CSSD Exercise Physiology & Energy Metabolism 2 — Questions and Answers
Question 1: During high-intensity interval training (HIIT), which metabolic byproduct accumulates and contributes to peripheral fatigue?
- Lactate and hydrogen ions (Correct answer)
- Urea and ammonia
- Ketone bodies
- Free fatty acids
Correct answer: Lactate and hydrogen ions
Lactate accumulation alongside hydrogen ions (not lactate itself) lowers intracellular pH, impairing muscle contractile function during high-intensity exercise.
Question 2: The crossover concept in exercise physiology describes the point at which:
- Fat oxidation decreases and carbohydrate oxidation becomes the dominant fuel source (Correct answer)
- Aerobic metabolism overtakes anaerobic metabolism
- Muscle glycogen depletes and fat becomes the sole fuel
- Heart rate exceeds 85% of maximum
Correct answer: Fat oxidation decreases and carbohydrate oxidation becomes the dominant fuel source
The crossover concept (Brooks & Mercier) describes the exercise intensity at which carbohydrate oxidation exceeds fat oxidation as the predominant fuel source.
Question 3: Which enzyme is rate-limiting for beta-oxidation of fatty acids in skeletal muscle?
- Malonyl-CoA decarboxylase
- Carnitine palmitoyltransferase I (CPT-I) (Correct answer)
- Hormone-sensitive lipase
- Acetyl-CoA carboxylase
Correct answer: Carnitine palmitoyltransferase I (CPT-I)
CPT-I controls fatty acid transport into the mitochondrial matrix and is the rate-limiting step for beta-oxidation; it is inhibited by malonyl-CoA at high carbohydrate flux.
Question 4: An athlete exercising at 65% VO2max for 90 minutes is MOST likely experiencing:
- Progressive reliance on plasma free fatty acids as muscle glycogen declines (Correct answer)
- Exclusive reliance on muscle glycogen throughout
- A switch to ketone body oxidation after 45 minutes
- Constant substrate utilization with no metabolic drift
Correct answer: Progressive reliance on plasma free fatty acids as muscle glycogen declines
As muscle glycogen declines during prolonged moderate-intensity exercise, plasma free fatty acid uptake and oxidation progressively increase to spare remaining glycogen.
Question 5: What is the primary role of AMP-activated protein kinase (AMPK) during exercise?
- Promote protein synthesis and muscle hypertrophy
- Sense energy depletion and stimulate glucose uptake and fat oxidation (Correct answer)
- Inhibit mitochondrial biogenesis
- Increase glycogen synthase activity
Correct answer: Sense energy depletion and stimulate glucose uptake and fat oxidation
AMPK is activated when the AMP:ATP ratio rises, signaling low energy status and triggering pathways that increase glucose uptake (GLUT-4 translocation) and fatty acid oxidation.
Question 6: During the transition from rest to moderate exercise, oxygen consumption rises in a curvilinear fashion before reaching steady state. This period is called:
- Oxygen debt
- Excess post-exercise oxygen consumption (EPOC)
- Oxygen deficit (Correct answer)
- Ventilatory threshold
Correct answer: Oxygen deficit
The oxygen deficit is the gap between the oxygen required and the oxygen actually consumed at the onset of exercise before steady-state is achieved.
Question 7: Which substrate contributes MOST to ATP production during a 10-km road race run at approximately 80% VO2max?
- Intramuscular triglycerides
- Muscle glycogen (Correct answer)
- Plasma free fatty acids
- Blood glucose alone
Correct answer: Muscle glycogen
At ~80% VO2max, muscle glycogen is the predominant substrate because the rate of fat oxidation cannot keep pace with the high ATP demand of this intensity.
CSSD Exercise Physiology & Energy Metabolism 2
During high-intensity interval training (HIIT), which metabolic byproduct accumulates and contributes to peripheral fatigue?