PE5: Cardiac Output, Stroke Volume & Heart Rate
The relationship between cardiac output, stroke volume and heart rate, anticipatory rise, and heart rate response to exercise.
💓 Key Definitions
Heart Rate (HR): The number of times the heart beats per minute. Measured in beats per minute (bpm).
Stroke Volume (SV): The volume of blood pumped out of the left ventricle per heartbeat. Measured in millilitres per beat (ml/beat).
Cardiac Output (CO): The total volume of blood pumped out of the left ventricle per minute. Measured in litres per minute (l/min).
Key Equation:
Cardiac Output = Stroke Volume × Heart Rate
CO = SV × HR
Example at rest: CO = 70 ml/beat × 72 bpm = 5,040 ml/min ≈ 5 l/min
Cardiac Output = Stroke Volume × Heart Rate
CO = SV × HR
Example at rest: CO = 70 ml/beat × 72 bpm = 5,040 ml/min ≈ 5 l/min
📊 Resting vs Exercising Values
| Variable | Resting Value (average adult) | Maximal Exercise Value |
|---|---|---|
| Heart Rate | 60-72 bpm | Up to 200+ bpm (max HR ≈ 220 - age) |
| Stroke Volume | 60-80 ml/beat | 120-160 ml/beat (untrained); up to 200 ml/beat (elite endurance athlete) |
| Cardiac Output | 5 l/min | 20-30 l/min (untrained); up to 40 l/min (elite endurance athlete) |
Calculating Cardiac Output
At rest: SV = 70 ml/beat, HR = 72 bpm
CO = 70 × 72 = 5,040 ml/min ≈ 5.0 l/min
During maximal exercise: SV = 150 ml/beat, HR = 190 bpm
CO = 150 × 190 = 28,500 ml/min ≈ 28.5 l/min
Elite endurance athlete at rest: SV = 110 ml/beat, HR = 40 bpm
CO = 110 × 40 = 4,400 ml/min ≈ 4.4 l/min
📈 Anticipatory Rise
Definition: An anticipatory rise is an increase in heart rate before exercise begins. It is caused by the release of the hormone adrenaline (epinephrine) from the adrenal glands in response to the excitement or stress of the upcoming activity.
- Heart rate can rise by 15-20 bpm above resting levels before exercise even starts
- This prepares the body for exercise by increasing blood flow to working muscles
- It is an emotional response, not a physical one - triggered by thinking about or preparing for activity
- More likely to occur in competitive or high-pressure situations (e.g. before a race)
Anticipatory Rise in Sport
A 100m sprinter in the blocks may have a heart rate of 120 bpm before the race has even started. The release of adrenaline causes the SA node to fire faster, increasing heart rate. This means oxygen and glucose are already being delivered to the muscles at an increased rate, giving the athlete a faster start.
📉 Heart Rate Response to Exercise and Recovery
During exercise: Heart rate increases rapidly at the start (due to anticipatory rise and the immediate demand for oxygen). It then increases more gradually until it reaches a steady state - the point where the heart rate meets the demands of the exercise. If exercise intensity increases further, heart rate continues to rise.
During recovery: After exercise stops, heart rate decreases. Initially, there is a rapid decrease in heart rate (the first 1-3 minutes) as the parasympathetic nervous system reduces the heart rate. This is followed by a gradual decrease back towards resting levels. Full recovery may take 30-60 minutes depending on fitness level and exercise intensity.
Interpreting Heart Rate Graphs
- At rest: Flat line at resting HR (60-72 bpm)
- Pre-exercise: Sharp rise due to anticipatory rise (adrenaline)
- Start of exercise: Rapid increase as the body responds to the demand
- During steady-state exercise: Plateau at a level that meets the exercise demands
- End of exercise: Rapid initial decrease, then gradual return to resting
Comparing Trained vs Untrained Recovery
A fitter person recovers faster after exercise because:
- Their stronger heart pumps more blood per beat (higher stroke volume)
- Their parasympathetic nervous system is more efficient at lowering heart rate
- Lactic acid is removed more quickly
- An elite athlete's heart rate may return to resting levels in 5-10 minutes
- An untrained person's heart rate may take 30-60 minutes to fully recover
🏃 Bradycardia in Trained Athletes
Bradycardia: A resting heart rate below 60 bpm. In trained endurance athletes, it is a positive adaptation - not a medical condition.
Endurance-trained athletes often have resting heart rates of 40-50 bpm. This occurs because:
- Regular aerobic training causes cardiac hypertrophy - the left ventricle grows larger and stronger
- A larger, stronger left ventricle pumps more blood per beat (increased stroke volume)
- Because each beat pumps more blood, the heart needs to beat fewer times per minute to maintain the same cardiac output at rest
- CO = SV × HR still applies: if SV increases, HR can decrease while maintaining the same CO
| Variable | Untrained Person | Trained Endurance Athlete |
|---|---|---|
| Resting HR | 60-72 bpm | 40-50 bpm |
| Resting SV | 70 ml/beat | 100-120 ml/beat |
| Resting CO | ~5 l/min | ~5 l/min |
| Max CO | 20-25 l/min | 35-40 l/min |
Bradycardia Calculation
A trained cyclist has a resting HR of 45 bpm and a resting SV of 110 ml/beat.
CO = 110 × 45 = 4,950 ml/min ≈ 5.0 l/min
This is the same cardiac output as an untrained person (70 × 72 = 5,040 ml/min), but achieved with fewer beats. The heart is working more efficiently.
🧠 Regulation of Heart Rate
The SA Node (Sinoatrial Node): The heart's natural pacemaker, located in the right atrium. It generates electrical impulses that control the heart rate.
- Sympathetic nervous system: Speeds up heart rate (fight or flight response; released during exercise)
- Parasympathetic nervous system: Slows down heart rate (rest and digest; active during recovery)
- Adrenaline: Hormone released by adrenal glands; increases heart rate and force of contraction
- Chemoreceptors: Detect changes in blood CO₂ levels; if CO₂ rises, they signal the brain to increase heart rate
❓ Practice Questions
Q1: State the equation linking cardiac output, stroke volume and heart rate.
Q2: Calculate the cardiac output of an athlete with a stroke volume of 120 ml/beat and a heart rate of 170 bpm during exercise.
Q3: Explain what is meant by an anticipatory rise and why it occurs.
Q4: Explain why a trained endurance athlete has a lower resting heart rate than an untrained person, despite having the same cardiac output at rest.
Q5: Describe the heart rate response during recovery from exercise.
Q6: A marathon runner has a resting HR of 42 bpm and a resting SV of 115 ml/beat. Calculate their resting cardiac output.
✅ Answers
- Cardiac Output = Stroke Volume × Heart Rate (CO = SV × HR).
- CO = 120 ml/beat × 170 bpm = 20,400 ml/min = 20.4 l/min.
- An anticipatory rise is an increase in heart rate before exercise begins, caused by the release of adrenaline from the adrenal glands. It is an emotional/psychological response to the anticipation of exercise, preparing the body by increasing blood flow to working muscles before activity starts.
- Regular aerobic training causes cardiac hypertrophy - the left ventricle becomes larger and stronger. This increases stroke volume, so the heart can pump the same cardiac output with fewer beats per minute. The athlete maintains the same resting cardiac output (~5 l/min) but with a higher SV and lower HR.
- After exercise stops, heart rate decreases rapidly in the first 1-3 minutes (parasympathetic nervous system activation). Then it decreases gradually back towards resting levels over 30-60 minutes. A fitter person recovers faster than an untrained person.
- CO = 115 × 42 = 4,830 ml/min ≈ 4.8 l/min.
🎯 Exam Tips
- The equation CO = SV × HR is guaranteed to appear - memorise it and practise calculations
- Always show your working in calculation questions
- Convert ml to litres by dividing by 1000 when giving cardiac output in l/min
- Use the term "anticipatory rise" and "adrenaline" specifically - don't just say "heart rate goes up before exercise"
- When describing recovery, mention both the rapid and gradual phases
- Bradycardia in athletes is a positive adaptation, not a medical problem
⚠️ Common Errors
Watch Out!
Students often forget to convert units in calculations. Wrong: "CO = 70 × 72 = 5040 litres/min." Correct: "CO = 70 × 72 = 5,040 ml/min = 5.04 l/min."
Students often think bradycardia is always a medical condition. Wrong: "Bradycardia is a heart problem." Correct: "In trained athletes, bradycardia (resting HR below 60 bpm) is a positive adaptation resulting from increased stroke volume."
📝 Exam Technique
PE Exam Tips — Cardiac Output, Stroke Volume & Heart Rate:
1. For Cardiac Output, Stroke Volume & Heart Rate questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of Cardiac Output, Stroke Volume & Heart Rate to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
1. For Cardiac Output, Stroke Volume & Heart Rate questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of Cardiac Output, Stroke Volume & Heart Rate to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
⚠️ Common Errors
Watch Out!
Students often think lactic acid causes doms. Wrong: Lactic acid causes DOMS Correct: DOMS (delayed onset muscle soreness) is caused by micro-tears in muscle fibres, not lactic acid. Lactic acid is cleared within an hour of exercise.
Students often think veins always carry deoxygenated blood. Wrong: Veins always carry deoxygenated blood Correct: Pulmonary veins carry oxygenated blood from the lungs to the heart. It is arteries and veins relative to the heart that matters, not oxygenation.
Students often think the heart beats faster during exercise just because you need more oxygen. Wrong: The heart beats faster during exercise just because you need more oxygen Correct: Heart rate increases due to anticipatory rise (before exercise), increased CO2 in blood detected by chemoreceptors, and decreased vagal tone. It is a coordinated response, not just oxygen demand.
✍️ Model Answer
Full-Mark Response
6 marks: Explain how cardiac output, stroke volume & heart rate affects sporting performance.
Cardiac Output, Stroke Volume & Heart Rate has significant effects on sporting performance. [Key concept 1]: explain the mechanism with specific detail. [Key concept 2]: how this applies in a named sporting example. [Key concept 3]: the relationship between this topic and overall performance. A grade 9 answer uses precise anatomical/physiological terminology, specific sporting examples, and evaluates the relative importance of different factors.
Mark scheme: 2 marks per explained point with specific evidence, evaluation for top marks
📊 AO Deep Dive
Assessment Objective Analysis
GCSE PE tests four AOs: AO1 (Knowledge, 30%) — recall facts about Cardiac Output, Stroke Volume & Heart Rate including definitions, classifications and specific examples; AO2 (Application, 30%) — apply knowledge to sporting contexts and training scenarios; AO3 (Analysis and Evaluation, 25%) — analyse data (graphs, tables), evaluate training methods or strategies, and justify recommendations; AO4 (Practical, 15%) — demonstrate relevant skills. For grade 9, use precise terminology, support every point with named sporting examples, and evaluate rather than just describe. The difference between grade 5 and grade 9 is the quality of application and depth of evaluation.
📝 Exam Questions by Topic
🎬 Video Resources
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