Final answer:
When muscle cells are depleted of oxygen, they switch to anaerobic metabolism, producing lactic acid and a minimal amount of ATP via glycolysis. This can lead to muscle fatigue but is essential for short bursts of intense activity. Subsequently, the body incurs an oxygen debt that must be resolved by increased oxygen intake.
Step-by-step explanation:
When muscle cells run out of oxygen, they cannot produce ATP through aerobic respiration and instead rely on an anaerobic process known as glycolysis. This results in the production of lactic acid, which may contribute to muscle fatigue. During glycolysis, a small amount of ATP is generated, which is crucial for short bursts of high-intensity muscle activity. However, the efficiency of ATP production is much lower than when oxygen is plentiful. Following intense activity, an oxygen debt is accrued, requiring increased oxygen intake to restore ATP levels, convert lactic acid back to pyruvic acid, and ultimately alleviate muscle fatigue.