Why does lactic acid accumulate in the blood after sustained aerobic exercise?

Why does lactic acid accumulate in the blood after sustained aerobic exercise?

• A. Increased glycolysis with pyruvate conversion to lactate
• B. Increased fatty acid oxidation
• C. Decreased glycolysis
• D. Decreased lactate production

Answer: (A)

When energy demand is high during sustained exercise, glycolysis accelerates to supply ATP quickly. Even with oxygen present, the mitochondria may not oxidize NADH fast enough to keep up with the rapid production of NADH in glycolysis. To keep glycolysis going, pyruvate is converted to lactate by lactate dehydrogenase, which regenerates NAD+ needed for the glycolytic step that uses glyceraldehyde-3-phosphate dehydrogenase. This shift allows continued ATP production but results in lactate (lactic acid) accumulating in the blood. Fatty acid oxidation would use fats instead of producing much lactate, decreased glycolysis would reduce lactate production, and decreased lactate production wouldn’t explain accumulation.

When energy demand is high during sustained exercise, glycolysis accelerates to supply ATP quickly. Even with oxygen present, the mitochondria may not oxidize NADH fast enough to keep up with the rapid production of NADH in glycolysis. To keep glycolysis going, pyruvate is converted to lactate by lactate dehydrogenase, which regenerates NAD+ needed for the glycolytic step that uses glyceraldehyde-3-phosphate dehydrogenase. This shift allows continued ATP production but results in lactate (lactic acid) accumulating in the blood.

Fatty acid oxidation would use fats instead of producing much lactate, decreased glycolysis would reduce lactate production, and decreased lactate production wouldn’t explain accumulation.