block 5-skeletal muscle fatigue Flashcards
(18 cards)
what is fatigue?
- ‘failure to maintain the required or expected force’
- ‘any exercise-induced reduction in the ability to exert muscle force or
power regardless of whether or not the task can be sustained’
- ‘failure to continue working at a given exercise intensity’
Creatine Kinase Reaction (Phosphagen
System)
PCR + ADP + H+ = ATP + Cr
- Main disadvantage of this system is that it has limited capacity
- If no other energy source is available to the muscle, it will fatigue very rapidly.
- During 100m sprint – first 30-50m full power can be maintained, as the race
continues speed can drop off as these stores become depleted and power output
declines - HOWEVER: recovery is quick – a second sprint can be performed after just 1-2
minutes of recovery.
What happens to the rate if anaerobic glycolysis during excerize
-Anaerobic glycolysis is a metabolic pathway that breaks down glucose into pyruvate to produce energy (ATP) without using oxygen. It is the primary source of energy during short, intense physical activity like sprinting or heavy lifting when oxygen delivery to muscles is insufficient. (to understand)
- it decreases over time is muscle fibres specjfc so decrease mainly in type 2 fibres.
- second column on image = glycolysis first = phosphocreatine levels
see lecture or simis notes
What cause fatigue In high intensity exercise e.g. sprints
- it’s not the result of depletion of energy stores. Instead, metabolic by- products seem to be important factors in the onset of fatigue
How does product inhibition cause fatigue in high intensity excersize?
In high-intensity exercise, certain metabolic products (like lactate, H⁺ ions, and ADP) build up.
These products can inhibit key enzymes in energy pathways (e.g., glycolysis), reducing ATP production — this is called product inhibition.
Additionally, accumulation of metabolic by-products (like H⁺) interferes with muscle contraction, contributing to fatigue.
Result: Less energy and reduced muscle function, leading to early fatigue.
Lactic acid production during high intensity exercise
lactic acid dissociates into lactate and H⁺ ions:
LacticAcid → Lactate + H+
Lactate itself is not harmful and may even help clear H⁺ — it’s not the cause of fatigue.
The accumulation of H⁺ ions (not lactate) contributes to:
Lowered muscle pH (acidosis)
Impaired enzyme activity (e.g., in glycolysis)
Disrupted muscle contraction
Newer evidence shows that while H⁺ contributes to fatigue, it’s not the sole cause — other factors like inorganic phosphate (Pi) and calcium handling also play roles.
Studies on isolated muscle fibers show force production drops when exposed to high lactate and H⁺ levels.
Consequences of H+-CHEAT SHEET
▪ The acidity associated with H+ ion
accumulation causes muscle pH to fall
▪ Reduced muscle pH contributes to
fatigue through:
* Reduced activity of glycolytic enzymes
(especially PFK)
* Interference with contractile process (Ca
binding)
* Stimulation of nerve endings
The role of inorganic phosphate in the development of fatigue
- During intense exercise, Pi levels rise due to rapid ATP breakdown.
High Pi contributes to muscle fatigue in several ways:
Calcium buffering:
Pi can bind to calcium (Ca²⁺) in the sarcoplasm, reducing free Ca²⁺ available to bind to troponin.
This prevents effective cross-bridge formation between actin and myosin.
Interference with power stroke:
Pi can rebind to the myosin head before the power stroke completes, interrupting force production.
Inhibition of myosin ATPase:
High Pi slows down myosin ATPase activity, reducing the speed of ATP hydrolysis.
This slows cross-bridge cycling, making muscle contractions weaker and slower.
The role of ADP in the development of fatigue
-Accumulation of ADP during intense or prolonged muscle activity has been shown to slow the cross-bridge cycling rate.
Specifically, ADP slows the detachment of myosin from actin by competing with ATP for binding sites on the myosin head.
This delays the release phase of the cycle, ultimately reducing the speed of skeletal muscle shortening.
As a result, elevated ADP levels impair contractile efficiency, contributing to the onset of muscular fatigue.
The role of k+ in the development of fatigue
- during high intensity exercise = increased firing of action potentials = more K+ leaving the cell so it’s harder to be repolarised so causes a distruption to the action potengional propagation during muscle contraction
What are the metabolic by- products of high intensity exercise
- lactic acid/. H+; p+; K+-,ADP
How can we improve fatigue resistant during high intensity excersize
- creating monohydrate supplement increases the intracellular creatinine
and phosphocreatine stores by 20-25%
what does the body need to rely on or ATP during proplonged exercise
Need to rely on carbs for as long as possible possible as they produce energy quickly and don,t rely on ATP to break it down
Muscle glycogen storage-MAYBE CHEAT SHEET
) Sub-sarcolemma – between cell surface
membrane
2) Intramyofibrilliar – between contractile
filaments located close to the triadic
junctions of the SR and t-tubules
3) Intermyofibrilliar – between myofibrils in
contact with longitudinal part of SR
The Intramyofibrilliar store may be the most
important and is the pool that we see is the most
depleted after exercise
Depletion of this pool is associated with reduced
calcium release from the SR. The coupling
between the AP and Ca2+ in the glycogen
depleted state is damaged.
Excercise intensity snd substrate use
At low intensity (e.g., walking, light jogging):
-The body primarily uses fats as the main energy source.
Oxygen is readily available, allowing fat oxidation to meet energy demands.
As exercise intensity increases:
The use of muscle glycogen and blood glucose becomes more dominant.
This is because carbohydrates can be broken down faster than fats, even without oxygen (via anaerobic glycolysis).
At high intensity (e.g., sprinting, heavy lifting):
A large proportion of energy comes from muscle glycogen due to its quick availability and rapid ATP yield.
How do we optimise glycogen content
- have a high carb diet
Does carbohydrate feeding during excersize prevent muscle fatigue ?
Yes — carbohydrates consumed during exercise help:
Maintain blood glucose levels
Delay muscle glycogen depletion
Support continued energy (ATP) production
This can delay fatigue, especially in endurance exercise (lasting over 60 minutes).
What is the plan to increase resistance to muscle fatigue in long duration exercise
- increase the amount of time the body used carbs than fats as fuels
