Heart Rate and Exercise

The radial pulse point is the safest location to take someone's pulse.
Staff Sgt Jeanette Copeland, courtesy of the US Airforce.

Grades:
Length: Variable

Overview

Students measure and compare their heart rates before and after a variety of physical activities, and also compare their heart rates to those of other students in their groups.

This activity is from The Science of the Heart and Circulation Teacher's Guide, and was designed for students in grades 6–8. Lessons from the guide may be used with other grade levels as deemed appropriate.

Safety Note: Do not have students use the carotid artery in the neck to find their pulse. Applying too much pressure there could stimulate a reflex mechanism that can slow down the heart. The radial pulse point is the pulse site recommended for the general public by the National Heart, Lung, and Blood Institute, National Institutes of Health.

Teacher
Background
Objectives and Standards
Materials and
Setup
Procedure and
Extensions
Handouts and
Downloads

Teacher Background

Almost every day, we see, hear or read in the media about the importance of exercise for heart health. Why? What is the relationship between the heart, circulation, and exercise? This activity will help students learn how their hearts respond to physical activity.

Even when you are sleeping, reading, or watching TV, your muscles, brain, and other tissues use oxygen and nutrients, and produce carbon dioxide and wastes. If you get up and start moving, your body’s demand for oxygen and the removal of carbon dioxide increases. If you start running, your body demands even more oxygen and the elimination of more carbon dioxide. The circulatory system responds by raising the heart rate (how often the pump contracts) and stroke volume (how much blood the heart pumps with each contraction), to increase the cardiac output (the amount of blood pumped from the left ventricle per minute). During exercise, heart rate can rise dramatically, from a resting rate of 60–80 beats per minute to a maximum rate of about 200 for a young adult.

While you are running, blood flow is diverted toward tissues that need it most. For example, muscles in the arteries in your legs relax to allow more blood flow. Meanwhile, muscles in the walls of the arteries that take blood to your stomach and intestines tighten, or constrict, so these organs receive less blood. Breathing rate increases to match greater output by the heart. The whole system works together to give your hard-working muscles what they need at just the right time.

Have you noticed that after you finish a run, your heart rate and breathing rate don’t return to normal immediately? Why? It’s because the circulatory and respiratory systems have to “catch up.” You may not have realized it, but while you were running, the muscles of your body produced so much carbon dioxide and other wastes that the body’s systems couldn’t keep up with the increased demand for elimination. So even after your run ends, your heart rate and breathing rate remain elevated until the excess wastes are eliminated.

If the heart and circulatory system have to do so much extra work when you exercise, why is exercise good for you? One simple answer is, “Use it or lose it.” The heart is a pump made of muscle. It needs regular exercise to remain strong, healthy and efficient. The same is true of the circulatory system. Exercise helps keep the arteries strong and open. The contraction of leg muscles during exercise helps to move the blood along. Without exercise, body chemistry actually changes. These changes can lead to a whole range ofunhealthy conditions and diseases. Bottom line: to maintain a healthy heart pump and circulatory system, “use it.”

The pumping heart makes the sound we refer to as the “heartbeat.” The “lub-dub” of a heartbeat comes from the sounds of blood being pushed against closed, one-way valves of the heart. One set of valves (tricuspid and bicuspid) closes as the ventricles contract. This generates the “lub” of our heartbeat. The other set of valves (pulmonary and aortic) close when the pressure in the ventricles is lower than the pressure in the pulmonary artery and aorta. This leads to the “dub” of our heartbeat.

As the heart beats, it presses the blood against the muscular, elastic walls of the arteries. Each artery expands as blood is forced from the ventricles of the heart. The artery wall then contracts to “push” the blood onward, further through the body. We can feel those “pulses” of blood as they move through the arteries in the same rhythm as the heart beats. The number of pulses per minute is usually referred to as pulse rate. The average pulse rate for a child ranges from 60 and 120 beats per minute.

This activity is adapted with permission from the HEADS UP unit on Diabetes/Cardiovascular Disease (2003). The HEADS UP unit was produced by the Health Education and Discovering Science While Unlocking Potential project of The University of Texas School of Public Health (www.sph.uth.tmc.edu/headsup) and was funded by a Science Education Partnership Award from the National Center for Research Resources of the National Institutes of Health.

Objectives and Standards

Life Science

Different tissues are, in turn, grouped together to form larger functional units, called organs. Each type of cell, tissue and organ has a distinct structure and set of functions that serve the organism as a whole.
Specialized cells perform specialized functions in multi-cellular organisms. Groups of specialized cells cooperate to form a tissue, such as a muscle.
The human organism has systems for digestion, respiration, reproduction, circulation, excretion, movement, control and coordination, and for protection from diseases. These systems interact with one another.

Science in Personal and Social Perspectives

Regular exercise is important to the maintenance and improvement of health. Personal exercise, especially developing cardiovascular endurance, is the foundation of physical fitness.

Science, Health and Math Skills

Measuring
Observing
Interpreting data
Applying knowledge

Materials and Setup

Teacher Materials (see Setup)

Stopwatch or watch with a secondhand
CD player or other player for music
Two music selections without words (one song with a strong, up-tempo beat, and a second song that is slow and relaxing)

Materials per Student

Access to a clock or watch with a second hand (or one stopwatch per team of students)
Copy of student sheet (see Lesson pdf)
Optional: Lab notebook

Setup

Read all instructions before beginning.
Select appropriate music.
Data collection can be done individually by students or in teams of two, but data analysis should be done by students in groups of four.

Procedure and Extensions

Time: Two class periods of 45-60 minutes, one to collect data and one to process, present and interpret measurements.

Ask students if they think heart rate can vary, or if it always is the same. Ask, What kinds of situations might cause heart rate to change? [exercise, nervousness, lying down, standing up, walking up stairs, etc.]
Show students how to measure heart rate (beats per minute) by feeling blood surge through an artery. Have each student find his or her pulse by placing slight pressure on the wrist with the middle and ring fingers. Tell students not to use the thumb, as it has a pulse of its own.

Allow students to practice counting their pulse rates several times while you count off 15-second intervals. Instruct students to multiply their pulse count by four to determine how many times their hearts beat in one minute.
Distribute the student sheet to each student.
Review the activity sheet with students, stopping periodically to ask questions and make sure they understand the content.
Ask students to complete the prediction section for the first activity. Explain that predictions should be made in order, and for only one activity at a time. (The outcome of each activity may influence their predictions for the next.)
Have students sit quietly for minute. Then, instruct them to count their pulses while you time them for 15 seconds. To establish their resting, or beginning, pulse rates, students should multiply by four the number of pulses they counted in 15 seconds. Have them record this number on their activity sheets.
Instruct the class to sit quietly and listen to soft music for one minute. Then, have all students measure /record their pulse rates once again. Continue to lead students, as a class, for the first three activities on the sheet. During the deep breathing exercise, make a point of telling students when to inhale and exhale, to be sure they maintain a very slow rate. Instruct students to continue this pattern of slow breathing as they take their pulses.
Explain that students should complete the remaining activities listed on the sheet, in order. Each student may work with a partner, if desired. Remind students to record their pulse rate predictions at each step. Students should apply previous experiences when making each new prediction. Be sure students have sufficient time to regain their resting pulse rates before beginning each activity. You may wish to have students record the time it takes for them to return to their resting heart rates. (Pulse rates will recover more quickly if students are seated.) Some students may notice that their heart rates fall below their resting heart rates before returning to normal.

Be sensitive to students who may feel uncomfortable doing jumping jacks or sit-ups in front of the class.
Instruct students to complete the data collection, analysis and conclusion portion of the activity sheet.
Have students form groups of four. Each group should share its data, create a presentation of its collective results (graph, table, picture, etc.), and give its presentation to the class.
Ask, What have you learned about heart rate? Students should have been able to observe that heart rate increases with increased levels of activity. Ask students, What happened to your breathing during activities that increased your heart rate? Students should have noticed that with physical activity, breathing rate and volume of air taken in increased. Help students to understand the connection between the body’s need for more oxygen during exercise and the heart’s effort to deliver oxygen (by pumping blood more quickly).
To conclude the activity, have students write a journal entry describing connections between the intensity of activity and heart rate. Students should complete the following statements, and may want to draw pictures to accompany their words.
- I discovered…
- I learned…
- I never knew…
- I was surprised…
- I enjoyed…
Have students add any new knowledge or ideas to their group concept maps.

Extension

Ask students, Why would an athlete have a slower resting heart rate than a non-athlete? Remember that the average resting heart rate for an adult is 72. Consider the following average resting heart rates in beats per minute (bpm).
- Weightlifter: 65 bpm
- Football Player: 55 bpm
- Swimmer: 40 bpm
- Marathon Runner: 40 bpm

Ask, Why would a slower heartbeat during rest indicate a healthier heart? Explain that regular exercise strengthens the heart, and that a well-conditioned heart can pump the same amount of blood with fewer beats. In addition, cardiovascular exercise increases the size of cardiac muscle cells and the size of the heart chambers, so the heart actually increases in size. Therefore, even though the amount of beats per minute is lower, a healthy, fit heart pumps more blood per minute than a heart that is not accustomed to exercise. For the best health, exercise must be a lifestyle, not a temporary fitness “kick.” Studies have found that non-activity for as little as three weeks can reduce heart muscle size and stroke volume (amount of blood pumped from the left ventricle in one contraction).