What it shows
Muscles in exercise need more oxygen and glucose, so the heart beats faster. The time that the pulse takes to come back to normal shows how quickly the body recovers.
The science
Each heartbeat pushes blood through arteries, and you can feel the pulse at the wrist. During exercise muscle cells use more oxygen and glucose and make more carbon dioxide, so the heart beats faster and breathing deepens to supply and remove these. After exercise the heart rate returns slowly to the resting level. A fitter person usually has a lower resting pulse and a faster recovery.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A watch or phone stopwatch
- A chair and a clear space for stepping on and off a low step 20 cm high
- A notebook and graph paper
- A friend to record the times
- Water for drinking after the test
- A pencil
Safety
For this project: Take part only if you are well, and skip the exercise if you have any heart, breathing or health condition. Stop if you feel dizzy, and have an adult supervise at all times.
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.
Step 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 your pulse on the inside of your wrist with two fingers, never the thumb, and press gently.
Sit quietly for five minutes, then count the beats for 30 seconds and double it to get the resting pulse; repeat twice and average.
Step on and off the low step at a steady pace of about one step each second for 2 minutes.
Sit down immediately and count the pulse for 15 seconds, then multiply by 4 to get beats per minute.
Count again every minute for the next 6 minutes, or until the pulse reaches the resting rate.
Record all values in a table with time on one side and beats per minute on the other.
Draw a line graph of pulse against time, with a horizontal line showing the resting rate.
Repeat for a second volunteer, and compare their recovery time and resting rate.
What you should see
The pulse jumps to about 120 to 160 beats per minute after stepping, then falls back over several minutes. Your graph shows a steep drop at first and a slower approach to the resting level.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why does the heart beat faster in exercise?
Muscles need more oxygen and glucose, and the blood must carry them faster.
02Where can you feel the pulse?
At the wrist, the neck or the inside of the elbow.
03Why count for 15 seconds and multiply?
The pulse starts to fall quickly, so a short count is more accurate for that moment.
04What does a quick recovery suggest?
That the person is fit.
Take it further
Test how the pulse rises after different amounts of exercise, such as 30 seconds, 1 minute and 2 minutes of stepping, on different days.
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.
Free ebooks for this project
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