Blood samples were collected at the beginning of an aerobic exercise class and after thirty minutes of activity. Which post-exercise pattern is most consistent with the metabolic response?

• A. Normal lactic acid, low pyruvate
• B. Low lactic acid, elevated pyruvate
• C. Elevated lactic acid, low pyruvate
• D. Elevated lactic acid, elevated pyruvate

Answer: (D)

During sustained aerobic exercise, muscles ramp up glycolysis to meet energy needs, producing more pyruvate. Because oxygen is available, most of that pyruvate can be oxidized in the mitochondria, but the high rate of glycolysis also drives some pyruvate to be reduced to lactate to regenerate NAD+ and keep glycolysis running. As a result, both pyruvate and lactate rise in the blood after ongoing activity, reflecting increased glycolytic flux and continued oxidative metabolism. Therefore, elevated lactic acid and elevated pyruvate after 30 minutes best fits the metabolic response.