Endurance training increases mitochondrial density and oxidative enzyme activities. Which pair of enzymes is commonly cited as examples?

Endurance training increases mitochondrial density and oxidative enzyme activities. Which pair of enzymes is commonly cited as examples?

• A. Citrate synthase and succinate dehydrogenase
• B. Lactate dehydrogenase and pyruvate kinase
• C. Hexokinase and phosphofructokinase
• D. Lipoprotein lipase and glycogen synthase

Answer: (A)

Endurance training boosts the muscle’s aerobic machinery, so scientists use enzymes that reflect mitochondrial content and oxidative capacity. Citrate synthase starts the citric acid cycle and its activity scales with how many mitochondria are present, making it a reliable marker of mitochondrial density. Succinate dehydrogenase sits in the citric acid cycle and also feeds electrons into the electron transport chain, so its activity mirrors the muscle’s oxidative power. Together, they’re classic examples shown to increase with endurance training, indicating more mitochondria and greater oxidative metabolism.

The other enzyme pairs don’t fit as well because they’re tied to glycolysis or non-mitochondrial processes. Lactate dehydrogenase and pyruvate kinase are key glycolytic enzymes linked to anaerobic energy production. Hexokinase and phosphofructokinase are early glycolysis steps. Lipoprotein lipase and glycogen synthase relate more to lipid processing and glycogen storage, not the mitochondrial oxidative system.