An investigation was carried out to measure the breathing rate of a student before, during, and after a period of exercise. The results are shown in Table 1.
| Time in minutes | Breathing rate in breaths per minute |
|---|---|
| 0 | 14 |
| 3 | 14 |
| 6 | 22 |
| 9 | 30 |
| 12 | 30 |
| 15 | 16 |

Explain the trend shown in Table 1 from 3 minutes to 9 minutes.