The correct option is Lactic acid.
Explanation
Muscle fatigue is a physiological decline in the ability of a muscle to generate force. It occurs when metabolic byproducts accumulate during periods of high energy demand where oxygen supply is insufficient.
Detailed Analysis:
- Lactic Acid (Correct): During prolonged strenuous exercise, the body cannot supply oxygen to the muscles fast enough to maintain aerobic respiration. To continue generating ATP, muscle cells switch to anaerobic respiration. In this process, glucose is broken down into pyruvate, which is subsequently converted into lactic acid. The accumulation of lactic acid (and associated hydrogen ions) lowers the pH within muscle cells, inhibiting enzyme function and interfering with the contractile mechanism, which results in fatigue and pain.
- Uric Acid: This is a metabolic waste product resulting from the breakdown of purines. High levels of uric acid typically lead to gout (inflammation in joints) or kidney stones, not acute muscle fatigue.
- Citric Acid: This is a key intermediate in the Krebs cycle (Citric Acid Cycle), which occurs during aerobic respiration. It is essential for energy production and does not accumulate to cause fatigue.
- Ammonia: Ammonia is produced during the deamination of amino acids. While it is toxic and can contribute to central nervous system fatigue, it is not the primary cause of local muscle fatigue compared to lactic acid accumulation.
Key Takeaway: Muscle fatigue during anaerobic exertion is primarily caused by the accumulation of lactic acid due to the incomplete oxidation of glucose in the absence of adequate oxygen.