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This lesson covers heart rate, stroke volume, and cardiac output as required by the OCR GCSE PE specification (J587). You need to understand the definitions of each term, know the key equation (Q = SV x HR), and be able to interpret and apply heart rate data in sporting contexts.
| Term | Definition | Unit |
|---|---|---|
| Heart rate (HR) | The number of times the heart beats per minute | Beats per minute (bpm) |
| Stroke volume (SV) | The volume of blood pumped out of the left ventricle with each beat | Millilitres per beat (ml/beat) |
| Cardiac output (Q) | The total volume of blood pumped out of the left ventricle per minute | Litres per minute (l/min) or ml/min |
Heart rate is the number of times the heart beats per minute. It is the simplest measure of how hard the heart is working.
During exercise, heart rate increases because:
After exercise, heart rate gradually returns to its resting level. The time this takes is called the recovery time. A fitter person recovers faster — their heart rate returns to resting levels more quickly.
Exam Tip: OCR may ask you to interpret a heart rate graph showing heart rate before, during, and after exercise. Be prepared to identify: (1) the resting heart rate, (2) the increase during exercise, (3) the peak heart rate, and (4) the recovery time.
Stroke volume is the volume of blood ejected from the left ventricle with each heartbeat.
| Condition | Typical Stroke Volume |
|---|---|
| At rest (untrained person) | Approximately 70 ml per beat |
| At rest (trained athlete) | Approximately 100+ ml per beat |
| During maximal exercise | Can increase to 150-200+ ml per beat |
Regular training causes the heart muscle to grow larger and stronger (a process called cardiac hypertrophy). A larger, stronger heart:
Cardiac output is the total volume of blood pumped by the left ventricle per minute. It tells you how much blood the heart is delivering to the body in total.
Or: Q = SV x HR
| Condition | HR (bpm) | SV (ml) | Q (ml/min) | Q (l/min) |
|---|---|---|---|---|
| At rest | 70 | 70 | 4,900 | ~5 |
| During exercise | 150 | 120 | 18,000 | 18 |
| Maximal exercise (athlete) | 190 | 170 | 32,300 | ~32 |
Exam Tip: You MUST be able to use the equation Q = SV x HR in calculations. If given two values, you must be able to calculate the third. For example: if HR = 140 bpm and SV = 100 ml, then Q = 140 x 100 = 14,000 ml/min (or 14 l/min).
A resting athlete has a heart rate of 55 bpm and a stroke volume of 95 ml. Calculate their cardiac output.
Q = SV x HR = 95 x 55 = 5,225 ml/min (or 5.225 l/min)
During exercise, a person's cardiac output is 20,000 ml/min and their heart rate is 160 bpm. Calculate their stroke volume.
SV = Q ÷ HR = 20,000 ÷ 160 = 125 ml per beat
An untrained person has a resting stroke volume of 70 ml and a resting heart rate of 72 bpm. After six months of training, their stroke volume increases to 90 ml and their resting heart rate drops to 56 bpm. Calculate the cardiac output before and after training.
Notice that the cardiac output at rest is approximately the same — the body still needs the same amount of blood at rest. However, the trained heart achieves this with fewer, more powerful beats.
graph LR
A["Exercise begins"] --> B["Muscles demand<br>more O₂"]
B --> C["Heart rate increases"]
B --> D["Stroke volume increases"]
C --> E["Cardiac output<br>increases"]
D --> E
style A fill:#4a90d9,color:#fff
style E fill:#27ae60,color:#fff
| Variable | At Rest | During Exercise | Explanation |
|---|---|---|---|
| Heart rate | ~70 bpm | Up to 200+ bpm | Increases to pump blood faster |
| Stroke volume | ~70 ml | Up to 170+ ml | Increases because more blood returns to the heart |
| Cardiac output | ~5 l/min | Up to 30+ l/min | Increases because both HR and SV increase |
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