Which statement is true about lactic acid buildup as a short-term effect?

• A. Contraction, lengthening, and relaxing at increased rate
• B. Increased muscle temperature
• C. More carbon dioxide produced
• D. Lactic acid builds up when oxygen supply cannot meet demand

Answer: (D)

When the muscles work hard and oxygen can’t keep up, the body switches to anaerobic glycolysis to keep producing ATP. This incomplete aerobic process leads to the accumulation of lactate in the muscles, creating an oxygen deficit short-term response. The buildup of lactate (often called lactic acid) happens precisely because oxygen supply cannot meet the demand, making that statement the correct one. The other ideas describe general effects of exercise or processes tied to oxygen when it’s available, not the specific short-term result of insufficient oxygen during intense effort.