3.5.5 Investigating Heart Rate

Key Methods to Investigate Heart Rate:

1. Measuring Resting Heart Rate:

• Use a stethoscope or place two fingers on the radial artery (wrist) or carotid artery (neck).
• Count the number of beats in 15 seconds and multiply by four to calculate beats per minute (bpm).

2. Effect of Exercise:

• Record resting heart rate.
• Perform moderate exercise (e.g., jogging or step-ups) for a set time (e.g., 2 minutes).
• Immediately measure heart rate post-exercise and continue measuring at regular intervals (e.g., every minute) until it returns to resting levels.

3. Using a Data Logger:

• Attach an electronic heart rate monitor or pulse sensor.
• Collect continuous data for heart rate during different activities for accurate analysis.

4. Effect of Stress or Caffeine:

• Measure resting heart rate.
• Introduce a stimulus (e.g., drink caffeinated beverage or perform mental arithmetic).
• Record changes in heart rate at regular intervals.

Factors to Control in the Experiment:

1. Subject Variables:

• Use individuals of similar age, fitness levels, and health status.
• Ensure they have avoided caffeine, alcohol, or heavy exercise before the experiment.

2. Environmental Variables:

• Conduct the experiment in a controlled environment (e.g., same room temperature and conditions).

3. Duration:

• Standardise the duration of activities (e.g., 2 minutes of exercise for all participants).

Results and Interpretation:

4. Resting Heart Rate:

• A normal adult resting heart rate is 60–100 bpm.
• Athletes may have lower resting heart rates due to increased stroke volume.

5. Exercise:

• Heart rate increases during exercise to supply muscles with more oxygen and remove carbon dioxide.
• The rate at which heart rate returns to resting levels indicates fitness level (faster recovery = greater fitness).

6. Caffeine or Stress:

• Both increase heart rate by stimulating the release of adrenaline, which increases the activity of the sinoatrial node (SAN).

Key Terms:

• Heart Rate: The number of heartbeats per minute (bpm).
• Sinoatrial Node (SAN): The heart's natural pacemaker that controls heart rate.
• Pulse: The rhythmic expansion and recoil of arteries as blood is pumped by the heart.

Tips for Exam Questions:

1. Be prepared to:

• Explain why heart rate increases during exercise.
• Describe the effects of caffeine or stress on heart rate.
• Suggest reasons for variations in resting heart rate between individuals.

2. Practice calculating heart rate recovery times and interpreting graphs or tables of heart rate data.

Example Question:

• Why does heart rate increase during exercise?
  • To supply working muscles with more oxygen for respiration and to remove carbon dioxide and other waste products efficiently.