Investigate and state the effect of physical activity on pulse rate.

Transport in Humans – Effect of Physical Activity on Pulse Rate

Learning Objectives (AO1, AO2, AO3)

• Explain how the structure of the human circulatory system enables the transport of nutrients, gases and waste.
• Investigate how the intensity and duration of physical activity affect pulse rate and cardiac output.
• Analyse experimental data, evaluate sources of error and relate findings to fitness and long‑term health.

Syllabus Context (IGCSE 0610 – Core)

Background Information

1. The Human Circulatory System

• Closed system of arteries, veins and capillaries that transports blood round the body.
• Heart acts as a muscular pump; valves ensure one‑way flow.
• Arterial blood is high‑pressure; venous blood returns at low pressure, aided by skeletal‑muscle pumps and one‑way valves.

2. The Heart – structure and cardiac cycle

• Four chambers: two atria (receive blood) and two ventricles (pump blood).
• Valves: tricuspid, mitral, pulmonary and aortic – prevent back‑flow.
• Systole: ventricles contract, ejecting blood into the arteries (produces the pressure wave we feel as a pulse).
• Diastole: ventricles relax and fill.
• Heart sounds (lub‑dub) correspond to valve closure; an ECG records the electrical activity that triggers each contraction.

3. Blood Vessels and the Pulse Wave

• Arteries – thick, elastic walls; high pressure; transmit the pulse wave.
• Veins – thin walls, contain valves, act as a blood reservoir and rely on muscle contractions to return blood to the heart.
• Capillaries – walls only one cell thick; site of exchange of O₂, CO₂, nutrients and waste.

4. Blood – components and function

• Red blood cells contain haemoglobin, which binds O₂ and transports it from lungs to tissues.
• Plasma carries nutrients, hormones and waste products; platelets and clotting factors prevent blood loss.
• During exercise the demand for O₂ rises, so the circulatory system must deliver more oxygen‑rich blood and remove CO₂ more rapidly.

5. Cardiac Output and its relationship to pulse

Cardiac output (Q) = Stroke volume (SV) × Heart rate (HR)

• Stroke volume – volume of blood ejected with each beat (≈70 mL at rest, can rise to 100 mL or more during vigorous exercise).
• Heart rate (HR) – beats per minute; measured as the pulse rate.
• During moderate‑to‑vigorous activity both SV and HR increase, allowing Q to rise to 5–6 times the resting value.

6. Regulation of Heart Rate (Homeostasis)

• Autonomic nervous system:
  • Sympathetic stimulation → ↑ HR and contractility (via norepinephrine).
  • Parasympathetic (vagal) stimulation → ↓ HR (via acetylcholine).
• Adrenaline (epinephrine) released from the adrenal medulla during exercise further raises HR and SV.
• Baroreceptor reflex detects changes in arterial pressure and adjusts HR and vessel diameter to maintain blood pressure – a classic negative‑feedback loop.

7. Link to Gas Exchange & Respiration

• Active muscles increase their metabolic rate → higher O₂ consumption and CO₂ production.
• Increased cardiac output delivers O₂‑rich blood faster and returns CO₂‑rich blood to the lungs for exhalation.
• Aerobic exercise (e.g., jogging) relies on continuous O₂ supply, whereas anaerobic bursts (e.g., sprinting) cause a rapid, short‑term rise in HR.

8. Homeostatic Control of Heart Rate

The combined action of the sympathetic and parasympathetic systems, together with hormonal (adrenaline) and baroreceptor inputs, provides a rapid, negative‑feedback mechanism that matches heart rate to the body’s metabolic needs.

Key Concepts

• Resting pulse rate – typical range for adolescents: 60–100 bpm.
• Exercise pulse rate – rises proportionally with intensity and duration.
• Recovery pulse – the rate at which HR returns toward resting level after exercise; a rapid fall indicates good cardiovascular fitness.
• Percentage change in pulse – $$\% \Delta P = \frac{P_{\text{immediate}}-P_{\text{rest}}}{P_{\text{rest}}}\times100$$
• Practical skills (AO3) – measuring pulse, using a stopwatch, recording data, calculating % change, plotting graphs, evaluating sources of error.

Hypothesis

Physical activity will increase pulse rate. The greater the intensity or duration of the activity, the larger the increase. A fitter individual will show a quicker return to resting pulse during the recovery phase.

Materials

• Stopwatch or digital timer
• Pulse‑counting device (digital heart‑rate monitor, manual pulse counter, or ruler for counting beats)
• Exercise equipment – e.g., skipping rope, stationary bike, or a marked 200 m track
• Data‑recording sheet (table & graph paper or spreadsheet)
• Pen, pencil and calculator
• First‑aid kit (for safety)

Method (Step‑by‑Step)

1. Allow the participant to sit quietly for 5 minutes. Measure the resting pulse:
   • Place two fingers on the radial artery.
   • Count beats for 30 seconds and multiply by 2. Record as P_rest (bpm).
2. Choose an activity level and note its intensity or duration (e.g., “moderate – 4 min skipping at a cadence of ~120 beats min⁻¹”).
3. Start the activity and the timer simultaneously.
4. Immediately on completion, measure the pulse as in step 1 and record as P_immediate.
5. Allow the participant to rest for 1 minute, then measure the pulse again and record as P_recovery.
6. Repeat steps 2‑5 for at least three different intensities (low, moderate, high). Optional: add a “maximum effort” level.
7. For each activity calculate the percentage increase: $$\% \Delta P = \frac{P_{\text{immediate}}-P_{\text{rest}}}{P_{\text{rest}}}\times100$$
8. Plot a graph of P_immediate (y‑axis) against activity intensity or duration (x‑axis) to visualise the trend.

Data Collection Table

Analysis

• Trend identification – Compare P_immediate with P_rest for each intensity. A clear upward trend supports the hypothesis.
• Recovery assessment – Calculate P_recovery – P_rest. A small difference after 1 min indicates good fitness; a large difference suggests lower cardiovascular efficiency.
• Graphical representation – Plot HR (y‑axis) against intensity/duration (x‑axis). The slope provides a visual measure of the cardiovascular response.
• Statistical treatment (optional) – If several pupils repeat the experiment, compute the mean % increase and standard deviation for each intensity to assess repeatability.
• Sources of error (AO3)
  • Delay between stopping the activity and starting the pulse count.
  • Inconsistent counting period (e.g., 15 s instead of 30 s).
  • External influences – caffeine, stress, ambient temperature.
  • Manual counting vs. digital monitor – accuracy differences.
  • Individual variation in fitness level.

Conclusion

Summarise whether the experimental data support the hypothesis that pulse rate rises with increasing physical activity. Explain the physiological basis – sympathetic stimulation, increased stroke volume, higher cardiac output – and relate the speed of recovery to cardiovascular fitness. Discuss any anomalies and suggest how the experiment could be refined.

Safety and Ethical Considerations

• Confirm that participants are medically cleared for moderate exercise.
• Include a brief warm‑up (3 min gentle walking) and a cool‑down (slow stretching) to reduce injury risk.
• Monitor for dizziness, shortness of breath or chest pain; stop the activity immediately if any occur.
• Obtain informed consent from pupils (or parents/guardians for younger students) before the practical.
• Maintain privacy when recording personal data such as resting pulse.

Extension Activities

• Aerobic vs. anaerobic exercise – Compare pulse response after a 5‑min jog (aerobic) with a 30‑s sprint (anaerobic).
• Recovery time measurement – Record the exact time taken for the pulse to return to within 5 bpm of the resting value; use this as a quantitative fitness indicator.
• Influence of age, gender and BMI – Collect data from a mixed group and analyse how these variables affect resting and exercise pulse rates.
• Coronary heart disease (extended syllabus) – Discuss how a consistently high resting pulse can be a risk factor for CHD. Relate students’ own data to lifestyle choices (diet, regular exercise) that reduce long‑term risk.
• Alternative monitoring techniques – Use a simple ECG or a finger‑pulse oximeter to compare with manual pulse counts.