q

Why do animals lie in roughly the same size dimension?

A

Small scale - electromagnetism dominates (10^-9)

Large scale - gravitation dominates (10^9)

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2
Q

Similar definition

A

Dimensionless products formed from measurements on individual systems have the same value for all similar systems.

any measurement on A is related to the equivalent measurement on B by a single scale factor

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3
Q

Geometric similarity

A

Similarity in length [L]

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4
Q

Temporal similarity

A

Similarity in time [T]

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5
Q

Inertial similarity

A

Similar in mass [M]

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6
Q

Kinematic similarity

A

Geometric (length) and temporal (time) similarity

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7
Q

Dynamic similarity

A

Geometric (length), temporal (time) and inertial (mass) similarity

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8
Q

Volume/area

A

Ratio that increases with size [L]

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9
Q

Consequence of increasing size (strength)

A

mass ∝ volume (L^3), weight (F) = mg, stress = F/A

As size increases, the stress experienced because of its own weight also increases

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10
Q

material strength:density

A

Relationship limiting max height of self supporting structures

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11
Q

How can we maintain strength with increased size?

A
  • increase strength density of materials (maintain geometric similarity) (increase bone strength)
  • decrease relative load experienced by the structure (reduced running speed/jump height)
  • increase dimensions disproportionately
  • change system design
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12
Q

Aim of allometry

A

Compare rate of change of a parameter of interest with a parameter that represents animal size (mass)

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13
Q

Form of allometric equation

A 
y=am^b
y - parameter of interest
a - proportionality constant
m - measure of size (mass)
b - scaling component
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14
Q

How do you form an allometric equation?

A
  • collect pairs of measurements from animals that vary in scale
  • use non-linear regression to fit allometric model
  • plot data and log transform it to get linear relationship
  • intercept = log(a), gradient = b
  • can construct confidence interval for accuracy
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15
Q

Define muskoskeletal tissues

A

structural materials from which the vertebrate body is constructed ( bone, cartilage, ligament, tendon, muscle etc)

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16
Q

Explain effective mechanical avantage

A

Ratio r/R relates muscle force to ground force
F_m x r/R = G
- F_m - muscle force
- G - ground reaction force
Reduces muscle force for larger animals because they stand more upright
Biewener (1989) - EMA scales with positive allometry

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17
Q

Why does ground reaction force increase with running speed?

A

At faster speeds, proportion of stride for which the foot is in contact with the ground (duty factor) decreases, so GRF increases with speed
- can compensate for size by reducing top running speed and therefore peak loads of the legs

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18
Q

What is the Froude No?

A

Non - dimensional speed

v^2/(gL), relates running speed with leg length and gravitational acceleration

Walk to run transition occurs at same Froude No for different sized animals

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19
Q

Define maintenance power

A

Rate of energy consumption during rest

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20
Q

Define total metabolic power

A

Rate of energy consumption during locomotion

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21
Q

Define net metabolic power

A

Total power - maintenance power, power used for locomotion

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22
Q

Define specific power

A

Power/body mass

23
Q

Define net cost of transport

A

Derivative of net metabolic power wrt speed to yield amount of energy to move a unit distance

24
Q

What is the citric acid cycle

A

Process of mitochondria converting stored energy (fats and carbs) into ATP

25
Q

What is oxygen transport?

A

Process of oxygen being transported from air to mitochondria

Air - respiratory system - cardiovascular system - musculoskeletal system

26
Q

Overarching theory to measure metabolic power

A

During aerobic glycolysis, rate of oxygen consumption ∝

metabolic power

27
Q

List 3 ways to measure oxygen consumption experimentally

A

Douglas bag technique
Open Flow system
Breath by breath open flow

28
Q

Describe the Douglas bag technique

A

Collect expired air in a bag over several minutes
Use a gas analyser to find partial pressures and volume of the gas, calculate O2 and CO2 levels
Compare to environment and number of breaths taken to calculate metabolic power
+ cheap and simple
- bag can be large
- valves and tubing can increase work of breathing
- experiment must be steady state (works on averages)

29
Q

Open flow system technique (metabolic power)

A

Animals wears loosely fitting mask - wide diameter pipe - mixing chamber - long straight pipe (laminar flow) - driving fan
Gas analyser samples flow in laminar pipe
Compare with flow rate and environment to get O2 consumption
+ works with animals with difficult to design airtight masks
+ doesn’t increase work to breathe

30
Q

Breath by breath open flow technique (metabolic power)

A

A sensitive gas analyser is integrated into the mask and calculates the co2 and O2 per breath for real time metabolic power calculation.
Advantages - Real time results
Disadvantages - Expensive and difficult to miniaturise

31
Q

Define aerobic limit

A

Max rate O2 transport system can provide O2 to muscles

32
Q

Describe 3 models for approximating mechanical energy in animal locomotion

A
  • Linked segment model - animal is a single lumped mass (sum of potential and kinetic energy over time)
  • Inverted pendulum - above model but a rigid strut is added to represent the leg
  • Spring loaded inverted pendulum model (SLIP) - represents the leg as a stiff, lossless linear spring (most accurate) (only investigates outcomes)
33
Q

Describe a technique to calculate mechanical energy by imagining the body a series of rigid linked segments

A

(1) assuming the animal can be modelled as a system of linked rigid segments
(2) obtaining morphometric information about the segments from cadaveric dissection
(3) obtaining the movement of the segments using optical motion capture
(4) calculating the instantaneous mechanical energy for each frame of the optical motion capture data as a the sum of gravitational potential and kinetic energy

Total energy = grav pot + angular kin + linear kin

34
Q

Define internal and external work

A

Internal work - energy to move limbs relative to body

External work - energy to move limbs relative to the ground

35
Q

Efficiency of muscle

A

20 - 30%

36
Q

Why can larger animals be considered more efficient?

A

Specific metabolic energy reduces with size

Specific mechanical energy invariant with size

37
Q

Describe the structure of a muscle

A

Actin and Myosin proteins

Myosin/Actin - myofibrils - muscle fibre - fibre bundle - muscle

38
Q

Describe the structure of actin and myosin

A

Both powered by synthesised ATP
actin - long twisted filaments in RH helix
myosin - stick like part with 2 rounder heads

39
Q

Describe the cross bridge cycle

A

Powered by ATP hydrolysed to ADP + P

1) An ATP molecule has just been split, releasing energy. and the myosin head binds to the actin filament.
2) The myosin cranks pulling the actin filament along relative to itself (the power stroke). ADP and P are released.
3) This allows an ATP molecule to bind at which point the myosin separates from the actin filament.
4) ATP is split into ADP and P causing the myosin molecule to flatten out again ready for another power stroke.
5) Process repeats during contraction

40
Q

What are the different types of muscle contraction

A

Concentric contraction - Shortening contraction required to produce mechanical work
Isometric contraction - Force generation with no net work
Eccentric contraction - Lengthening contraction to absorb mechanical work

41
Q

What is the stroke length and forced produced by a single myosin molecule?

A

5nm producing about 5pN of force.

42
Q

What type of fibre orientation is fast?

A

Parallel fibres

43
Q

What type of fibre orientation is strong?

A

Pinnate fibres

44
Q

Name a non-invasive technique for measuring muscle activation and what does it do?

A

Surface EMG

  • Measures the electrical stimulation of a muscle
  • Can reveal which muscle is used for which activity
  • Ok for surface muscles but can suffer from noise for deeper muscles
45
Q

Name an invasive technique for measuring muscle activation and what does it do?

A

Indwelling EMG

  • For deep muscles
  • Needs precise placement
46
Q

Name a non-invasive technique for measuring muscle force and what does it do?

A

Inverse dynamics

  • Involves placing markers on external surface of subject and tracking using video processing software
  • Affected by skin movement which can lead to large errors
  • Can’t distinguish between muscles in a group
47
Q

Name an invasive technique for measuring muscle force and what does it do?

A

Tendon buckle force transducers.

  • Small force transducers that attach to tendon
  • Can damage tendon of the subject.
48
Q

Name a non-invasive technique for measuring muscle length and what does it do?

A

Ultrasound

  • Measure fasicle and tendon length changes
  • Only surface muscles
  • Image processing is difficult
  • Skin movement can be a problem
49
Q

Name an invasive technique for measuring muscle length and what does it do?

A

Sonomicrometry

  • Calculates distance using time taken between emission and receiving and a known speed of sound.
  • Can measure length changes of a single fasicle
50
Q

Why would animals be dynamically similar during locomotion?

A
  • They are optimising the same quantity.

- A single form or function gave the greatest amount of optimisation by a significant amount.

51
Q

Why are bones more likely to fail in bending than compression?

A
  1. Bones are not perfectly straight along their length.
  2. Loads are not exactly aligned with the long axis of the bone.
  3. Cylinders are stronger under compression than bending.
52
Q

In what 3 ways are animals at equal Froude numbers dynamically similar?

A

Relative stride length (stride length/leg length)
Relative peak force (peak vertical force on leg/body weight)
Duty factor (time per stride that foot is in contact with the ground/time for the stride)
(Alexander and Jayes 1983).

53
Q

Define positive and negative allometry

A

If the scaling exponent is greater than that required for similarity the parameter of interest is said to exhibit positive allometry, if it is less than that required for similarity it is said to exhibit negative allometry.

Biomechanics - Burn (5 decks)

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