Cambridge Primary (1-6). Stage 3. Science. Learner's Book - Unit 4: Staying alive - Question 10

Sofia and Marcus tested the breaths per minute of two teachers. They recorded the results in this table.

| Person | Age | Prediction at rest | Breathing rate at rest | Prediction after exercise | Breathing rate after exercise |
|:-|:-:|:-:|:-:|:-:|:-:|
| Sofia | 11 | 20 | 26 | 40 | 50 |
| Marcus | 11 | 35 | 27 | 45 | 48 |
| Mr. Zan | 31 | 30 | 23 | 40 | 41 |
| Mrs. Bell | 29 | 25 | 24 | 35 | 39 |

Why does the breathing rate per minute always increase after exercise?