Your heart, lungs and pulse

1Two body systems that work as a team

Your muscles need oxygen to make the energy you use to move. Two body systems work together to bring it to them.

• The respiratory system is your nose, mouth, windpipe and lungs. When you breathe in, air goes down into tiny air sacs in your lungs. Oxygen passes from the air into your blood. Carbon dioxide, a waste gas, passes out of your blood, and you breathe it out.
• The circulatory system is your heart and your blood vessels. The heart is a strong muscle that pumps blood all around your body. Arteries carry blood away from the heart. Veins bring it back. Very thin tubes called capillaries join them. In the capillaries, oxygen leaves the blood and goes into your muscles.

2What happens when you run and jump

When you run, jump or skip, your muscles work hard and need much more oxygen. So your body changes:

• You breathe faster and deeper, to take in more oxygen and get rid of more carbon dioxide.
• Your heart beats faster, to pump more blood to your muscles. That is why your pulse speeds up.
• You get hot and sweat, which helps your body cool down.

If you run and jump often, your heart and lungs get stronger. A strong heart pumps more blood with each beat, so it does not need to beat as fast when you are resting.

3Warm up first

Walk, then jog gently around the playground for 2 minutes. Then do 10 arm circles each way, 20 high knees and 20 heel flicks. Keep this warm-up short today, because you will measure your pulse at rest first.

4How to take your pulse

Your pulse is the beat you feel as your heart pushes blood through a blood vessel close to your skin. Each pulse is one heartbeat.

1. Hold one hand out, palm up.
2. Put the tips of your first two fingers on the inside of your wrist, just below your thumb. Press gently. Do not use your thumb, because your thumb has a pulse of its own that can confuse you.
3. When the teacher says "Go!", count the beats for 15 seconds.
4. Multiply by 4 to get your beats in one minute (60 seconds), because 15 × 4 = 60.

5What do the numbers mean?

• For children over 10 and for adults, a resting pulse is usually between 60 and 100 beats per minute.
• Well-trained athletes often have a resting pulse of only 40 to 60, because their strong hearts pump a lot of blood with each beat.
• After exercise, a fit heart slows down quickly. How fast your pulse falls in the first minutes after exercise is called your recovery. A quicker recovery is a sign of a fitter heart.

6The pulse experiment

Work with a partner who writes down your results. Then swap.

1. At rest: sit still for 2 minutes, then take your pulse.
2. After exercise: skip with a rope, or jog on the spot, for 2 minutes. Take your pulse straight away.
3. After recovery: sit and breathe slowly for 2 minutes, then take your pulse again.

Mutesi's pulse went up by 64 beats per minute when she skipped, and it came down by 44 in two minutes of rest. What happened to yours?

7The talk test

You do not always have a watch. Use your voice instead:

• You can talk and sing: the work is easy.
• You can talk but not sing: you are working your heart and lungs well.
• You can say only a few words: you are working very hard. You can only keep this up for a short time.

8Cool down

Walk slowly around the playground. Breathe in through your nose for 4 counts and out through your mouth for 4 counts. Stretch your calves and thighs, and drink some water.

Try it yourself

Try each one first, then tap Show answer to check.