During exercise, your muscles need more oxygen and fuel, so your heart responds by pumping blood faster and more forcefully. This helps deliver oxygen, remove carbon dioxide, and carry heat away from working tissues. The changes can be measured with heart rate, stroke volume, cardiac output, and recovery time.
These ideas connect biology with physics because blood flow, pressure, work, and energy all change when the body moves.
Key Facts
- Cardiac output is the volume of blood pumped per minute: Q = HR × SV.
- Heart rate increases during exercise because muscles need more oxygen and faster waste removal.
- Stroke volume is the amount of blood pumped by one ventricle in one beat.
- A common estimate for maximum heart rate is HRmax = 220 − age.
- Exercise intensity can be estimated with percent max heart rate: intensity = HR / HRmax × 100%.
- Fitter athletes often have lower resting heart rates because each heartbeat pumps more blood.
Vocabulary
- Heart rate
- Heart rate is the number of times the heart beats each minute, usually measured in beats per minute.
- Stroke volume
- Stroke volume is the amount of blood pumped out of one ventricle with each heartbeat.
- Cardiac output
- Cardiac output is the total volume of blood the heart pumps in one minute.
- Oxygen delivery
- Oxygen delivery is the movement of oxygen-rich blood from the lungs and heart to working muscles.
- Recovery time
- Recovery time is how long it takes the heart rate to return toward its resting level after exercise.
Common Mistakes to Avoid
- Confusing heart rate with cardiac output is wrong because heart rate counts beats per minute, while cardiac output measures blood volume pumped per minute.
- Using HRmax = 220 − age as an exact value is wrong because it is only an estimate and individual results can vary.
- Ignoring stroke volume is wrong because a slower heart can still pump a lot of blood if each beat moves a larger volume.
- Assuming a higher exercise heart rate always means better fitness is wrong because intensity, age, health, hydration, and recovery all affect heart rate.
Practice Questions
- 1 A student has a heart rate of 140 beats per minute during a run and a stroke volume of 90 mL per beat. Calculate cardiac output in mL per minute and in L per minute.
- 2 A 16-year-old athlete has an exercise heart rate of 153 beats per minute. Using HRmax = 220 − age, calculate the athlete's estimated maximum heart rate and percent intensity.
- 3 Two runners finish the same sprint. Runner A's heart rate drops from 170 to 110 beats per minute in 2 minutes, while Runner B's drops from 170 to 140 beats per minute in 2 minutes. Explain what this might suggest about recovery and cardiovascular fitness.