Which tissue experiences lactic acid buildup during intense exercise?

• A. Liver tissue
• B. Brain tissue
• C. Muscle tissue
• D. Heart tissue

Answer: (C)

When exercise is very intense, oxygen delivery to muscles can’t keep up with demand, so muscle cells switch to anaerobic glycolysis. In this pathway, glucose is converted to pyruvate, and pyruvate is rapidly turned into lactate to regenerate NAD+, allowing glycolysis to continue. This causes lactate to accumulate in the muscle tissue, especially in fast-twitch fibers that rely more on anaerobic metabolism. The liver can take up lactate and convert it back to glucose (Cori cycle), so it isn’t the primary site of buildup during the bout. The brain mainly uses glucose, and the heart relies on aerobic metabolism and can oxidize lactate as fuel, so they don’t experience the same lactate buildup as working muscles. Therefore, muscle tissue is the tissue that experiences lactic acid buildup during intense exercise.