How is lactic acid produced during high-intensity exercise?

• A. Aerobic metabolism of glucose
• B. Lipolysis
• C. Oxidative phosphorylation
• D. Anaerobic metabolism of glucose

Answer: (D)

When exercise is very intense, the muscles can’t get enough oxygen fast enough to meet the energy demand, so the body relies on anaerobic glycolysis to produce ATP quickly. Glucose is broken down to pyruvate through glycolysis, giving a small amount of ATP. With limited oxygen, pyruvate isn’t fed into the mitochondria for oxidative phosphorylation; instead, it is converted to lactate by lactate dehydrogenase, which also regenerates NAD+ needed to keep glycolysis going. This rapid production of lactate is the hallmark of anaerobic metabolism of glucose during high-intensity work. Aerobic metabolism and oxidative phosphorylation require oxygen and produce much more ATP without lactate, while lipolysis breaks down fats and isn’t the immediate source of lactate in these conditions.