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BIOMECHANICS > MIDTERM 2 > Flashcards

MIDTERM 2 Flashcards

1
Q

EMG uses

A

diagnose:
- muscle tingling
- numbness
- weakness cramping patterns

determine:
- nerve dysfunction
- neuromuscular junction issues
- muscle dysfunction

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2
Q

surface EMG

A

electrodes placed on skin

no muscle contact

disadvantages: oil, hair, etc.

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3
Q

mitch research

A

they normalize the stress-strain relationship
- allows comparison across tissue sizes (bcs diff siz ox tails will have diff resistance)

stress is how we normalize force to tissue size

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4
Q

subcutaneous EMG

A

under skin but over muscle

aka indwelling EMG

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5
Q

intramuscular EMG

A

b/w muscle cells

aka indwelling EMG

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6
Q

cons of indwelling EMG

A

invasive, painful

doesn’t represent whole muscle

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7
Q

how to apply EMG

A

2 electrodes for every muscle, in line of muscle fibres direction

measures electrical gradient as activity moves

1 other electrode is on ground location i.e. bone

voltage is calc b/w ground and muscle b/w electrodes

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8
Q

EMG amplitude

A

not directly tied to force produced i.e. more force not equal to higher amp

intrinsic factors:
- # active motor units, more = higher amp
- fibre composition i.e. fast twitch
- blood flow
- fibre diameter
- distance b.w fibres and electrodes (if leaner, less distance)

extrinsic factors:
- distance b/w electrodes, close = fast
- placement of electrodes
- skin preparation
- perspiration
- temperature

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9
Q

potential noise

A

noise: electrical activity that’s not from the muscle

  • mvmnt of cables/electrodes: called motion artifact
  • electrical noise i.e. lights, heart
  • equip issues
  • cross talk from other muscles
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10
Q

outcome measures - EMG timing

A

EMG determines muscle activation and control

threshold: must be reached to be activated…only look at activity w/in the threshold, bcs anything else is noise

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11
Q

outcome measure - relative muscle effort

A

you CANNOT measure force thru EMG

normalization: finding max voluntary contraction/MVC, and comparing to value recorded thru action
- see % MVC used

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12
Q

parallel fibres and EMG

A

parallel > pennate, because there’s greater shortening of the entire muscle

= larger ROM

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13
Q

pennate fibres and EMG

A

rotate around tendon, causing fibres to INCREASE (eccentric)

higher fibre/unit = more FORCE

greater the pennate angle, the LESS force is transferred

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14
Q

full wave rectification

A

generates absolute values only (only postitive)

see what looks like in book

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15
Q

filtering

A

removes noise i.e. power lines

has 3 choices:
- low pass: only low frequencies shown
- high pass: keeps high frequencies
- band pass: many singals pass

linear envelope: lets frequencies b/w 2 freqs pass i.e. stop pass stop

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16
Q

integration

A

used to calculate area under curve of the linear envelope

can continue entire contraction or reset at timed intervals

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17
Q

contractile vs noncontractile

A

contractile: parts that generate force i.e. actin, myosin

noncontractile: connective tissue i.e. epimysium, indirect force

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18
Q

passive vs active vs total force

A

passive force: AKA elastic energy… connective tissue, contirbutes when stretched

active force: from contractile units

total force: passive and active tgt

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19
Q

tension and cross-bridges

A

tension is directly related to numb of cross bridges

more bridges = more force generation

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20
Q

what happens if muscle too stretched

A

the cross bridges separate, myosin heads not connected to actin

not much tension can be generated bcs of the filaments being pulled apart

21
Q

what happens is muscle too shortened

A

fewer cross bridges can connect bcs they OVERLAP with other cross bridges

22
Q

resting length

A

partially contracted state

23
Q

when is there most force produced?

A

when the muscle is partially elongated

active force + some passive

24
Q

when is active force decreased?

A
  • when muscle too shortened
  • when muscle too elongates

active force max at resting

25
Q

force-velocity relationship

A

varies depending on direction of mvmnt

26
Q

why does force change w velocity?

A
  1. inefficient coupling of cross bridges, leads to dec force production
    - takes time for myosin to attach 10ms, faster mvmnt = dec force
  2. fluid viscosity: causes viscous friction
    - velocity inc = viscosity inc
    - fluid’s resistance to stress/deformation
    - friction = iinternal force the muscle must overcome
27
Q

concentric and force-velocity

A

as velocity of shortening INC, force DEC

bcs of cross-bridge coupling (there are most when at rest, dec as move)

fluid viscosity inc as velocity inc
- direction of Fr opposes direction of velocity, therefore viscosity is opposing motion

28
Q

eccentric and force-velocity

A

as velocity of elongating INC, force INC

cross-bridge: myosin forced back, bonds are stretched and causes ELASTIC ENERGY

viscosity: Fr opposes velocity, but Fr is in same direction as muscle so it moves w motion

29
Q

Fr = C x v

A

C = viscosity coefficient
v = velocity
Fr = force created by resistive vicious dampening

30
Q

concentric dampening effect

A

Fm = Fg - Fr

resultant force = force generated by muscle minus force from resistive viscosity

as force moves up, viscosity moves down

viscosity OPPOSES force of muscle (velocity aka motion)

31
Q

eccentric dampening effect

A

Fm = Fg + Fr

bcs velocity moves down, viscosity moves UP with the force of the muscle

adds to the generated force

32
Q

ground force reaction

A

ground pushes back with equal force, in opposite direction

reaction force provided by horizontal support surface

33
Q

force formula

A

force = mass x acceleration

34
Q

law of inertia

A

inertia: objects resist any change in motion state

objects will stay still until compelled to

35
Q

momentum formula

A

p = m x v

p is in kg x m/s

36
Q

law of acceleration

A

the change of motion is proportional to the force placed on it and the direction

force = mass x acceleration

37
Q

law of action-reaction

A

there is always an OPPOSITE AND EQUAL REACTION to every action

38
Q

gravity

A

9.91 m/s2

39
Q

magnus effect

A

when you spin an object, it makes a pressure gradient that causes mvmnt to move from high to low pressure

causes curved path in baseball

40
Q

force platforms

A

used to measure rxn forces X, Y, Z and their respective moments of force

limitations:
- conscious walking
- mounting i.e. cannot be moved, elevated

balance boards are cheaper alternative, less good but comparable

41
Q

pressure sensors

A

shoe insoles, allows repeated axis measurements i.e. running
- generates electrical charge responding to stress

limitations:
- only Fz, vertical loading
- slipping
- if feet too hot, confuses reading

42
Q

vertical jump graph - position

A

starts at 0, goes down as prepare to jump, up as jump, down with gravity

43
Q

phases of vertical jump

A
  1. -ve acceleration
    - ground rxn force less than body weight
  2. +ve acceleration
    - vertical force > body weight
  3. flight phase
    - gravity pulls back down
    - ground rxn force is 0 bcs in flight
  4. impact phase
    - tells info on force and acceleration
44
Q

vertical force analysis

A
  1. impact peak: initial spike, N
  2. active peaks: in N
    - 2 for walking: initial contact and pushing off when 2nd foot is down
    - 1 for running
  3. rate of loading (N/s)
    - force at impact time from contact to impact
    - force/time
    - greater force in running, why more injuries
  4. normalized values
    - removes mass from being a factor of force
    - i.e. running active peak 2200N/850N = 2.59 BWs (bodyweights)
  5. timing
    - of peaks, foot contact, toe off, etc.
    - just analyzing graph
45
Q

joint reaction forces

A

when forces cross at a joint in x,y

sum of forces on a joint

only calculated for STATIC joints, means that horizontal, vertical forces and moments = 0

46
Q

normal force

A

force b/w 2 surfaces in contact w e/o

acts PERPENDICULAR to the surface

47
Q

friction formula

A

Ff = mu x N

N is normal force

48
Q

pressure formula

A

p = f/A

a is area

measured in pascals, Pa
1 Pa = 1 N/m2

49
Q

moment formula

A

M = F x d

BIOMECHANICS (3 decks)

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