Lecture 10 - Exercise Physiology 2024-1.pdf Flashcards
Proposed Mechanisms
of Fatigue
“Acidosis”
- Reduced pH due to high H + and lactic acid
production during short-term, maximal
exercise; insufficient oxygen
“Neural Fatigue”
* Failure of action potential to cross the motor
neuron to muscle fibre
“Nutrient Fatigue”
* Significant reduction in glycogen content
during prolonged submaximal exercise; in
presence of sufficient oxygen
Q: What causes acidosis during short-term, maximal exercise?
A: Acidosis occurs due to a reduced pH from high hydrogen ion (H⁺) and lactic acid production when there is insufficient oxygen during short-term, maximal exercise.
Q: What is neural fatigue in the context of muscle activity?
A: Neural fatigue is the failure of the action potential to cross from the motor neuron to the muscle fiber, preventing muscle contraction.
failure
- the motor neuron might temporarily run low on neurotransmitters needed to transmit the action potential across the synapse
- repeated firing of neurons can disrupt the balance of ions (such as sodium and potassium) that are critical for generating action potentials.
- Receptor Desensitization or less responsive after excessive stimulation
- excessive exercise can also lead to central fatigue so less motor output and thus less contraction
Q: What changes occur in a fatigued muscle during isolated muscle experiments?
A: In fatigued muscle, ATP levels decrease, inorganic phosphate (Pi) levels increase (products of ATP hydrolysis), and pH decreases due to lactic acid and hydrogen ion (H⁺) production.
Q: What leads to nutrient fatigue during prolonged submaximal exercise?
A: Nutrient fatigue is caused by a significant reduction in glycogen content in the muscles, despite the presence of sufficient oxygen, during prolonged submaximal exercise.
Q: How does caffeine affect force production in fatigued muscle?
A: Caffeine stimulation can restore force production in fatigued muscle, indicating it has a positive effect on muscle performance despite fatigue.
Q: How is muscle fatigue related to calcium release?
A: Muscle fatigue is associated with impaired calcium (Ca²⁺) release from the sarcoplasmic reticulum (SR), which is essential for muscle contraction.
Q: What are the key considerations when assessing fatigue during exercise?
A:
Duration and intensity of the event.
Environmental conditions like temperature and humidity.
Fitness level of the individual, including acclimatization.
Q: What are the main metabolic causes of fatigue during exercise?
A:
Glycogen depletion: Running out of stored glycogen, which fuels prolonged activity.
Low blood sugar (CNS fatigue): Insufficient glucose to support central nervous system function.
Dehydration: Loss of fluids impairing physiological functions.
Hyponatremia (low sodium): Low sodium levels affecting muscle function and fluid balance.
GI discomfort: Gastrointestinal issues that can affect nutrient absorption and energy levels.
Q: What metabolic process is primarily used during short-term (<30 seconds) sprints?
A: Short-term sprints rely on anaerobic/oxygen-independent metabolism, which includes the breakdown of phosphocreatine (PCr) and conversion of muscle glycogen to lactate.
Q: Why would an athlete consider fat loading before exercise?
A: The idea behind fat loading is to increase the body’s ability to oxidize fat for energy, which in turn reduces reliance on glycogen stores during prolonged exercise. By increasing the enzymes involved in fat metabolism, the body becomes more efficient at using fat as fuel, potentially sparing glycogen.
Q: How practical is fat loading, and how long does it need to be effective?
A: Fat loading typically requires more than 7 days to be effective, with the first 2-3 days involving very low glycogen levels. This can be impractical for athletes because prolonged fat loading can lead to fatigue and does not necessarily enhance performance.
Q: How does fat loading affect high-intensity exercise?
A: Fat loading might negatively impact high-intensity exercise. Since fat oxidation is slower than carbohydrate metabolism, the body may not meet the energy demands of high-intensity activities as efficiently, leading to decreased performance and increased fatigue.
Q: What happens to lipid stores during prolonged exercise, and why is this significant?
A: During prolonged exercise, lipid stores are not significantly depleted; they may even increase (availability of FA) due to the body’s response to energy demands. This is important because it suggests that the body has a substantial reserve of fat that it can rely on for energy, reducing the immediate need for carbohydrates.
Q: How do ATP and blood glucose levels change during prolonged exercise?
A: Intramyocellular ATP levels generally remain stable during prolonged exercise, indicating that energy production is maintained. Blood glucose levels also do not drop substantially, which prevents hypoglycemia. However, glycogen depletion can still occur, leading to fatigue depending on the intensity and duration of the exercise.
