Fun and easy science experiments for kids and adults.

Taking the pulse

Take your pulse during rest and exercise. This is an experiment about the body's circulatory system.

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Video

Materials

Your body
A clock

Step 1

Rest for 5 minutes.

Step 2

Press with your index and middle finger on the inside of the wrist in order to feel your pulse. Is it slow or fast? If you want, count the number of beats in a minute (or the number of beats during 15 seconds and multiply by 4).

Step 3

Play for 5 minutes.

Step 4

Again feel your pulse. Is it slow or fast? If you want, count the number of beats per minute.

Short explanation

The heart rate increases because the muscles need more oxygen, and also to get rid of the carbon dioxide they produce.

Long explanation

The heart pumps blood throughout the body. The blood has several tasks, including transporting oxygen. The pulse is the result of the heartbeats. Every time the heart contracts and pumps blood in the body, it is felt in the form of an increase in pressure in the blood throughout the body. The more often the heart beats, the more blood passes through the body every minute.

You move by contracting muscles. For the muscles to be able to do this, they require energy. More specifically, it is the cells that make up the muscle that require energy. This energy (glucose, also called "blood sugar") reaches the muscle cells through the blood. An increased glucose requirement is mainly satisfied by the action of hormones, so this is not the explanation for the increase in heart rate in this experiment.

The increased heart rate is instead due to the fact that the blood needs to transport more oxygen to the muscle cells, as well as transport more carbon dioxide away from the muscle cells. The muscle cells need oxygen to break down the glucose molecules and release the energy contained in them. And in this process, carbon dioxide is formed as a by-product, which is toxic to the muscle if it accumulates in excessive amounts.

Oxygen is transported in the blood bound to red blood cells, which are very small and specialized cells. Carbon dioxide is also to some extent transported bound to red blood cells, but mainly in the water that the blood contains.

Normal heart rate at rest is 60-80 beats per minute and at moderate exercise 120-150 beats per minute.

Experiment

This is actually already an experiment, but you can keep experimenting. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

What is your heart rate during a range of activities?
How high a heart rate can you get?
How low a heart rate can you get?

Variation

Instead of comparing your heart rate at rest and exercise, you can compare the respiratory rate, i.e. how often you breathe.

Increasing the heart rate is not really enough to increase the supply of oxygen to the muscles. After a while, the blood is depleted of oxygen! So how does the blood get its oxygen? Well, in the lungs of course. Every time the blood flows through the body, it passes through the lungs, and there the red blood cells pick up oxygen. The oxygen enters the lungs by us breathing, which is when we expand the lungs using muscle power and create a negative pressure, whereupon the air is sucked in.

The more the muscles work, the greater is their oxygen demand, and the more oxygen must be supplied to the lungs. Therefore, we need to breathe more often.

Normal respiratory rate at rest is 12-15 breaths per minute and at moderate exercise 30-50 breaths per minute.