Two girls on a track team recorded their heart rates before, during and after a short exercise.
Use the graph below and what you know about the human body and homeostasis to answer the questions that follow.
**Heart Rate Data for 2 Girls Before, During, and After Exercise**
Girl A:
- Before exercise: 70 bpm
- During exercise: 180 bpm
- After exercise: 90 bpm
Girl B:
- Before exercise: 80 bpm
- During exercise: 190 bpm
- After exercise: 100 bpm
1. **What is the heart rate response to exercise for each girl?**
- Girl A's heart rate increased from 70 bpm before exercise to 180 bpm during exercise, and then decreased to 90 bpm after exercise.
- Girl B's heart rate increased from 80 bpm before exercise to 190 bpm during exercise, and then decreased to 100 bpm after exercise.
2. **Explain the physiological reasons behind the changes in heart rate during exercise.**
- During exercise, the body requires more oxygen and nutrients to be delivered to active muscles. The heart rate increases to pump more blood (and therefore oxygen and nutrients) to meet this increased demand. This is a normal response of the cardiovascular system to physical activity.
3. **Why does heart rate decrease after exercise?**
- After exercise, as the body starts to recover and return to its resting state, the heart rate gradually decreases. This is because the demand for oxygen and nutrients by the active muscles decreases, and the body no longer needs to work as hard to supply them. Homeostasis is achieved as the body returns to its baseline heart rate.
4. **Based on the data and the knowledge of the cardiovascular system, which girl likely has better cardiovascular fitness?**
- Girl B likely has better cardiovascular fitness as her heart rate at rest (before exercise) is higher than Girl A's. A higher resting heart rate can indicate a more efficient cardiovascular system that is able to pump blood more effectively at rest. Additionally, Girl B's heart rate during exercise is higher, which could suggest that her heart is able to work harder and sustain higher levels of activity.