Which reaction is the primary cause of metabolic acidosis during high-intensity exercise?

Which reaction is the primary cause of metabolic acidosis during high-intensity exercise?

• A. ATP = ADP + Pi + H+
• B. Pyruvate + NADH = Lactate + NAD+
• C. ADP + Creatine phosphate = ATP + Creatine
• D. Fructose-6-phosphate = Fructose-1,6-biphosphate

Answer: (A)

During high-intensity exercise, ATP turnover skyrockets, so ATP is rapidly hydrolyzed: ATP + H2O → ADP + Pi + H+. This reaction directly releases a proton into the muscle, contributing immediately to a drop in pH and metabolic acidosis. While lactate production accompanies anaerobic glycolysis, the lactate dehydrogenase step actually consumes a proton (pyruvate + NADH + H+ → lactate + NAD+), so it does not drive acidosis. The phosphocreatine system regenerates ATP without releasing H+, and the glycolytic step that uses ATP (fructose-6-phosphate to fructose-1,6-bisphosphate) consumes ATP but does not itself release a proton. Therefore, the direct proton release from ATP hydrolysis is the primary source of the H+ load that causes metabolic acidosis during intense effort.

During high-intensity exercise, ATP turnover skyrockets, so ATP is rapidly hydrolyzed: ATP + H2O → ADP + Pi + H+. This reaction directly releases a proton into the muscle, contributing immediately to a drop in pH and metabolic acidosis. While lactate production accompanies anaerobic glycolysis, the lactate dehydrogenase step actually consumes a proton (pyruvate + NADH + H+ → lactate + NAD+), so it does not drive acidosis. The phosphocreatine system regenerates ATP without releasing H+, and the glycolytic step that uses ATP (fructose-6-phosphate to fructose-1,6-bisphosphate) consumes ATP but does not itself release a proton. Therefore, the direct proton release from ATP hydrolysis is the primary source of the H+ load that causes metabolic acidosis during intense effort.