A student is investigating the effect of regular aerobic exercise on the cardiovascular system. The student finds that trained athletes have a lower resting heart rate than non-athletes, yet both groups deliver an adequate supply of oxygen to body tissues at rest. Explain how the heart of a trained athlete is able to maintain adequate oxygen delivery to tissues despite having a lower resting heart rate.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Regular aerobic exercise causes long-term adaptations to the heart. Trained athletes typically have a resting heart rate of around 40–50 beats per minute, compared to approximately 70 beats per minute in a non-athlete.
Model answer (5 marks)
The heart delivers oxygen by pumping blood that contains haemoglobin.
1. Cardiac output (CO) = heart rate (HR) × stroke volume (SV).
2. In athletes HR is lower (≈40–50 bpm) but SV is higher because the myocardium is stronger and the ventricles are larger.
3. The increased SV compensates for the lower HR, giving the same or greater CO as a non‑athlete.
4. Thus the same or greater volume of oxygen‑rich blood reaches tissues each minute, maintaining adequate oxygen delivery at rest.
1. Cardiac output (CO) = heart rate (HR) × stroke volume (SV).
2. In athletes HR is lower (≈40–50 bpm) but SV is higher because the myocardium is stronger and the ventricles are larger.
3. The increased SV compensates for the lower HR, giving the same or greater CO as a non‑athlete.
4. Thus the same or greater volume of oxygen‑rich blood reaches tissues each minute, maintaining adequate oxygen delivery at rest.
Examiner tips
- State CO = HR × SV and explain the relationship.
- Show that athletes have a larger SV due to a stronger, thicker heart.
- Link the larger SV to the same or higher CO despite lower HR.
- Use the term ‘oxygen delivery’ or ‘oxygen supply’ to match the mark scheme.
Common mistakes
- Confusing heart rate with cardiac output.
- Failing to mention the increased stroke volume.
- Using the wrong units or not showing the CO equation.
Mark scheme (5 marks)
- The heart pumps blood containing oxygen to the tissues / oxygen is carried in the blood to body cells
- Cardiac output = heart rate × stroke volume (concept stated or implied)
- The athlete's heart has a greater stroke volume (more blood pumped per beat) than a non-athlete's heart
- The greater stroke volume compensates for the lower heart rate, so the same / adequate volume of blood (and therefore oxygen) is delivered per minute
- Regular exercise causes the heart muscle (myocardium / cardiac muscle) to become stronger / thicker / the heart to become larger, enabling the greater stroke volume
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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