Final answer:
When muscle cells don't receive enough oxygen, they undergo anaerobic glycolysis, where pyruvic acid is converted into lactic acid, a substance that can lead to muscle fatigue when it accumulates.
Step-by-step explanation:
What Builds up in Muscles When Oxygen is Insufficient?
During exercise or situations where there is a lack of oxygen, muscle cells rely on a process called anaerobic glycolysis to produce energy.
In this scenario, instead of using oxygen to fully break down glucose into carbon dioxide and water during aerobic respiration, the cells convert pyruvic acid into lactic acid.
This process allows the recycling of the enzyme NAD+ from NADH, which is needed for glycolysis to continue.
Although this shift to anaerobic metabolism provides a rapid burst of energy, it is not sustainable for long periods and leads to a build-up of lactic acid, which may contribute to muscle fatigue as it accumulates.