Explain why athletes who sprint a 100 m race continue to breathe rapidly for several minutes after they cross the finish line, even though the race is over.

Pearson Edexcel International GCSE Biology (4BI1) — 2.7 Respiration · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

During a 100 m sprint, muscle cells respire anaerobically as well as aerobically. After the race, the athletes stop running but their breathing rate remains elevated for some time.

Model answer (4 marks)

During the sprint the muscles use anaerobic glycolysis, producing lactic acid.
After the race the body must oxidise this lactic acid, which requires extra oxygen – the oxygen debt.
To repay the debt the body increases ventilation, allowing more oxygen to be taken in and delivered to tissues.
Thus breathing remains rapid for several minutes after the finish line.

Examiner tips

  • Use the term "oxygen debt" and link it to lactic acid oxidation.
  • Show the cause (anaerobic glycolysis) and effect (increased ventilation).
  • Mention that the extra oxygen is needed to repay the debt.

Common mistakes

  • Failing to mention lactic acid or oxygen debt.
  • Using vague phrases like "more oxygen" without explaining why it is needed.
  • Not linking the rapid breathing to the repayment of the oxygen debt.

Mark scheme (4 marks)

  1. During the sprint, muscles respired anaerobically and produced lactic acid
  2. After the race, extra oxygen is needed to break down / oxidise the lactic acid
  3. This extra oxygen required is called the oxygen debt
  4. Rapid breathing allows more oxygen to be taken in / delivered to tissues to repay the oxygen debt

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