# During a sprint race, a runner's muscles switch from aerobic to anaerobic respiration. Describe what happens to the lactic acid that accumulates in the muscles during and after the race.

> Cambridge International IGCSE Biology (0610) — 12.1 Respiration · Describe · 4 marks

## Mark scheme (4 marks)

1. Lactic acid builds up / accumulates in the muscles during anaerobic respiration
2. Lactic acid causes muscle fatigue / cramp
3. Lactic acid is transported to the liver
4. In the liver, lactic acid is oxidised / broken down / converted to glucose using oxygen (repaying the oxygen debt)

## Key terms

- [lactic acid](https://www.gradenine.co.uk/glossary/lactic-acid)
- [anaerobic respiration](https://www.gradenine.co.uk/glossary/anaerobic-respiration)

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Source: [GradeNine](https://www.gradenine.co.uk/q/during-a-sprint-race-a-runner-s-52a3717e) · Published by Druglandscape Ltd.