# A mountaineer climbing at high altitude notices that their muscles become fatigued and painful much more quickly than when climbing at sea level. Explain why the mountaineer's muscles fatigue more quickly at high altitude.

> WJEC GCSE Biology (Wales) — 1.2.1 Aerobic and anaerobic respiration · Explain · 4 marks

> At high altitude, the concentration of oxygen in the air is much lower than at sea level.

## Mark scheme (4 marks)

1. At high altitude there is less oxygen available to the muscles
2. The muscles switch to anaerobic respiration (because aerobic respiration cannot meet the energy demand)
3. Anaerobic respiration produces lactic acid in the muscles
4. The build-up of lactic acid causes muscle fatigue / pain

## Key terms

- [fatigue](https://www.gradenine.co.uk/glossary/fatigue)

## Related

- [Revision notes for WJEC GCSE Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-mountaineer-climbing-at-high-altitude-b375c936) · Published by Druglandscape Ltd.