# A sprinter finishes a 100 m race and immediately feels their leg muscles become stiff and sore. Explain how ATP is used during muscle contraction and describe what happens when ATP supply cannot meet the demand of contracting muscle fibres.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.2 Muscle contraction · Explain · 5 marks

> Skeletal muscles are made of muscle fibres containing overlapping actin and myosin filaments. Contraction requires a continuous supply of ATP. During intense, short-duration exercise such as sprinting, the muscles may not receive sufficient oxygen to produce all the ATP needed.

## Mark scheme (5 marks)

1. ATP provides energy for the myosin head to move / bind to actin and pull the actin filament
2. ATP is broken down (by ATPase) to ADP and inorganic phosphate, releasing energy
3. When oxygen supply is insufficient, anaerobic respiration occurs in the muscle cells
4. Anaerobic respiration produces lactic acid (lactate) in muscle cells
5. Accumulation of lactic acid causes muscle fatigue / pain / cramp, reducing the ability of muscles to contract

## Key terms

- [ATP](https://www.gradenine.co.uk/glossary/atp)
- [actin](https://www.gradenine.co.uk/glossary/actin)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-sprinter-finishes-a-100-m-c6537d3a) · Published by Druglandscape Ltd.