Abstract

Objective

Heart rate increases in response to physical activity, and returns, in time, to the baseline level with rest. The goal of this project is to determine whether athletes have faster heart rate recovery times than non-athletes.

Introduction

The human body has about 5.6 liters of blood, which the heart circulates about three times every minute (NOVA, 1997a). Your heart is constantly beating—even before birth!—to keep the blood circulating. The heart of an average 65-year-old person has contracted more than 2.5 billion times. That's a lot of heartbeats!

Experts on cardiac health tell us that the best way to keep our hearts healthy are maintaining a balanced diet, avoiding smoking, and exercising regularly. Exercise that is good for your heart should elevate your heart rate. How much, for how long, and how often? The American Heart Association recommends that you do exercise that increases your heart rate to between 50 and 75% of your maximum heart rate (your maximum heart rate is 220 beats per minute, minus your age) (AHA, 2006). They recommend getting at least 30 minutes of exercise on most days of the week (AHA, 2006).

How quickly does your heart rate return to normal after exercise? Is the recovery time faster for people who exercise regularly than for people who don't?

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• pulse,
• maximum heart rate,
• target heart rate zone,
• aerobic exercise.

More advanced students should study:

• the cardiovascular system.

Questions

• What are some examples of activities that provide aerobic exercise?
• What is the average maximum heart rate for someone your age?
• What is the range recommended for heart rate during exercise?
• How much exercise does your body need each week for good cardiovascular health?

Bibliography

• AHA, 2006. "Target Heart Rates," American Heart Association [accessed August 18, 2006] http://www.americanheart.org/presenter.jhtml?identifier=4736.
• This NOVA website has information on how the heart works and amazing heart facts:
  • WGBH, 1997a. "Amazing Heart Facts," NOVA Online, WGBH, Boston [accessed August 18, 2006] http://www.pbs.org/wgbh/nova/heart/heartfacts.html.
  • WGBH, 1997b. "Map of the Human Heart," NOVA Online, WGBH, Boston [accessed August 18, 2006] http://www.pbs.org/wgbh/nova/heart/heartmap.html.
  • WGBH, 1997c. "Cut to the Heart," NOVA Online, WGBH, Boston [accessed August 18, 2006] http://www.pbs.org/wgbh/nova/heart/.
• This site has a Java applet you can use to make printable, color graphs of your data:
  NCES, 2006. "Create a Graph," National Center for Education Statistics, U.S. Dept. of Education [accessed August 18, 2006] http://nces.ed.gov/nceskids/createagraph/.
• If you need help with using a spreadsheet program, the following tutorial will be useful:
  James, B., date unknown. "Excel 101," University of South Dakota [accessed August 18, 2006] http://www.usd.edu/trio/tut/excel/.
• This website has descriptions and calculators for several statistical tests, including the Student's t-test that you can use in this project to calculate the statistical significance of your results:
  Kirkman, T., date unknown. "Student's t-Tests," Department of Physics, College of St. Benedict & St. John's University [accessed August 18, 2006] http://www.physics.csbsju.edu/stats/t-test.html.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• volunteers:
  • 50–100 subjects for each group you want to compare (more is better, see the Science Buddies resource, How Many Participants Do I Need?);
  • exclude people who have medical conditions that prevent them from engaging in vigorous physical exercise (e.g., people with heart conditions or severe asthma).
• surveys (see Experimental Procedure section),
• clock with second hand,
• lab notebook,
• calculator or computer with spreadsheet program.

Experimental Procedure

Note: There are special considerations when designing an experiment involving human subjects. ISEF-affiliated fairs often require an Informed Consent Form for every participant who is questioned or observed. In all cases, the experimental design must be approved by the fair's scientific review committee (SRC) prior to the commencement of experiments or surveys. Please refer to the ISEF rules for additional important requirements for studies involving human subjects: http://www.sciserv.org/isef/document/.

1. Do your background research and make sure that you are knowledgeable about the terms, concepts, and questions, above.
2. For this project, you will need to become proficient at measuring heart rate. Practice finding your pulse and measuring your own heart rate so that you can do it quickly and easily. Then practice measuring a helper's heart rate until you can do it quickly and easily.
3. You will need to write a short survey to determine the activity level of each of your volunteers, in order to assign them to the "athlete" or "non-athlete" group. Your survey should gather the following information:
   1. participant's age,
   2. participant's gender,
   3. participant's activity level: e.g., ask how many times per week they get aerobic exercise, and have them classify the exercise as minimal, moderate, or intense.
4. Use the survey results to define two groups, "athletes" and "non-athletes," based on the amount and intensity of regular exercise.
5. Use the following procedure for each participant:
   1. Measure and record the participant's resting heart rate, and the time.
   2. Have each participant engage in a vigorous activity for at least 2 minutes. Choose a time and use it for all participants. Try the exercise yourself beforehand to be sure that the time is reasonable. The exercise could be jumping rope, stepping on and off a low stool, jogging in place or around a track, etc.
   3. Immediately after the end of the exercise period, have the participant sit and rest. Measure and record their heart rate, and the time.
   4. While the subject continues to sit and rest, monitor their heart rate at 1- or 2-minute intervals until two measurements in a row have returned to the resting rate (or below). Record the time of each measurement.
6. For each subject, calculate the heart rate recovery time (time from end of exercise until heart rate returns to baseline).
7. Calculate the average heart rate recovery time and standard deviation for each group (athletes vs. non-athletes).
8. Another measure you may wish to calculate is the decrease in heart rate in the first two minutes after exercise. Subtract the heart rate at the two-minute rest point from the peak heart rate (taken immediately after exercise).
9. Other group statistics you may also want to calculate:
   1. average and standard deviation of resting heart rate,
   2. average and standard deviation of peak heart rate (immediately after exercise period).
10. More advanced students should use Student's t-test to determine whether any differences between the two groups are statistically significant.
11. You could also make line graphs of heart rate vs. time for each participant. Use graph paper, a spreadsheet program (like Excel), or Create a Graph. Compare the graphs. Can you identify the athletes and non-athletes from the shape of the graph alone?

Measuring Heart Rate

1. Use the first two fingers of one hand to find the radial pulse on the inside surface of the wrist (see Figure 1). You will find it on the "thumb side" of the wrist, just below the base of the hand. Practice finding your pulse until you can do it quickly. Note: don't use your thumb, because it has its own pulse, which could throw off your count.

   Figure 1. The photo shows how to find the radial pulse.

2. The heart rate is the number of beats per minute, but you don't have to count for a full minute to get an accurate measurement. Counting the number of beats in either 10 or 15 seconds is fine. Use the clock to time your count, and write down the number of beats you counted in your lab notebook. Then calculate the number of beats per minute to get the heart rate. If you counted for ten seconds what do you need to multiply by to get the number of beats per minute? How about if you counted for 15 seconds? That's it!

Variations

• For a related project on lung capacity, see the Science Buddies project: Breath of Life: Does Exercise Increase Vital Capacity?
• Do heart rate recovery times increase with age? Design an experiment to find out. Try to think of ways to address the issue of activity levels changing with age. Can you separate the two variables of age and activity level?
• Do smokers have increased heart rate recovery times compared to non-smokers? Design an experiment to find out. Again, it is possible that differences in activity levels might be part of the difference, so see if you can think of a way to separate the two variables of smoking history and activity level.

• For more science project ideas in this area of science, see Human Biology & Health Project Ideas.

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

The idea for this project is from:

• Marsh, M.K., 2003. "How Quick Is Your Heart Rate Recovery?" California State Science Fair Abstract [accessed August 18, 2006] http://www.usc.edu/CSSF/History/2003/Projects/J1010.pdf.

Last edit date: 2011-10-26 12:00:00