9.1.4B5. Transport in Humans
Investigating Effect of Physical Activity on Heart Rate — Combined Science 0653 - Biology Revision Notes & Topical Questions
5 min read 7 parts Lesson 8 of 15 Unit quiz
Section 1 of 7Measuring heart rate
Taking a pulse
- Taking a pulse Each time the ventricles contract, a surge of blood stretches the artery walls,
- and this can be felt as a pulse at the wrist (radial artery) or the neck (carotid artery).
- Press two fingers gently on the artery, not your thumb, because the thumb has its own pulse which can cause a miscount.
Beats per minute
- Beats per minute Heart rate is the number of beats in one minute.
- Count the pulse for a fixed time such as 30 seconds and double it, or count for the full 60 seconds for better accuracy.
- A stopwatch or timer is needed so every count lasts exactly the same time.
Breathing rate as an alternative
- Breathing rate as an alternative Breathing rate can be measured instead by counting the number of breaths taken in one minute,
- and it also rises with exercise.
Section 2 of 7Method for the investigation
1
Sit the volunteer down and rest for at least three minutes, then measure the resting pulse for one minute and record it as the result for 'no exercise'.
2
Choose a form of exercise, for example stepping on and off a bench, running on the spot or jogging, and ask the volunteer to do it for exactly two minutes.
3
Immediately after stopping, take the pulse again for a fixed time and record it in beats per minute.
4
Let the volunteer sit and rest until the pulse has returned to the resting value, and note how long this recovery takes.
5
Repeat with a different intensity or length of exercise, and repeat each condition at least three times so a mean can be calculated.
6
Plot the mean results on a graph and look for a pattern.
Section 3 of 7Variables
| Type of variable | Example in this investigation | Why it matters |
|---|---|---|
| Independent | The type, intensity or duration of the physical activity | This is the factor you change on purpose. |
| Dependent | Heart rate in beats per minute (and recovery time) | This is what you measure to see the effect. |
| Control | Same volunteer, same time of day, same counting period, same rest before each trial | Keeping these constant makes the comparison fair and the test valid. |
Section 4 of 7Results and what they show
1Resting measurement
- Resting measurement The first reading gives a baseline against which later readings are compared.
2During and just after exercise
- During and just after exercise The pulse rate is clearly higher than at rest, and harder exercise produces a higher rate.
3Recovery
- Recovery The pulse stays raised for a while after the activity stops and then falls gradually back towards the resting rate.
4Presenting the data
- Presenting the data Results for separate activities are best shown on a bar chart because the independent variable is a set of categories.
- If the exercise time is varied in numbers, a line graph is used.
Section 5 of 7Safety and reliability
Safety
- Safety Only use volunteers who are fit and healthy, and let anyone stop immediately if they feel dizzy or unwell.
- Clear the area of obstacles and use a stable step or bench.
Improving reliability
- Improving reliability Repeat each trial and calculate a mean, ignoring any anomalous result after checking for a counting error.
- Use more than one volunteer to see whether the pattern is general, remembering that fitness differs between people.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Pulse | The regular stretching of an artery wall that can be felt each time the heart pumps blood into it. |
| Heart rate | The number of times the heart beats in one minute, measured in beats per minute (bpm). |
| Resting heart rate | The pulse rate of a person who has been sitting still and relaxed for several minutes. |
| Recovery time | How long it takes for the heart rate to fall back to its resting value after exercise stops. |
| Control variable | A factor that is kept the same so that it does not affect the result. |
| Mean | The total of the repeated readings divided by the number of readings. |
Section 7 of 7Exam technique
1
Counting the pulse for different lengths of time in different trials. The counting period must be identical every time.
2
Starting the next activity before the volunteer has fully recovered, which makes the 'resting' value unfairly high.
3
Taking a single reading and treating it as reliable. Repeat each condition and calculate a mean.
4
Drawing a line graph for different types of exercise. Categories belong on a bar chart.
5
Using the thumb to find the pulse, because the thumb's own pulse can be miscounted.
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