Physical activity and breathingSpec 11.1.5, 11.1.10
In short
During physical activity, both the rate of breathing, the number of breaths per minute, and the depth of breathing, the volume of each breath, increase. This brings more oxygen into the body and removes more carbon dioxide. Muscles respire faster and produce more carbon dioxide, and the brain detects the higher concentration in the blood.
During physical activity, your rate of breathing (the number of breaths per minute) increases. Your depth of breathing (the volume of air in each breath) also increases. Together, these bring more oxygen into the body and remove more carbon dioxide.
Investigating the effect of exercise on breathing
- Sit still and count the number of breaths taken in one minute (or count for 30 seconds and double it). This is the resting breathing rate. Repeat and calculate a mean.
- Do a set amount of exercise, such as running on the spot for 2 minutes.
- Immediately count the breaths in one minute.
- Record the rate every minute until it returns to the resting value. To measure depth, use a spirometer to find the volume of each breath, or measure chest expansion with a tape measure around the chest.
- Repeat with different intensities of exercise, allowing full recovery between each.
| Activity | Breathing rate / breaths per minute |
|---|---|
| At rest | 16 |
| After walking | 22 |
| After running | 34 |
The independent variable is the type or amount of exercise. The dependent variable is the breathing rate. Control the time for each exercise and the time of counting, use the same person, and repeat to find a mean.
Percentage change in breathing rate
A student breathes 16 times per minute at rest and 34 times per minute after running. Calculate the percentage increase.
- Increase = 34 − 16 = 18 breaths per minute
- Percentage increase = 18 ÷ 16 × 100
Answer: 112.5% (about 113%)
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanWhy breathing changes during exercise
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean- Muscles respire faster during exercise, so more carbon dioxide is produced.
- The concentration of carbon dioxide in the blood increases.
- This increase is detected by the brain.
- The brain sends signals to the muscles used in breathing, so the rate of breathing increases and the breaths are deeper.
- More carbon dioxide is removed and more oxygen is taken in.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanDo not say that the brain detects a lack of oxygen. For this syllabus, the stimulus is the increased concentration of carbon dioxide in the blood.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026