Muscle fatigue Flashcards
What is fatigue?
Failure to maintain the required or expected outcome/task
Why are muscle fibres transient?
- Recovery is quick after force produced from contraction
- Doesn’t last
What does muscle fatigue depend on?
1) Training status
2) Task (duration and load)
3) Fibre type composition
4) Type of contraction
What does everything below the muscle constitute as?
= central
What does everything after the nerve constitute?
= peripheral
What is the spectrum of human performance?
Patients > normal > athletes (sprinters, marathon runners)
= different types of muscle fatigue experienced
What can muscle fatigue be?
1) Central
2) Peripheral
3) Both
What is the command chain?
Intention to move > activating muscle from brain > goes through spinal cord to muscle fibres > contraction
What is central fatigue?
- occurs proximal to NMJ
- may occur ± peripheral fatigue
- failure of CNS to activate muscle
1) increase inhibition
2) decrease excitation - amount of AP or e- signal you
are producing
What is peripheral fatigue?
- occurs distal to NMJ
- may occur ± central fatigue
- decreases intrinsic ability of muscle to produce force
(muscle can’t be activated then contract properly)
What are some non-invasive techniques to assess neuromuscular function?
1) Transcutaneous stimulation
2) Surface electromyography (EMG) - directly induce contraction by using nerve stimulation –> look at e- signal (how it goes through the muscle) and force produced
Why is an EMG useful?
- Gives an idea of the e- signal that is going through the membrane to the TT
- Is an indication of the AP that’s propagated inside the muscle
= can detect if something is wrong
What is an electric shock?
- only one pulse
- equivalent of a twitch
= can measure amplitude of e- signal
What happens in prolonged isometric contraction?
- Muscle length doesn’t change, sustained contraction
- Decrease in force but no change in excitation = something goes wrong after the AP goes to the TT –> so linked to calcium release or inactivation of CBs
= not related to AP propagation
What happens in prolonged exercises (running or cycling)
- Same measurements taken before + after different exercises
- A problem with the contraction e.g. calcium release and inefficient CB cycling (like isometric) –> not the excitation or APs
Why is calcium release + uptake important during muscle fatigue?
- Beginning = complete mechanism
- Release more calcium, after a while doesn’t work + lose a lot of force
What is the problem in calcium transient?
???
What is calcium transient?
The movement of calcium going in and out of the SR
What is phosphagen depletion?
Pattern of CP/ATP depletion
- Associated during intensive exercise
- CP and ATP deplete rapidly
- CP supplementation delays onset of task failure
What is glycogen depletion?
- Glycogen depletion associated with prolonged submaximal exercise
- Glycogen depletion is fibre type specific depending on intensity of exercise
- Glycogen depletion impairs ability to generate ATP
What happens when Pi accumulates?
- Pi enters SR
- Calcium - Pi precipitates by binding to SR
- Decrease free calcium* concentration
*to be released = why you don’t get a “nice” calcium transient + why the force is very low
(ATP hydrolysed = ADP + Pi)
Use electrons to produce metabolites
Where does H+ come from?
Metabolic acidosis unrelated to lactate - lowers PH
What is lactate?
- A by-product of muscle fatigue
- Doesn’t cause fatigue (only an indicator)
What happens in McArdle’s disease?
MD = genetic disease w/ muscle weakness
- Muscle phosphorylase deficiency
- Rapid muscle fatigue
- But no increase in plasma H+
- Affects an enzyme producing H+
- Fatigue quickly w/o H+ = over-contributors
