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Exercise & Environment > Muscle fatigue and damage > Flashcards

Muscle fatigue and damage Flashcards

1
Q

what is muscular fatigue

A

failure to maintain the required or expected outomce/task. When you can no longer sustain a certain level of work and force is lost.

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2
Q

what is transient

A

muscle fatigue. Force can be recovered with rest

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3
Q

spectrum of human performance level

A
  • patient
  • normal
  • athlete
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4
Q

what kind of athletes have lots of fatigue

A

power atheletes

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5
Q

what kind of athletes have good fatigue resistance

A

endurance athletes

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6
Q

muscle fatigue is complex. what does it depend on?

A

training status
task - duration and load
fibre type composition
type of contraction

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7
Q

muscle fatigue is complex. what kind of fatigue is there?

A

central
peripheral
both

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8
Q

central fatigue

A

related to how you contract your muscle. Everything that happens before the neuromuscular junction

  • normally signal comes from brain through spinal chord to NMJ to make fibres contract
  • failure of CNS to activate muscles through reduced excitation or increased inhibiton
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9
Q

normal command chain for muscle contraction

A

signal from brain, through spinal chord to neuromuscular junction to make fibres contract

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10
Q

how does the CNS fail to activate muscles in central fatigue

A

reduced excitation OR

increased inhibition

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11
Q

peripheral fatigue

A

occurs after the neuromuscular junction

occurs within the muscle from reduced intrinsic ability of muscle to produce force

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12
Q

fatigue that affects command chain before the NMJ

A

central fatigue

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13
Q

fatigue that affects command chain after the NMJ

A

peripheral fatiuge

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14
Q

which fatigue is easier to ases

A

peripheral

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15
Q

method of measuring central fatigue

A

transcutaneous stimulation - difficult and controversial

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16
Q

method of measuring peripheral fatigue

A

surface electromyography

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17
Q

pathway of action potential after the NMJ

A
  • AP goes through muscle membrane
  • AP signal becomes mechanical
  • calcium released and binds to thin filament for myosin actin interactions
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18
Q

theory of surface electromyography

A

separates between electrical and mechanical signal of muscle stimulation to tell ig there is a problem with AP not propagating the muscle properly,, or a fault with mechanical signal

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19
Q

process of surface electromyography

A
  • electrodes on skin surface of muscles
  • electrical shock induces twitches causing contraction
  • contraction is electrical signal followed by mechanical signal
    EMG measures M wav and peak twitch
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20
Q

M wave

A

shows electrical signal of muscle contraction, will go up and down like AP

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21
Q

peak twitch

A

when muscle contracts

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22
Q

results of EMG

A

perform before exercise to obtain M wave and peak twitch
perform post exercise to compare
- if M wave change, there’s a change in electrical signal
- if peak twitch change, mechanical signal has changed therefore force output

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23
Q

causes of peripheral fatigue

A
  • problem in calcium transient, caused by…
  • huge increase in Pi
  • H+ accumulation
  • phosphagen depletion
  • glycogen depletion
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24
Q

problem in calcium transient

A

a) normal calcium release at beginning of exercise
b) uptake of calcium because muscle not fatiguing. increased calcium release and uptake to activate muscles
c) normal Ca release as muscle begin to fatigue and so calcium reduced to normal
d) no calcium released
- force reduces as calcium release reduces

25
Q

why does calcium release change during exercise?

A

energy is needed for th muscle in the form of ATP
- muscle fatigue when there is not enough ATP fo contraction
-or muscle fatigue becuase of by-products from ATP production
….
these affect calcium

26
Q

what happens to [Pi] during exercise

A

huge increase, 2mM to 30mM

27
Q

effects of increased [Pi]

A
  • Pi enters sarcoplasmic reticulum
  • forms precipitate with calcium
  • decreased free [Ca2+]
  • less myosin head activation
28
Q

what forms a precipitate with Ca causing fatigue

A

Pi

29
Q

effects of increased H+ during exercise

A

pH changes from 7 -> 6.2

  • acidic condition through metabolic acidosis
  • causes fatigue
30
Q

change in pH during exercise

A

7 -> 6.2

31
Q

what causes metabolic acidoses

A

H+ accumulation

NOT lactate

32
Q

what does lactate have to do with muscle fatigue

A

lactate production does not cause acidosis or muscle fatigue
lactate occurs during fatigue, but does not cause it
- lactate is a marker of fatigue

33
Q

what is a marker of muscle fatigue

A

lactate

34
Q

McArdke’s disease

A

proof that muscle fatigue can occur independent of H+ accumulation
- muscle phosphorylase deficiency
- rapid muscle faitgue
- no H+ increase
= H+ contributes to fatigue but not whole cause

35
Q

phosphates depletion

A

Patterns of CP/ATP depletion

  • depletion associated with intense exercise
  • CP and ATP deplete rapidly
  • CP supplementation delays onset of task failure
36
Q

CP

A

Creatine phosphate

37
Q

Glycogen depletion

A
  • associated with prolonged sub maximal exercise
  • fibre type specific,, depending on type of exercise
  • impairs ability to generate ATP
38
Q

which fibre type fatigues more quickly

A

TII

39
Q

what contraction causes more fatigue

A

eccentric exercise

  • causes more fatigue
  • contraction reduces after exercise more
  • damages muscle so recovery not 100%

An eccentric contraction is the motion of an active muscle while it is lengthening under load

40
Q

what contraction fatigues less

A

isometric exercises

  • contraction doesn’t decrease as much after exercise
  • returns to normal more quickly after rest
41
Q

how is muscle damage diagnosed

A

increased myoglobin and creatine kinase levels CK

42
Q

how is muscle damaged characterised

A

structural and functional changes

vary between individuals, depending on genetics and whether body is used to eccentric exercise

43
Q

what do increased myoglobin and creatine kinase levels indicate

A

muscle damage

44
Q

different structural and functional changes of muscle damage

A
  • sarcomeric disruption
  • z-disc streaming
  • t-tubule disruption
  • calpaan activation
  • increased inflammation
  • increased activation of satellite cells
45
Q

positive changes of muscle damage

A

increased activation of satellite cells

46
Q

sarcomeric disruption

A

eccentric exercise puts lots of pressure on sarcomeres to lengthen the muscles.
Even when shortening muscle, the great pressure causes lengthening
- the resistant of muscle shortening causes stretching which disrupts S

47
Q

z-disc streaming and t-tubule disruption

A
  • t-tubule is where AP propagation goes to SPR
  • usually vertical lines, but loss of z-line causes longitudinal orientated t-tubule segments
  • disruption to t-tubules disrupts all ion channels
48
Q

what causes leaking muscle ion channels

A

disruption to t-tubules

49
Q

calpain activation

A

leaky ion channels mean More calcium is released that normal and excess goes to the mitochondria which is a calcium buffer, but in the long term high Ca will degrade muscle proteins like membranes

Calpain is calcium-activated protease which exists as an inactive proenzyme in the cytosol. When intracellular calcium level is overloaded, it triggers to convert the proenzyme to its active form. Activated calpain then cleaves cytoplasmic and nuclear substrates, leading to apoptosis.

50
Q

what is calpain

A

protease activated by Ca2+

Calpain is calcium-activated protease which exists as an inactive proenzyme in the cytosol. When intracellular calcium level is overloaded, it triggers to convert the proenzyme to its active form. Activated calpain then cleaves cytoplasmic and nuclear substrates, leading to apoptosis.

51
Q

what is a calcium buffer

A

mitochondria

52
Q

what does longterm high calcium causes

A

degradation of muscle muscle proteins

53
Q

what activates calpain

A

Ca2+

54
Q

what is used to show increased membrane permeability

A

Evans Blue Dye

55
Q

increased inflammation

A

7-10 days after eccentric exercise. More blue dots = more mono nucleated cells = more inflammation
return to normal after 20 days

56
Q

what are more mono nucleated cells a sign of

A

inflammation following eccentric exercise. appear 7-10 days after and return to normal after 20 days

57
Q

increased activation of satellite cells

A

long term benefit of eccentric exercise

  • produces more muscle fibres for muscle growth
  • hypertrophy
58
Q

Research supporting polymorphisms of muscle fatigue

A

single nucleotide polymorphisms (SNP)
small differences in coding causing slightly different proteins to be produced
- some of these different proteins are advantageous
e.g alpha actinic in the Z disc is more resistant to exercise

Exercise & Environment (14 decks)

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