What it shows
The heart beats faster during exercise to supply more oxygen to muscles. After stopping, the pulse falls back to its resting rate, and the time it takes is a simple sign of how the body recovers.
The science
Muscles working hard need more oxygen and energy, so the heart pumps faster and the breathing speeds up. When you stop, the oxygen debt is repaid and the pulse slowly falls. Pulse is felt at the wrist as the push of blood through an artery with every heartbeat.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A stopwatch or a phone timer
- A skipping rope
- A notebook and graph paper
- A chair
- A friend to take readings
- A quiet place
Safety
For this project: Do this only if you feel well and a teacher or parent approves. Stop at once if you feel dizzy or unwell. This project is not a health test and gives no medical advice.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Learn to find the pulse on the wrist, using two fingers and not the thumb.
Sit quietly for five minutes and count the pulse for 30 seconds, then double it for the resting rate.
Skip gently for one minute, without racing.
Sit down right away and count the pulse for 15 seconds, then multiply by 4, repeating every minute.
Continue until the pulse is within five beats of the resting value, and note the time.
Plot pulse rate against time on graph paper from rest through exercise to recovery.
Repeat on three days and find the average recovery time.
Compare with a friend’s graph and talk about why the numbers are not the same.
What you should see
A graph that rises sharply after skipping and then falls slowly back to the resting level. Recovery usually takes a few minutes.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Where can you feel the pulse?
At the wrist or the side of the neck.
2Why does exercise raise the pulse?
Muscles need more oxygen, so the heart pumps faster.
3Why count for only 15 seconds in recovery?
The pulse falls quickly, so a short count catches the change.
4Does a higher number mean a person is unhealthy?
No, one reading cannot tell that; ask a doctor for health advice.
Take it further
Compare pulse recovery after walking, skipping and running the same distance.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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