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Circulatory System

Factors affecting the Rate of Heartbeat

Introduction: (Initial Observation)

Doctors use a stethoscope or take our pulse to determine our heartbeat. Obviously, the rate of our heartbeat can be an indication of our physical health.

The question is “What does it show?” What factors affect the rate of heartbeat?

Factors such as eating, temperature, elevation, illness, age, and size may be examined.

In this project, I will study the effect of age on the rate of heartbeat.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Note: In one science project and one experiment, you only test the effect of one factor on the rate of heartbeat. Many factors such as those suggested above can be studied (one at a time). In this project guide I assume that you want to study the effect of age on the rate of heartbeat. Based on this assumption, I will suggest hypothesis, define variables, and design an experiment. If you want to test any other factor, you may use this guideline and design a similar experiment to test the effect of factors that you choose.

Information Gathering:

Find out about the heart and circulatory system. Read books, magazines or ask professionals who might know in order to learn about the factors that may affect the rate of heartbeat. Keep track of where you got your information from.

Following are samples of information that you may find:

Pretty Cool – It’s My Pulse!

Even though your heart is inside you, there is a cool way to see it work from the outside by feeling your pulse! You can find your pulse by lightly pressing on the inside of your wrist, just below your thumb. It is best to use your index or middle finger of your other hand because your thumb has a pulse of its own. That would make it pretty confusing with all those pulses!

You’ll know that you’ve found your pulse when you can feel a small beat under your skin. Each beat is caused by the contraction (squeezing) of your heart. If you want to find out what your heart rate is, use a watch with a second hand and count how many beats you feel in one minute. When you are resting, you will probably feel around 70 beats per minute. When you run around a lot, your body needs a lot more fresh blood. Your heart pumps faster to supply the fresh blood that your body needs. You may even feel your heart pounding in your chest. Try running in place or jumping rope for a few minutes and taking your pulse again – now how many beats do you count in one minute?

Some Notes:Our math and science lesson was aimed for students to see how exercise affects heart rate. For our inquiry, we decided to use the exercise probe. This probe is used to measure ones heart rate. We used the probe to measure someone’s heart rate while she was resting, then while she was exercising (running, jumping jacks, etc.), and then finally as she was resting again. This will show how the heart rate changes due to exercise compared to when the body is at rest. Students will use the logger pro in order to represent the affect of exercise on heart rate. Logger pro will give a graphical representation of this experiment, which will allow students to interpret the data and read the graph. Students can use this experiment to explore how different levels of exercise affect the circulatory system. If they had more time for further investigation, they could investigate different affects, such as stimulants, on the heart rate.

This activity would work well with students in a freshman or sophomore biology class. These students would also need to have a background in algebra or in an algebra class at the time. The activity integrates math and science in a graphical sense. The mathematics seen in this activity is related to interpreting graphs and being able to find slopes or fitting the data to a curve. The integration comes when we look at the graphs in terms of heart rate and exercise. The biology and math are both used in order to explore the affects of exercise on heart rate. The benefit of this is that students will get a better understanding of how math and science relate and how subjects are not completely separated from one another. It also gives students a way to see how math and science are used in the real world. Many people exercise in one way or another and the affect on their heart rate can be very important. Students get the opportunity to relate math and science to this real situation during this experiment.

Along with the benefits of integrating the two subjects, there is also a benefit to using the probes. Although the probes were not always providing realistic data, they were helpful at some points. If they were working well, students would be able to actually see the data develop and are more likely to understand the concepts of the experiment. This is much more beneficial than being handed data and asked to believe that it is true. Even the poor data was beneficial to students. It is a learning experience for them to interpret this data and explain why it is wrong.

Finally, I would use this activity with students as an aide to studying the circulatory system. I think it would be a great lab for students to explore heart rate. This experiment would be more of an open inquiry where students are not given a lot of instruction and asked to seek relationships between exercise and heart rate. I do not feel that I would present this activity in a math class because I do not feel that it would be as advantageous as other activities with graphing. However, it is a good way to include math in a biology classroom.

The function of the heart is to circulate blood throughout the body.

Pumping blood through the lungs removes carbon dioxide and refreshes the blood with oxygen.

The oxygenated blood is pumped to the body to provide oxygen and nutrients and to remove waste products.







Among the experiments performed by scientists are experimenting the effect of certain chemicals in the rate of heartbeat.

You may click here to see a sample experiment testing the effect of nicotine on the rate of heartbeat of Daphnia (waterfleas).





There are also experiments to study the effects of exercise on the rate of heartbeat.

How to take your pulse?

Step 1

Turn your left hand palm-side up, then place the first two fingers of your right hand along the outer edge of your left wrist just below where your wrist and thumb meet.

Step 2

Slide your fingers toward the center of your wrist. You should feel the pulse between the wrist bone and the tendon.

Step 3

Press down with your fingers until you feel your pulse. Do not press too hard, or you will not be able to feel the pulsation. Feel free to move your fingers until the pulse is easiest to feel.

Step 4

Continue to feel your pulse for a full minute.




What should I do if I cannot find it?

Sometimes the pulse is difficult to locate. Here are some tips that might help:

  • Try holding your arm pointing down toward the floor, if you have been holding it up toward your face.
  • Try using your fingertips to feel the pulse instead of laying your fingers across your wrist. Put your fingertips in different places, stopping for about five seconds in each position to try to feel the pulse before moving to another location. Lift, place, and feel, until you find a spot where you can feel the pulsations well.
  • Try varying the pressure of your fingertips on your wrist. You may need to lighten up or press a little harder to feel the pulse.
  • Try these steps on the other wrist.
  • If you are still having difficulty, ask a friend to follow the steps and find your pulse.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to study the effect of age on the rate of heartbeat.

How about studying the effect of gender on the rate of heartbeat? Do men or women have a higher rate of heartbeat?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The Independent variable is the age.

Dependent variable is the rate of heartbeat.

Possible constants are gender, race, location.

Controlled variables are weather conditions (temperature, humidity, pollution), condition of stomach (full or empty) and physical health.

A note about variables:
All variables other than the independent and dependent variables must either be kept constant or be controlled. In some projects you can keep all variables constant, so you will have no controlled variable. In some others you cannot keep conditions constant so you will control them. For example about whether conditions, you may be able to do all your tests in an air-conditioned room with a constant temperature; otherwise you will have to record the temperature every time you do your experiment and if you see noticeable changes in temperature, then you must consider it in your analysis of results. If temperature is your controlled variable, you must perform all your experiment trials avoiding big changes in the temperature.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Following is a sample hypothesis:

The rate of heartbeat reduce in adults and as people age. My hypothesis is based on my observation that the bodies metabolism slows down as we age because our bodies no longer need to grow.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”



Identify volunteers in different ages from one to 70 that will allow you to take their pulse one morning before breakfast. Select all volunteers from the same gender (all male or all female). Try to have at least 15 people in this range of ages with a relatively even distribution.

Eliminate any volunteer who has any illness, use medication or has known heart disease.

In one day morning measure and record the rate of heartbeat of all volunteers.

If you have more than one person in a certain age, measure the heartbeat of both and take the average for your results.

To measure the rate of heartbeat you may use a stethoscope and a timer or a watch that shows seconds. Count the number of heartbeats in 60 seconds (one minute). If you don’t have a stethoscope, you may take their pulse from their wrist. Practice taking your own pulse before trying it with others. Instructions for taking pulse is available in the gathering information section (above).

Record your results in a table like this:

Age Heartbeat per minute

The ages in the above table are just samples. Your table will have different ages. Also the number of samples or volunteers must be as many as possible. More samples will make your results more reliable.

Use your results table above to make a graph. A line graph is the best for your results.

Other Experiments:

If you decide to test other factors such as weight, elevation, temperature, eating and gender, you must design your own experiment. Following are some guidelines.

Effect of weight: Testing the effect of weight can be done in two different ways. One way is that you select volunteers from same age, same gender healthy individuals and record their weight and their rate of heartbeat. You will then use your results table to draw a conclusion.

The other way is that you do not restrict your test subjects to human and age, instead you test the heart rate of animals and human with different weights. Your test subjects may include anything from mouse to elephant.

Effect of elevation: To test the effect of elevation, you just need a few test subjects. Measure and record the heartbeat of all subject at sea level or at the lowest elevation that you have access to. Then drive to an area with higher elevation and measure the heartbeats again. If you know of a very tall building in your area, you may do your measurements at the ground level and at the highest level of the building.

Effect of Illness: If you have any safe method of gathering information about the rate of heartbeat in patients, you may use such information to determine the effect of disease on the rate of heartbeat. For best results, you will need the type of disease, the rate of heartbeat during illness and the rate of heartbeat after full recovery.

Effect of Exercise on the rate of heartbeat

To test the effect of exercise on the rate of heartbeat gather a group of about 16 same age healthy volunteers and divide them in 4 groups of 4. For the type of exercise select running. The best time for exercise is early morning before breakfast. The best location is a park or any other open space Name the groups as bellow:

1. control group: This group will not run at all. Just measure and record their rate of heartbeat at the beginning and at the end (when all others finished running).

2. Five minutes group: Measure the rate of heartbeat in this group. Then ask them to run for five minutes and then measure their heartbeat again after running.

3. Ten minutes group: Measure the rate of heartbeat in this group. Then ask them to run for ten minutes and finally measure their heartbeat again after running.

4. Fifteen minutes group: Measure the rate of heartbeat in this group. Then ask them to run for fifteen minutes and at the end measure their heartbeat again after running.

Record your results in a data table like this:

Test Subject Running time Heartbeat (Before) Heartbeat (After)
Control 1 0
Control 2 0
Control 3 0
Control 4 0
Five min. 1 5
Five min. 2 5
Five min. 3 5
Five min. 4 5
Ten min. 1 10
Ten min. 2 10
Ten min. 3 10
Ten min. 4 10
Fifteen min. 1 15
Fifteen min. 2 15
Fifteen min. 3 15
Fifteen min. 4 15

Take the average heartbeat rate for each group and write them in your results table:

Test group Running time Average Heartbeat
Before Exercise
Average Heartbeat
After Exercise
Control 0 minutes
Five minute 5 minutes
Ten minute 10 minutes
Fifteen Minute 15 minutes

Make a bar graph:

Make a bar graph with four pairs of bars. Name the pairs as Control, 5 Min., 10 Min., and 15 Min. Each pair consists of two side by side bars. One yellow and one red. The yellow bar shows the heartbeat rate at the beginning of your experiment. The red bar shows the heartbeat rate at the end of the experiment.

Materials and Equipment:

  • Stethoscope (Optional)
  • Timer or watch with seconds hand
  • Notebook and pen for recording your results.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


No calculation is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.