Muscle fatigue and damage Flashcards
what is muscular fatigue
failure to maintain the required or expected outomce/task. When you can no longer sustain a certain level of work and force is lost.
what is transient
muscle fatigue. Force can be recovered with rest
spectrum of human performance level
- patient
- normal
- athlete
what kind of athletes have lots of fatigue
power atheletes
what kind of athletes have good fatigue resistance
endurance athletes
muscle fatigue is complex. what does it depend on?
training status
task - duration and load
fibre type composition
type of contraction
muscle fatigue is complex. what kind of fatigue is there?
central
peripheral
both
central fatigue
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
normal command chain for muscle contraction
signal from brain, through spinal chord to neuromuscular junction to make fibres contract
how does the CNS fail to activate muscles in central fatigue
reduced excitation OR
increased inhibition
peripheral fatigue
occurs after the neuromuscular junction
occurs within the muscle from reduced intrinsic ability of muscle to produce force
fatigue that affects command chain before the NMJ
central fatigue
fatigue that affects command chain after the NMJ
peripheral fatiuge
which fatigue is easier to ases
peripheral
method of measuring central fatigue
transcutaneous stimulation - difficult and controversial
method of measuring peripheral fatigue
surface electromyography
pathway of action potential after the NMJ
- AP goes through muscle membrane
- AP signal becomes mechanical
- calcium released and binds to thin filament for myosin actin interactions
theory of surface electromyography
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
process of surface electromyography
- 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
M wave
shows electrical signal of muscle contraction, will go up and down like AP
peak twitch
when muscle contracts
results of EMG
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
causes of peripheral fatigue
- problem in calcium transient, caused by…
- huge increase in Pi
- H+ accumulation
- phosphagen depletion
- glycogen depletion
problem in calcium transient
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
why does calcium release change during exercise?
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
what happens to [Pi] during exercise
huge increase, 2mM to 30mM
effects of increased [Pi]
- Pi enters sarcoplasmic reticulum
- forms precipitate with calcium
- decreased free [Ca2+]
- less myosin head activation
what forms a precipitate with Ca causing fatigue
Pi
effects of increased H+ during exercise
pH changes from 7 -> 6.2
- acidic condition through metabolic acidosis
- causes fatigue
change in pH during exercise
7 -> 6.2
what causes metabolic acidoses
H+ accumulation
NOT lactate
what does lactate have to do with muscle fatigue
lactate production does not cause acidosis or muscle fatigue
lactate occurs during fatigue, but does not cause it
- lactate is a marker of fatigue
what is a marker of muscle fatigue
lactate
McArdke’s disease
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
phosphates depletion
Patterns of CP/ATP depletion
- depletion associated with intense exercise
- CP and ATP deplete rapidly
- CP supplementation delays onset of task failure
CP
Creatine phosphate
Glycogen depletion
- associated with prolonged sub maximal exercise
- fibre type specific,, depending on type of exercise
- impairs ability to generate ATP
which fibre type fatigues more quickly
TII
what contraction causes more fatigue
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
what contraction fatigues less
isometric exercises
- contraction doesn’t decrease as much after exercise
- returns to normal more quickly after rest
how is muscle damage diagnosed
increased myoglobin and creatine kinase levels CK
how is muscle damaged characterised
structural and functional changes
vary between individuals, depending on genetics and whether body is used to eccentric exercise
what do increased myoglobin and creatine kinase levels indicate
muscle damage
different structural and functional changes of muscle damage
- sarcomeric disruption
- z-disc streaming
- t-tubule disruption
- calpaan activation
- increased inflammation
- increased activation of satellite cells
positive changes of muscle damage
increased activation of satellite cells
sarcomeric disruption
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
z-disc streaming and t-tubule disruption
- 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
what causes leaking muscle ion channels
disruption to t-tubules
calpain activation
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.
what is calpain
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.
what is a calcium buffer
mitochondria
what does longterm high calcium causes
degradation of muscle muscle proteins
what activates calpain
Ca2+
what is used to show increased membrane permeability
Evans Blue Dye
increased inflammation
7-10 days after eccentric exercise. More blue dots = more mono nucleated cells = more inflammation
return to normal after 20 days
what are more mono nucleated cells a sign of
inflammation following eccentric exercise. appear 7-10 days after and return to normal after 20 days
increased activation of satellite cells
long term benefit of eccentric exercise
- produces more muscle fibres for muscle growth
- hypertrophy
Research supporting polymorphisms of muscle fatigue
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
