What substance accumulates in muscle during anaerobic respiration, potentially leading to fatigue?

During anaerobic respiration, the primary pathway for energy production in the absence of sufficient oxygen is through the breakdown of glucose. However, this process leads to the accumulation of lactic acid as a byproduct when pyruvate, produced from glucose, is converted anaerobically.

Lactic acid is formed when the body shifts to anaerobic metabolism, especially during intense physical activity when the oxygen supply is limited. Accumulation of lactic acid in the muscles is associated with a decrease in pH, which contributes to the sensation of muscle fatigue and discomfort. This is why lactic acid is specifically noted as causing fatigue during bouts of activity that exceed the oxygen supply available for aerobic respiration.

Glucose is not the correct answer as it is the starting substrate for energy production, not a waste product. Carbon dioxide is another byproduct of cellular respiration, but its accumulation is more relevant to aerobic processes. Creatine, while involved in energy metabolism, does not lead to fatigue through accumulation like lactic acid does. The body can manage creatine levels differently compared to lactic acid, which has a more direct impact during anaerobic activities.