CSCS CSCS: Bioenergetics of Exercise & Training 3 — Questions and Answers
Question 1: The Cori cycle describes which metabolic relationship between skeletal muscle and the liver?
- Transfer of fatty acids from liver to muscle
- Reconversion of muscle-derived lactate to glucose in the liver (Correct answer)
- Transport of amino acids for gluconeogenesis
- Exchange of ketone bodies during starvation
Correct answer: Reconversion of muscle-derived lactate to glucose in the liver
The Cori cycle shuttles lactate from exercising muscle to the liver, where it is converted back to glucose via gluconeogenesis.
Question 2: Which of the following correctly describes the relationship between exercise intensity and the respiratory exchange ratio (RER)?
- RER decreases as intensity increases
- RER approaches 1.0 when fat is the primary substrate
- RER rises above 1.0 during very high-intensity exercise due to CO2 buffering (Correct answer)
- RER is unaffected by exercise intensity
Correct answer: RER rises above 1.0 during very high-intensity exercise due to CO2 buffering
At supramaximal intensities, excess CO2 is produced as bicarbonate buffers lactic acid, driving RER above 1.0.
Question 3: Which shuttle system transfers reducing equivalents (NADH) from the cytoplasm into the mitochondria to continue aerobic ATP production?
- Carnitine shuttle
- Malate-aspartate shuttle (Correct answer)
- Cori cycle
- Urea cycle
Correct answer: Malate-aspartate shuttle
The malate-aspartate shuttle (and glycerol-3-phosphate shuttle) transfers NADH electrons across the inner mitochondrial membrane for use in the electron transport chain.
Question 4: Glycogen depletion during prolonged exercise most directly impairs performance because:
- Fat oxidation ceases entirely
- CNS glucose supply is compromised and high-intensity work capacity declines (Correct answer)
- Protein becomes the sole fuel source
- RER drops below 0.7
Correct answer: CNS glucose supply is compromised and high-intensity work capacity declines
Glycogen depletion limits both brain glucose availability (causing fatigue) and the ability to sustain high-intensity exercise where carbohydrate is the primary fuel.
Question 5: Which statement about the Q10 effect is most relevant to exercise physiology?
- Decreasing muscle temperature slows enzymatic reaction rates, reducing power output (Correct answer)
- Increased temperature inhibits oxidative phosphorylation
- Q10 applies only to fat metabolism, not carbohydrate
- Warm muscle reduces PCr breakdown rate
Correct answer: Decreasing muscle temperature slows enzymatic reaction rates, reducing power output
The Q10 principle states that metabolic rate roughly doubles per 10°C increase; cold muscle has slower enzyme kinetics, reducing force and power production.
Question 6: Which of the following best characterizes the 'crossover concept' in substrate utilization?
- The point at which fat oxidation exceeds carbohydrate oxidation at any intensity
- The exercise intensity at which carbohydrate oxidation begins to exceed fat oxidation (Correct answer)
- The transition from aerobic to anaerobic metabolism
- The point at which PCr stores are fully depleted
Correct answer: The exercise intensity at which carbohydrate oxidation begins to exceed fat oxidation
The crossover concept describes the exercise intensity at which energy from carbohydrate oxidation exceeds that from fat, influenced by training status and diet.
Question 7: During steady-state aerobic exercise at moderate intensity, the primary fate of pyruvate is:
- Conversion to lactate by lactate dehydrogenase
- Conversion to alanine via transamination
- Transport into the mitochondria and conversion to acetyl-CoA (Correct answer)
- Reconversion to glucose via gluconeogenesis
Correct answer: Transport into the mitochondria and conversion to acetyl-CoA
At moderate intensities, adequate oxygen allows pyruvate to enter the mitochondria and be oxidized to acetyl-CoA by pyruvate dehydrogenase.
CSCS CSCS: Bioenergetics of Exercise & Training 3
The Cori cycle describes which metabolic relationship between skeletal muscle and the liver?