CSSD Exercise Physiology & Energy Metabolism 3 — Questions and Answers
Question 1: Respiratory exchange ratio (RER) values approaching 1.0 during steady-state exercise indicate:
- Exclusive fat oxidation
- Predominant carbohydrate oxidation (Correct answer)
- Anaerobic threshold has been exceeded
- Maximal fat burning zone
Correct answer: Predominant carbohydrate oxidation
An RER of 1.0 indicates that carbohydrate is the primary fuel because the molar ratio of CO2 produced to O2 consumed equals 1.0 for glucose oxidation.
Question 2: What physiological mechanism primarily explains the ergogenic effect of sodium bicarbonate supplementation during high-intensity exercise?
- Increased glycogen synthesis
- Extracellular buffering of hydrogen ions, delaying acidosis (Correct answer)
- Enhanced fat oxidation
- Elevated VO2max
Correct answer: Extracellular buffering of hydrogen ions, delaying acidosis
Sodium bicarbonate increases extracellular bicarbonate, creating a larger gradient for hydrogen ion efflux from muscle cells, thereby delaying intracellular acidosis and fatigue.
Question 3: Which of the following BEST describes the Cori cycle?
- Conversion of alanine to glucose in the liver during exercise
- Transport of lactate from muscle to the liver, where it is converted to glucose via gluconeogenesis (Correct answer)
- Re-synthesis of glycogen from ketone bodies
- Fatty acid esterification in adipose tissue
Correct answer: Transport of lactate from muscle to the liver, where it is converted to glucose via gluconeogenesis
The Cori cycle shuttles lactate produced by muscle to the liver, where it is converted back to glucose through gluconeogenesis and released into circulation.
Question 4: An endurance-trained athlete has a higher maximal fat oxidation rate than an untrained individual primarily because of:
- Higher plasma insulin levels at rest
- Greater mitochondrial density and upregulated oxidative enzyme activity (Correct answer)
- Lower muscle glycogen stores
- Reduced CPT-I activity
Correct answer: Greater mitochondrial density and upregulated oxidative enzyme activity
Training-induced mitochondrial biogenesis and upregulation of enzymes such as citrate synthase and β-HAD increase the capacity for aerobic fat oxidation.
Question 5: During a Wingate anaerobic power test, the primary energy system used in the first 10 seconds is:
- Oxidative phosphorylation
- Glycolytic (lactic acid) system
- Phosphocreatine (PCr) system (Correct answer)
- Beta-oxidation
Correct answer: Phosphocreatine (PCr) system
The phosphocreatine system provides rapid ATP resynthesis in the first ~10 seconds of maximal effort before glycolysis becomes the dominant pathway.
Question 6: Thermal regulation during exercise affects metabolic rate because:
- Sweat production directly generates ATP
- Elevated core temperature increases enzyme reaction rates and metabolic rate (Correct answer)
- Cooling strategies reduce glycogen use at rest only
- Hypothermia increases fat oxidation rates linearly
Correct answer: Elevated core temperature increases enzyme reaction rates and metabolic rate
For every 1°C rise in core temperature, metabolic rate increases approximately 10–13%, following Q10 kinetics of enzyme activity.
Question 7: Which hormone acutely inhibits lipolysis during the early phase of exercise onset?
- Glucagon
- Cortisol
- Insulin (Correct answer)
- Epinephrine
Correct answer: Insulin
Residual insulin levels at exercise onset suppress hormone-sensitive lipase activity, transiently inhibiting lipolysis before sympathetic drive overrides this effect.
CSSD Exercise Physiology & Energy Metabolism 3
Respiratory exchange ratio (RER) values approaching 1.0 during steady-state exercise indicate: