The specification says: Investigate and describe the effect of physical activity on the heart rate
Aim
To investigate how different levels of physical activity affect the heart rate, measured as the pulse rate in beats per minute.
Background
The activity of the heart can be monitored by an ECG, by the pulse rate and by listening to the sounds of the valves closing. The pulse rate is the number of times the artery wall expands each minute as blood is pumped through it, and it is the same as the heart rate. It can be felt at the wrist or the neck.
Supplement: during physical activity the muscles respire faster, so they need more oxygen and glucose and produce more carbon dioxide. The heart rate increases so that blood flows faster, bringing oxygen and glucose to the muscles faster and removing carbon dioxide faster.
After exercise the heart rate falls back to the resting rate. The time this takes is the recovery time. The harder the exercise, the higher the heart rate and the longer the recovery.
Hypothesis
The harder the physical activity, the higher the heart rate and the longer the time taken to return to the resting rate, because the muscles need more oxygen and glucose.
Variables
| Independent | The level of physical activity (rest, walking, jogging, running on the spot), each for 2 minutes |
|---|---|
| Dependent | Heart rate (pulse rate) in beats per min, found from the number of beats in 15 s, and the recovery time in min |
| Control |
|
Equipment
- Stop-clock or stopwatch reading to 1 s or better
- A flat, clear, dry area to exercise in
- Chair
- Results table and pencil
Risk assessment
| Hazard | Risk | Precaution |
|---|---|---|
| Physical exercise | Dizziness, breathlessness or muscle strain, especially for a person with a heart or breathing condition. | Do not take part if you have a medical condition that affects exercise. Stop at once if you feel dizzy, faint or unwell. |
| Running on the spot | Slipping or tripping. | Exercise on a clear, dry floor away from furniture and wear suitable footwear. |
Method
- Sit on a chair and rest for 5 minutes.
- Find your pulse with two fingers on the inside of your wrist, below the thumb. Do not use your thumb.
- Start the stop-clock and count the number of beats in 15 s. Record the number of beats. This is the resting pulse.
- Walk on the spot for 2 minutes.
- Sit down at once, find your pulse and count the beats in 15 s, then record the number of beats.
- Count the beats in 15 s again at the start of every minute until the count is back to the resting value. Record the recovery time to the nearest minute.
- Rest until your pulse is back to the resting value.
- Repeat steps 4 to 7 for jogging on the spot, then for running on the spot, each for 2 minutes. Keep everything else the same.
- Repeat the whole investigation a second time and record the second set of readings.
- Calculate the mean number of beats in 15 s for each activity.
- Calculate the heart rate in beats per min using: heart rate = mean number of beats in 15 s × 4.
- Present the results as a bar chart of heart rate against activity.
Results
Fill this table in as you go. Print the PDF for a copy to write on.
| activity | beats in 15 s: 1 | beats in 15 s: 2 | mean beats in 15 s | heart rate / beats per min | recovery time / min |
|---|---|---|---|---|---|
| rest | – | ||||
| walking on the spot | |||||
| jogging on the spot | |||||
| running on the spot |
Drawing the graph
A bar chart with the activity (rest, walking, jogging, running) on the x-axis and heart rate / beats per min on the y-axis. The activities are separate categories, so draw bars of equal width that do not touch. Choose a scale so that more than half of the grid is used, label both axes with the quantity and unit, and draw the bars with a ruler.
Example results and answersPractice data, conclusion, errors and 10 exam questions (26 marks) with mark schemes
Example results
| activity | beats in 15 s: 1 | beats in 15 s: 2 | mean beats in 15 s | heart rate / beats per min | recovery time / min |
|---|---|---|---|---|---|
| rest | 19 | 20 | 19.5 | 78 | – |
| walking on the spot | 25 | 23 | 24.0 | 96 | 1 |
| jogging on the spot | 31 | 33 | 32.0 | 128 | 3 |
| running on the spot | 38 | 36 | 37.0 | 148 | 6 |
Conclusion
The heart rate increased as the physical activity became harder, from 78 beats per min at rest to 148 beats per min after running on the spot. The recovery time also became longer, from 1 min after walking to 6 min after running. This supports the hypothesis. Supplement: the muscles respire faster during harder activity, so they need more oxygen and glucose and produce more carbon dioxide. The heart beats faster so that the blood delivers oxygen and glucose to the muscles faster and removes carbon dioxide faster. After hard exercise the heart rate stays high for a while, to carry lactic acid from the muscles to the liver.
Errors and improvements
| Error | Effect on the results | Improvement |
|---|---|---|
| The pulse is counted for only 15 s and then multiplied by 4. | Missing one beat changes the heart rate by 4 beats per min, so the readings are not very precise. | Count for 30 s or 60 s, or use a pulse sensor or heart rate monitor. |
| The pulse falls quickly after exercise, so the count starts late. | The heart rate recorded is too low. | Start counting immediately after stopping, and use a pulse monitor that records during the exercise. |
| The level of exercise is judged by eye and is not the same each time. | The activity is not a fair test, so the heart rate readings vary. | Use a fixed exercise such as step-ups on a step of fixed height at a fixed rate with a metronome. |
| Only one person is used and each activity is done once or twice. | The results may not be typical, and one reading may be anomalous. | Repeat more times and use several people of the same age and fitness, then calculate a mean. |
| The person does not fully recover before the next activity. | The next activity starts from a higher heart rate, so its heart rate is too high. | Wait until the pulse is back to the resting value, for example check that the count is the same as at the start. |
Exam questions
10 questions, 26 marks. Write your answers on paper, then open each mark scheme.
Question 1
A student counts 29 beats in 15 s. Calculate the heart rate in beats per min.
Show mark scheme for question 1
- 29 × 4 (1)
- 116 beats per min (1) unit required; allow bpm
Question 2
A student investigates the effect of physical activity on heart rate. (a) State the independent variable. [1] (b) State the dependent variable. [1] (c) State one variable that must be kept constant. [1]
Show mark scheme for question 2
- (a) the level / type / intensity of physical activity (1)
- (b) heart rate / pulse rate (1) allow number of beats in 15 s
- (c) any one from: same person / same length of time for each activity / same time of day / same way of counting the pulse / same rest between activities (1)
Question 3
The student measures the resting pulse before the exercise, and waits until the pulse returns to the resting rate before the next activity. Explain why each of these is done.
Show mark scheme for question 3
- the resting rate is needed for comparison / to show the effect of the exercise (1)
- so that each activity starts from the same heart rate / so that the previous activity does not affect the result (1)
Question 4
The resting heart rate was 78 beats per min and the heart rate after running was 148 beats per min. Calculate the percentage increase in heart rate. Show your working.
Show mark scheme for question 4
- 148 − 78 = 70 (1)
- 70 ÷ 78 × 100 (1)
- 89.7% (1) allow 90% or 89.74%
Question 5
The table shows the results of a student's investigation. Describe the effect of the level of activity on the heart rate and on the recovery time.
| activity | heart rate / beats per min | recovery time / min |
|---|---|---|
| rest | 78 | – |
| walking | 96 | 1 |
| jogging | 128 | 3 |
| running | 148 | 6 |
Show mark scheme for question 5
- the harder the activity, the higher the heart rate (1)
- the harder the activity, the longer the recovery time (1)
- quotes paired data, e.g. heart rate rises from 78 at rest to 148 beats per min after running / recovery time from 1 min to 6 min (1)
Question 6
Supplement. Explain why the heart rate increases during physical activity.
Show mark scheme for question 6
- muscles respire faster / more (aerobic) respiration (1)
- more oxygen and glucose needed by the muscles / more carbon dioxide produced (1)
- blood flows faster so oxygen and glucose are delivered faster / carbon dioxide is removed faster (1)
- allow lactic acid removed faster (1)
- reject ‘to make energy’
- Max 3
Question 7
Describe two safety precautions for the person doing the exercise.
Show mark scheme for question 7
- do not take part if you have a heart or breathing condition / medical condition (1)
- stop if you feel dizzy / faint / unwell (1)
- exercise on a clear, dry floor away from furniture (1)
- Max 2
Question 8
Suggest three ways to improve the method so that the results are more reliable or more accurate.
Show mark scheme for question 8
- repeat each activity more times and calculate a mean (1)
- use more people (of the same age and fitness) (1)
- count the pulse for longer than 15 s, e.g. 30 s or 60 s / use a pulse sensor or heart rate monitor (1)
- use a fixed exercise, e.g. step-ups on a step of fixed height at a set rate (1)
- start counting immediately after the activity stops (1)
- Max 3
Question 9
Describe how the heart rate data in question 5 should be presented as a graph.
Show mark scheme for question 9
- bar chart, because the activities are separate categories (1)
- activity on the x-axis and heart rate / beats per min on the y-axis (1)
- bars of equal width that do not touch (1)
- suitable scale using more than half the grid (1)
- Max 3
Question 10
State what is meant by the recovery time and describe how it is measured.
Show mark scheme for question 10
- time taken for the heart rate to return to the resting rate after exercise (1)
- count the pulse every minute after exercise until it is the same as the resting rate (1)
Exam tips
Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026