- In conditions where oxygen supply to muscle cells is limited, such as during intense exercise, anaerobic glycolysis becomes the primary pathway for energy production.
- Under these anaerobic conditions, pyruvic acid, the end product of glycolysis, cannot enter the mitochondria for aerobic respiration.
- Instead, it is converted into lactic acid (or lactate) by the enzyme lactate dehydrogenase.
- This conversion allows glycolysis to continue by regenerating NAD⁺, which is essential for the breakdown of glucose to produce ATP.

- The accumulation of lactic acid in muscle cells leads to temporary muscle fatigue and soreness.
- Once oxygen levels are restored, lactic acid is transported to the liver where it can be converted back to glucose through the Cori cycle.

Other options like acetoacetic acid and citric acid are not involved in anaerobic glycolysis:
- Acetoacetic acid is a ketone body produced primarily in the liver during prolonged fasting or diabetes.
- Citric acid is an intermediate in the aerobic citric acid cycle (Krebs cycle) and is formed during aerobic metabolism, not anaerobic glycolysis.

Therefore, the correct metabolite that accumulates as a result of anaerobic glycolysis in muscle cells is lactic acid.

Reference: Lehninger Principles of Biochemistry, 7th Edition, Chapter 15 / Pages 612-615