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Exercise & Environment > Muscle fibre heterogeneity and performance > Flashcards

Muscle fibre heterogeneity and performance Flashcards

1
Q

composition of endurance athlete

A
  • low muscle mass
  • slow twitch muscle composition
  • low power output maintained
  • high fatigue resistance
  • adapted CV and respiratory systems
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2
Q

composition of sprinters

A
  • large muscle mass
  • fast twitch muscle composition
  • high power output that is instantaneous
  • low fatigue resistance
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3
Q

muscle classifications (new)

A
  • colour
  • twitch characterisitics
  • twitch & fatiguability
  • contractile & metabolic
  • myosin ATPase activity
  • molecular motor
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4
Q

early muscle classifications

A
  • colour
  • twitch characterisitics
  • twitch & fatiguability
  • contractile & metabolic
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5
Q

different muscle colours

A 
red = slow, high myoglobin content 
white = fast, low myoglobin content
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6
Q

what gives muscle its colour

A

myoglobin content

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7
Q

colour of fast muscle

A

white

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8
Q

colour of slow muscle

A

red

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9
Q

which muscle has high myoglobin content

A

slow, red

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10
Q

what determines the speed of a twitch

A
  • activation caused by release of calcium from SR

- cross-bridge kinetics of myosin ATPase and isoform composition

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11
Q

can you activate one muscle fibre

A

no, you can activate one motor unit

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12
Q

characteristics of slow fibre

A

has not time to relax = fused twitches at lower frequenies

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13
Q

characteristics of fast fibre

A

has time to relax giving unfused at higher frequencies

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14
Q

how do fast and slow fibre twitch force compare

A

high frequency of stimulation is needed of fast fibres to give some force as slow fibres

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15
Q

different types of twitch fatiguability

A

based on selective activation of motor units

  • slow-fatigue resistant SFR
  • fast-fatigue resistant FFR
  • fast-fatiguable FF (force is reduced sooner)
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16
Q

contractile and metabolic classification

A 
based on:
- speed of contraction 
- substrate and enzyme characteristics 
called:
- slow twitch
- fast twitch oxidative
- fast twitch glycolytic
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17
Q

different types of metabolic enzymes for contraction

A

oxidative (HAD, SDH, CS)

glycolytic (LDG, PFK, PHOS)

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18
Q

enzymes of slow twitch

A

high oxidative

low glycolytic

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19
Q

enzymes of fast twitch oxidative

A

medium oxidative

medium glycolytic

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20
Q

enzymes of fast twitch glycolytic

A

low oxidative

high glycolytic

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21
Q

myosin ATPase activity characterisation

A

low [ATPase] in slow fibres
high [ATPase] in fast fibres

acid inhibits fast fibres
base inhibits slow fibred

using ATPas histochemistry with pre-incubation at different pH to identify fibre types

  • slow are dark at low ph, light at high pH
  • fast A and B are dark at high and light at pH 4.4
  • fast A is dark at 4.6
  • fast B is light at 4.6
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22
Q

molecular motor classification

A

heavy chain myosin isoforms
MHC-I
MHC-IIA
MHC-IIX

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23
Q

Three overall groups of muscle fibres

A

slow
fast
fastest

24
Q

SLOW

  • colour
  • twitch characterisitics
  • twitch & fatiguability
  • contractile & metabolic
  • myosin ATPase activity
  • molecular motor
A
  • colour = red
  • twitch characterisitics = ST
  • twitch & fatiguability = ST
  • contractile & metabolic = SO
  • myosin ATPase activity = Type I
  • molecular motor = MHC-I
25
Q

FAST

  • colour
  • twitch characterisitics
  • twitch & fatiguability
  • contractile & metabolic
  • myosin ATPase activity
  • molecular motor
A
  • colour = white
  • twitch characterisitics = FTa
  • twitch & fatiguability = FFR
  • contractile & metabolic = FO
  • myosin ATPase activity = Type IIa
  • molecular motor = MHC-IIa
26
Q

FASTEST

  • colour
  • twitch characterisitics
  • twitch & fatiguability
  • contractile & metabolic
  • myosin ATPase activity
  • molecular motor
A
  • colour = white
  • twitch characterisitics = FTB
  • twitch & fatiguability = FF
  • contractile & metabolic = FG
  • myosin ATPase activity = Type IIb
  • molecular motor = MHC-IIx
27
Q
  • colour = white
  • twitch characterisitics = FTa
  • twitch & fatiguability = FFR
  • contractile & metabolic = FO
  • myosin ATPase activity = Type IIa
  • molecular motor = MHC-IIa
A

fast muscle fibre

28
Q
  • colour = white
  • twitch characterisitics = FTB
  • twitch & fatiguability = FF
  • contractile & metabolic = FG
  • myosin ATPase activity = Type IIb
  • molecular motor = MHC-IIx
A

fastest muscle fibre

29
Q
  • colour = red
  • twitch characterisitics = ST
  • twitch & fatiguability = ST
  • contractile & metabolic = SO
  • myosin ATPase activity = Type I
  • molecular motor = MHC-I
A

slow muscle fibre

30
Q

why are there difference in metabolic and contractile functions of fibre types

A

muscles with different functional demands have different compositions

  • some muscles need fatigues resistant
  • some muscles need rapid power
31
Q

what determines expression of fibre types

A

genetics

32
Q

sprinter fibre type

A

primarily TII

33
Q

endurance athlete fibre type

A

primarily TI

34
Q

problem with removing muscle fibres for analysis

A

muscle fibres can be removed and single fibres teased out but by removing them from tendons, there is no longer a membrane potential for them to be activated for contraction

35
Q

what maintains membrane potential of muscle

A

Na+ K+

36
Q

alternative method for analysing muscle fibres

A

chemically skinned and then activated by immuring in a solution of calcium
- force is normalised at the cross section of the fibre for relative comparison

37
Q

method of analysing function of myosin

A

in vitro motility assay

- speed of actin filament sliding on a rail of myosin is calculated

38
Q

why is the speed of a rat fibre faster than human

A
  • rat sarcomere is same length as a human sarcomere
  • humans gain power from having large muscles with lots of sarcomeres in parallel
  • rats rely on high velocity sarcomeres in series because they have small muscles
  • different muscle compostions will have different optimal velocities to produce the sam power
39
Q

when all other things are equal, what does the arrangement of sarcomere determine?

A
  • force (parallel gives large CSA)
  • velocity (in series gives length)
  • power (total sarcomere gives volume)
40
Q

why does muscle power reduce with ageing

A
  • loss of MCH-II isoforms

older muscle has less fast fibres following selective atrophy and hypertrophy

41
Q

what modulates force from a whole muscle

A
  • motor unit recruitment

- rate of firing of individual motor unit (frequency)

42
Q

Henneman’s size principle

A

order of recruitment

  • muscle fibres in a single motor unit are all the same size
  • motor units are recruited on the basis of the size of their nerve cell body (smallest to largest)
  • TI recruited first then TIIa, TIIx
43
Q

are motor units recruited on basis of their size

A

yes, but of their nerve cell body size (smallest to largest)

not the size or number of fibres in the motor unit

44
Q

what gives a muscle good endurance

A

oxygen delivery

oxygen utilisation

45
Q

what determines a muscle’s oxygen utilisation

A

mitochondrion

46
Q

what gives muscles oxygen delivery

A

capillary supply

47
Q

what fibres favour endurance and why

A

Type I

  • high mitochondrial density
  • high capillary density
  • high myoglobin content
  • high TAG content
  • high oxidative enzyme activity
48
Q

how does exercise effect muscle fibre type

A

we cannot change fibre type but we can improve endurance through increased mitochondria and improved capillary performance

we can train to improve the metabolism of fibres

49
Q

three essential muscle fibre protein isoforms

A

Type I
Type IIa
Type IIx
(Type IIb in rodents)

50
Q

why doe fibres differentiations in mechanical properties

A

myosin heavy chain isoform composition
range from slow to fast
I -> IIa -> IIx

51
Q

how are TI designed for endurance (summary)

A

metabolic properties of TI designed for more oxidative metabolism because of their higher mitochondrial content

52
Q

what what does [ATPase] tell about fibre type

A

ATPase activity postively correlated with muscle contraction and so interpreted for contraction speed

  • during the cross-bridge cycle, the myosin molecule itself binds and hydrolyzes ATP during force generation
53
Q

why are muscle fibres preincubated for ATPase analysis

A
  • acid inhibts ATPase actiity in fast fibres but not slow fibres
  • basic condtions inhibit ATPase activity in slow fibres bt now fast fibres
    = dark colour shows which fibre types are present
54
Q

how does acid affect ATPase acitivty

A

inhibts it in fast fibres only

therefore dark colour in acid = slow fibres present

55
Q

how do basic conditions affect ATPase acitivity

A

inhibits it in slow fibres only

therefore dark colour in basic conditions = fast fibres present

Exercise & Environment (14 decks)

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