By the end of this lesson
- Explain heart-rate change during exercise.
- Explain adrenaline effects on the heart.
- Use cardiac-output relationships without diagnosing fitness.
BIG QUESTION
How can the heart increase delivery within seconds of exercise or danger?
Nervous and hormonal signals raise rate and force, increasing blood flow to active tissues.
Exercise raises metabolic demand
Contracting muscles use ATP faster, increasing oxygen and glucose demand and carbon-dioxide/heat production.
Heart rate and stroke volume rise, increasing cardiac outputThe volume of blood pumped by the heart per minute: heart rate multiplied by stroke volume. and helping maintain exchange gradients.
Adrenaline prepares rapid action
Adrenaline binds receptors in cardiac tissue, increasing pacemaker rate and contraction force. It supports increased delivery during exercise or a fight-or-flight response.
The response is regulated and varies with intensity, training, temperature, emotion and health.
Recovery restores baseline
Heart rate remains elevated briefly to support carbon-dioxide removal, temperature control and restoration of energy-related stores.
Classroom pulse data show physiological response only; they must be voluntary, device-local or temporary, and not used to diagnose or publicly rank pupils.
Rest, exercise and adrenaline
Several variables contribute to delivery.
| Condition | Heart response | Purpose |
|---|---|---|
| Rest | Lower rate/output. | Matches baseline demand. |
| Exercise | Rate and stroke volume rise. | More oxygen/nutrients; faster waste/heat removal. |
| Adrenaline | Rate and contraction force rise. | Prepares rapid action. |
| Recovery | Gradual return toward baseline. | Supports restoration and heat/waste removal. |
Language that earns precision
- heart rate
- Number of heart beats per minute.
- stroke volume
- Volume pumped by one ventricle per beat.
- cardiac output
- Blood volume pumped per minute: heart rate × stroke volume.
- adrenaline
- Hormone that prepares the body for rapid action.
Common misconceptions
Claim: Heart rate rises only because muscles need oxygen.
Correction: Delivery of glucose and removal of carbon dioxide/heat also matter.
Claim: Adrenaline is released only during fear.
Correction: It can contribute during exercise and other stresses.
Claim: A single recovery time measures fitness perfectly.
Correction: Many variables affect it; classroom data are not diagnostic.
Match the answer to the command word
Demand → rate/output → delivery/removal.
cardiac output = heart rate × stroke volume; include volume per minute.
Recall, apply, then justify
Explain why heart rate increases during exercise.
Hint
Start with muscle ATP demand.
Suggested marking points
- Muscle contraction increases ATP demand.
- Aerobic respiration requires more oxygen/glucose.
- More carbon dioxide/heat must be removed.
- Higher heart rate increases cardiac output and transport.
A heart rate is 120 beats min⁻¹ and stroke volume is 80 cm³. Calculate cardiac output.
Hint
Multiply and state per minute.
Suggested marking points
- 120 × 80.
- Cardiac output = 9600 cm³ min⁻¹ (9.6 dm³ min⁻¹).
Explain why cardiac output can rise even if heart-rate increase is modest.
Planning hint
Use both factors in the equation.
What a strong design includes
- Cardiac output equals heart rate multiplied by stroke volume.
- Exercise increases venous return and contraction strength.
- Stroke volume can therefore increase.
- A larger volume is ejected per beat.
- Output can rise substantially without a proportionally large rate increase.