Chapter 7 of 8

All 8 chapters
  1. 1Organs and systems, readunderstood
  2. 2Digestion, readunderstood
  3. 3Nutrients and diet, readunderstood
  4. 4Breathing, readunderstood
  5. 5Gas exchange in the lungs, readunderstood
  6. 6The heart and blood, readunderstood
  7. 7Pulse, breathing and exercise, readunderstood
  8. 8Drugs, alcohol and health, readunderstood

S3.3.7 Chapter 7

Pulse, breathing and exercise

Why do my heart and my breathing speed up when I run?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

  • You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Measure pulse and breathing rate before and after exercise
  • Show the results in a table and a bar chart
  • Explain why both rates rise during exercise

Your body keeps count of its own work. The pulse is how many times your heart beats in one minute. The breathing rate is how many breaths you take in one minute. Here are the results of one test. Draw them first.

Draw it first

Draw the results of the test

  1. Amina's pulse, shown in two steps. First a table with two columns, time and beats per min. At rest the pulse is 72. After a run it is 120. Second the same results as a bar chart, with a bar for at rest and a taller bar for after run, on a scale from 0 to 140 in steps of 20. Labels: time, beats per min, at rest, after run, beats per min.timebeats per minat rest72after run120

    1 Write the two pulse counts in a table, with the unit, beats per minute, at the top.

  2. Amina's pulse, shown in two steps. First a table with two columns, time and beats per min. At rest the pulse is 72. After a run it is 120. Second the same results as a bar chart, with a bar for at rest and a taller bar for after run, on a scale from 0 to 140 in steps of 20. Labels: time, beats per min, at rest, after run, beats per min.020406080100120140at restafter runbeats per min

    2 Draw a bar for each count. The taller bar is the faster pulse.

Amina sat still, then counted the beats at her wrist for 15 seconds. She ran on the spot for one minute and counted again, at once. A bar chart shows the same numbers as bars. The taller bar is the larger number.

A minute is four lots of 15 seconds. So a count in 15 seconds, times 4, gives beats per minute.

See it three ways

With things

Find your pulse at the wrist. Count the beats for 15 seconds. Multiply the count by 4.

As a picture

Three boxes joined by arrows. Count for 15 s, then times 4, then beats per min. Labels: count for 15 s, times 4, beats per min.count for 15 stimes 4beats per min

In words

There are four lots of 15 seconds in one minute. So the count in 15 seconds, times 4, is the pulse for a whole minute.

In symbols

18 × 4 = 72

Worked example

Amina counts 18 beats in 15 seconds at rest. What is her pulse in beats per minute?

  1. A minute is four lots of 15 seconds.
  2. So multiply the count by 4.
  3. 18 × 4 = 72.

Answer: 72 beats per minute

Breathing is counted the same way. One breath is one breath in and one breath out. Kofi counted his breaths for 30 seconds and multiplied by 2.

A bar chart of Kofi's breathing in breaths per minute. The bar for at rest reaches 16 and the bar for after run reaches 30. The scale goes from 0 to 40 in steps of 10. Labels: breaths per min, at rest, after run.010203040at restafter runbreaths per min
Kofi took more breaths each minute after his run.

Everyone is different. A resting pulse is not the same for every person, and there is no one right number. The best test is you against you: compare your own pulse at rest and after exercise.

Both rates went up. Here is why. Working muscles use oxygen faster and make more carbon dioxide. The blood must carry oxygen to them quickly, so the heart beats faster. The lungs must take in more air and clear the carbon dioxide, so you breathe faster. The heart does not make you breathe faster. Both answer the same need.

Boxes with arrows. Muscles work harder, with an arrow down to need more oxygen. From need more oxygen two arrows go down, one to heart beats faster and one to breathing is faster. There is no arrow between those last two. Labels: muscles work harder, need more oxygen, heart beats faster, breathing is faster.muscles work harderneed more oxygenheartbeats fasterbreathingis faster
The muscles need more oxygen, so the heart and the lungs both speed up. Neither one speeds up the other.

After you rest, both rates slow down again. A fair test counts for the same time each time. It starts when you have been still for a few minutes.

Try it

Test your pulse and breathing

You need: a clock or a watch with a second hand, paper and a pencil, a quiet place to sit.

Be safe: Exercise only if you feel well. Stop at once if you feel dizzy or have pain. If you have a heart or breathing illness, ask a health worker first.

  1. Sit still for a few minutes. Count your pulse for 15 seconds, then count your breaths for 30 seconds. A friend can count your breaths for you. Write both numbers down.
  2. If you are well, jog on the spot for one minute. Then sit down and count again at once.
  3. Multiply the pulse count by 4 and the breath count by 2. Draw a table and a bar chart of your own results.

What you will see: Your pulse and your breathing are both higher straight after you run. They slow down again as you rest.

If you cannot try it, this is what happens.
Example results to copy, in two small tables. The first has beats counted in 15 seconds: 18 at rest and 30 after a run. The second has breaths counted in 30 seconds: 8 at rest and 15 after a run. Labels: time, beats in 15 s, at rest, after run, time, breaths in 30 s, at rest, after run.timebeats in 15 sat rest18after run30timebreaths in 30 sat rest8after run15

A wrong idea many people have

Everyone has the same resting pulse, and there is one right number.

Why it feels right: A book or a chart often gives just one number.

The test that breaks it: Ask a few people to count their pulse at rest. Each count may differ, and all of them may be well.

What is true: A resting pulse differs from person to person. Compare your own pulse at rest and after exercise.

Key words

pulse
the number of times your heart beats in one minute, felt as a beat at the wrist.
breathing rate
the number of breaths you take in one minute.
beats per minute
the unit of pulse. A count in 15 seconds, times 4, gives it.
bar chart
a chart where the height of each bar shows an amount.

Back to your guess

The answer is B: Both speed up, because my muscles need more oxygen.

Both speed up because working muscles use oxygen faster. The heart sends more blood and the lungs take in more air.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Amina counts 18 beats in 15 seconds while she sits still. What is her pulse in beats per minute?

    Tap your answer.

    1. Not this one. You added 4 to the count. A minute holds four lots of 15 seconds, so you must multiply by 4. Go to S3.3.7. Try another.

    2. Yes, that is right. A minute is four lots of 15 seconds. 18 × 4 = 72.

    3. Not this one. That is the count for only 15 seconds. A minute is four times as long. Go to S3.3.7. Try another.

    See the answer

    72 beats per minute

    A minute is four lots of 15 seconds. 18 × 4 = 72.

    • If you chose A: You added 4 to the count. A minute holds four lots of 15 seconds, so you must multiply by 4. Go to S3.3.7.
    • If you chose C: That is the count for only 15 seconds. A minute is four times as long. Go to S3.3.7.

  2. The chart shows Amina's pulse. At rest it is 72 beats per minute. After a run it is 120. How many beats per minute higher is it after the run?

    A bar chart of Amina's pulse in beats per minute. The bar for at rest reaches 72 and the bar for after run reaches 120. The scale goes from 0 to 140 in steps of 20. Labels: beats per min, at rest, after run.020406080100120140at restafter runbeats per min
    Tap your answer.

    1. Not this one. You added the two pulses. To find how much higher one is, subtract the smaller from the larger. Go to S3.3.7. Try another.

    2. Not this one. That is her pulse after the run. The question asks how much higher it is than her pulse at rest. Go to S3.3.7. Try another.

    3. Yes, that is right. Subtract the pulse at rest from the pulse after the run. 120 − 72 = 48.

    See the answer

    48 beats per minute

    Subtract the pulse at rest from the pulse after the run. 120 − 72 = 48.

    • If you chose A: You added the two pulses. To find how much higher one is, subtract the smaller from the larger. Go to S3.3.7.
    • If you chose B: That is her pulse after the run. The question asks how much higher it is than her pulse at rest. Go to S3.3.7.

  3. Kofi counts 8 breaths in 30 seconds while he sits still. How many breaths per minute is that?

    Tap your answer.

    1. Not this one. You divided by 2. A minute is two lots of 30 seconds, so you multiply by 2. Go to S3.3.7. Try another.

    2. Yes, that is right. A minute is two lots of 30 seconds. 8 × 2 = 16.

    3. Not this one. That is the count for only 30 seconds. A minute is twice as long. Go to S3.3.7. Try another.

    See the answer

    16 breaths per minute

    A minute is two lots of 30 seconds. 8 × 2 = 16.

    • If you chose A: You divided by 2. A minute is two lots of 30 seconds, so you multiply by 2. Go to S3.3.7.
    • If you chose C: That is the count for only 30 seconds. A minute is twice as long. Go to S3.3.7.

  4. Which is a fair way to compare your pulse at rest with your pulse after a run?

    Tap your answer.

    1. Not this one. The two counts cover different times, so you cannot compare them directly. Count for the same time each time. Go to S3.3.7. Try another.

    2. Not this one. You need a count at rest to compare with. One count alone shows no change. Go to S3.3.7. Try another.

    3. Yes, that is right. A fair test changes only one thing. Here the only change is the run. So the counting time and the resting start stay the same.

    See the answer

    Count for the same time each time, after sitting still for a few minutes

    A fair test changes only one thing. Here the only change is the run. So the counting time and the resting start stay the same.

    • If you chose A: The two counts cover different times, so you cannot compare them directly. Count for the same time each time. Go to S3.3.7.
    • If you chose B: You need a count at rest to compare with. One count alone shows no change. Go to S3.3.7.

  5. Why do you breathe faster when you run?

    Tap your answer.

    1. Not this one. The lungs do not run out. Working muscles use oxygen faster, so you take in more air. Go to S3.3.7. Try another.

    2. Not this one. Breathing faster is not for cooling. Sweating does that. The reason is oxygen and carbon dioxide. Go to S3.3.7. Try another.

    3. Yes, that is right. Working muscles need more oxygen and give out more carbon dioxide. Faster breathing brings the oxygen in and takes the carbon dioxide out.

    See the answer

    The muscles use oxygen faster and make more carbon dioxide, so more air must pass through

    Working muscles need more oxygen and give out more carbon dioxide. Faster breathing brings the oxygen in and takes the carbon dioxide out.

    • If you chose A: The lungs do not run out. Working muscles use oxygen faster, so you take in more air. Go to S3.3.7.
    • If you chose B: Breathing faster is not for cooling. Sweating does that. The reason is oxygen and carbon dioxide. Go to S3.3.7.

  6. From an earlier chapter

    You feel your pulse at your wrist. What are you feeling?

    Tap your answer.

    1. Yes, that is right. Each time the heart squeezes, it pushes blood along the arteries. You feel that push as a pulse.

    2. Not this one. Veins bring blood back smoothly. The beat you feel comes from the heart pushing blood out along an artery. Go to S3.3.6. Try another.

    3. Not this one. Bones do not beat. The beat is the push of blood in an artery, and it keeps time with the heart. Go to S3.3.6. Try another.

    See the answer

    The push of blood along an artery, with each heartbeat

    Each time the heart squeezes, it pushes blood along the arteries. You feel that push as a pulse.

    • If you chose B: Veins bring blood back smoothly. The beat you feel comes from the heart pushing blood out along an artery. Go to S3.3.6.
    • If you chose C: Bones do not beat. The beat is the push of blood in an artery, and it keeps time with the heart. Go to S3.3.6.

  7. Ravi counts 21 beats at his wrist in 15 seconds. What is his pulse in beats per minute?

    See the answer

    84 beats per minute

    21 × 4 = 84.

Keep it

Copy this into your exercise book.

Pulse is beats per minute. Count for 15 seconds and multiply by 4. Both pulse and breathing rise in exercise, because muscles need more oxygen.

Draw: Draw a table of your pulse at rest and after a run. Then draw a bar chart of it.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (799 KB). It opens on any phone.