# Describe what happens in the muscles during vigorous exercise when the body cannot supply enough oxygen, and explain why a person continues to breathe heavily for several minutes after the exercise stops.

> AQA GCSE Biology (8461) — 4.4.2 Respiration · Describe · 4 marks

## Mark scheme (4 marks)

1. Anaerobic respiration occurs in the muscles during vigorous exercise
2. Lactic acid is produced / builds up in the muscles
3. After exercise, extra oxygen is needed to remove / react with the accumulated lactic acid
4. This extra oxygen required is called the oxygen debt

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