4 Muscle Fatigue Flashcards
Describe the differences between isometric, isotonic and eccentric muscle contractions
Isometric: when muscle is under tension (contracted) at a fixed length
Isotonic: muscle changes in length but tension is constant throughout movement
Eccentric: lengthening of muscle under tension
Describe what Muscle Fatigue is and its determinants and types of fatigue
Muscle Fatigue: is a decline in peak force production and muscle power output associated with intense or prolonged muscle activity
Muscle fatigue depends on:
- intensity & duration
- muscle fibre type
Types of fatigue:
- High Frequency fatigue
- Metabolic fatigue
- Long Duration fatigue
What is a motor unit?
A motor unit is a motor neuron and all the muscle fibres that it innervates
What is the difference between a muscle twitch and tetanus?
A twitch is a single contraction, a twitch summation is when there is a second stimulation before the muscle is fully relaxed. A tetanus is when there is constant stimulation of the muscle with no chance to relax producing a large force.
What are the by-products/ results of intense exercise in Type II fibres?
- increase phosphate
- lactate
- H+
- Mg2+
- ADP
- AMP
- decreased ATP
- changes in pH
- Cr
Describe how inorganic phosphate is the main cause of Metabolic Fatigue in muscle fibres
Phosphate is produced at the SR, RyR1, contractile proteins and T-tubles. Phosphate crosses into SR where there is a high concentration of Ca2+, forming calcium phosphate ( a precipitate) making Ca unavailable for release and thus unable to work on contractile proteins
Describe how decreased ATP availability effects RyR1
MgATP splits so that ATP can be utilised. During fatigue ATP diminishes and there are high concentrations of Mg and ADP. ATP allows RyR1 receptors to open, and a decrease of this makes it harder for these receptors to open. Mg2+ also binds to the inhibitory sites of RyR1 to prevent opening.
What is the most common form of ATP in muscle cells
Magnesium ATP (MgATP)
Explain the role of Chloride in the resting membrane potential of the muscle and its excitability
Chloride makes the cell repolarize more quickly and return it to resting levels, but have little effect on the membrane potential. However adicdosis causes the Cl- channels to close and essentially reduce their ability to relax.
Explain Long Duration Fatigue
Eccentric muscle contractions involve the muscles lengthening under tension. This causes structural damage to normally quite structured and organised cell. The T-tubules move away from the SR, which disrupts excitation-contraction coupling. High levels of intracellular Ca2+ cause damage to contractile proteins. This structural repair can take days to heal.
Give examples of 5 metabolic changes and their effects in an exercising muscle cell
- Increases in inorganic phosphate (Pi) and magnesium ions (Mg2+) decrease contractile function
- Pi reduced Ca2+ in the Sr by forming a precipitate
- ADP ( and AMP) compete with ATP on binding sites of RyR1, which reduces RyR1 opening
- Increase Mg2+ inhibits RyR1 from opening
- Increases in H+ reduces pH
Explain why Lactic Acid is NOT a cause of fatigue
There is a correlation between lactic acid and fatigue however it is not the cause. Lactic acid can be converted to pyruvate and utilised for energy. Lactic acid also stimulates glucose production by liver and the release of human growth hormone.
Explain High Frequency Fatigue
High-frequency fatigue is characterized by an excessive loss of force at high frequencies of stimulation and rapid recovery when the frequency is reduced. A buildup of extracellular K+ in T-tubules effects it’s ability to depolarize the membrane.
Explain the role that caffeine plays in Metabolic Fatigue
Caffeine is a RyR1 agonist which assists in opening RyR1 channels. When fatigue occurs caffeine can increase contractions by opening the channels and counteract whatever is inhibiting the RyR1 channels (usually Mg2+)
What are 5 characteristics of Slow Twitch Muscles Fibres
- High mitochondrial density (giving red colour)
- High resistance to fatigue
- Slow twitch speed
- Low twitch force
- High capillary density
- Low glycogen content
- High oxidative enzyme capacity
