Written in 8th grade


The body needs energy for all kind of activities. When the body is resting, it needs lower amount of energy. But the more demanding activities we are doing, the more energy is needed.

The main source of energy is carbohydrate and fat. The fat and carbohydrates are transformed by the ‘citric acid cycle’ into energy. The chemical energy is transferred to a substance that is called ATP (adenosine triphosphate). The ATP is a small package of energy that is used by the cells. In aerobic respiration oxygen is needed. The waste products are water, carbon dioxide and heat.

The oxygen (O2) and carbon dioxide (CO2) is transported to/from the cells by the hemoglobin in the blood from/to the lungs. It is in the lungs, in the border between the capillaries and the alveoli, where the gases are exchanged by diffusion. The heart is the pump which makes the blood circulate in the body. And our breathing enables new air (with O2) to enter the lungs by inhaling and get rid of the old air (with CO2) by exhaling.

Therefore with more demanding exercises (eg. running) more energy is needed and therefore also more oxygen is needed (in the citric acid cycle) and more carbon dioxide is produced. Therefore the heart and breathing rate is becoming higher to enable the transportation of carbon dioxide and oxygen.

Normal resting heart rate for an untrained man is 70 - 75 bpm. And it's lower for people that are well trained, it can be low as 25 bpm. And for old people it is higher. Normal breathing rate/min is 13 - 16

With this lab I want to find out how activities affect the heart and breathing rate in humans.

Hypothesis: I think that the heart and breathing rate will increase during activity.


  • Stopwatch
  • Calculator
  • 2 testpersons (boys, 14 years)

Our activity was to jump on the same place for 15s (seconds).

  1. I measured the testpersons heart rate by putting a finger on the neck and controlling how many times the heart beats in 15s.
  2. I measured the testpersons breathing rate by counting how many times they exhaled in 15s by holding a hand in front of the persons mouth (around 20 cm away).
  3. The testpersons jumped on the place for 15s.
  4. I measure the heart rate as in 1
  5. I measured the breathing rate as in 2.
  6. I multiplied all results that I measured in 15s by 4, so I got the results per minute (60s) instead.



The aim of this lab was to find out how activities affect the heart and breathing rate in a human. In my lab, I can easily see that the heart and breathing rate become higher during activity.

My data isn't 100% reliable because that measurement that I used wasn’t so good, eg. I measured for 15s and then I multiplied it by 4. If I would make a more accurate lab, I would measure in 60s. Or if even more correct, I could measure for 120s and divide by 2. It would be more accurate if I did like this, because when I measured for 15s and multiplied it by 4, it might be up to 2 heartbeats wrong when I started to measure and up to 2 heartbeats wrong in the end, then I multiply it by 4, so I could get up to 16 heartbeats wrong per minute. But if I measure for 60s, it could be up to 2 wrong in the beginning and up to 2 wrong in the end, which would mean that I would only get up to 4 heartbeats wrong per minute. Eg. if the accurate heartbeat/min is 70, it would be somewhere between  54 bpm and 86 bpm if I measured in 15s, if I measured in 60s it would be somewhere between 66bpm and 74bpm (which is much more reliable).
If I would do the lab even more accurate, I could use a professional pulse and breathing meter and have a treadmill for the testpersons to run on, so the testpersons would make exact the same activity.

In this lab the resting heart rate and the resting breathing rate were much higher than normal. The reason for this was probably that I didn’t measured the real resting rate for pulse and breathing. The persons was probably not relaxed. So in next lab I would make sure that the persons are relaxing.

It would be interesting to measure the heart and breathing rate on a smoker or a person that has certain health problems as eg. asthma, or a person that lives in a place where the environment is polluted, and how they respond to exercise, and compare to my results.

In these persons, the gas exchange is slower, and smoking also has that negative effect that the hemoglobin can bind less oxygen because of it is occupied of carbon monoxide (CO). So if I would make a new study with persons in this group, I would probably get the results that their heart will beat faster and they will have much harder to make exercices.

According to the literature obesity, alcohol and drugs can affect a person’s heart and breathing rate. For example alcohol depresses both heart and breathing rate, which makes it harder to make exercices. Some drugs (medicines) can change the heart rate or make it easier to breath, eg. asthma drugs (eg. ventolin) make the muscles around the bronchi relax so that the tubes open and it is easier to breathe. Other drugs as nitroglycerine is used in angina pectoris and it makes the arteries around the heart becoming broader and let more blood pass to the heart and lower the heart rate.

When we don’t use the energy sources (fat, carbohydrates and proteins) that we eat, they get stored as glycogen and fat. If there is too big excess of energy sources, one become fat. Fat people have more mass and weighs more than not fat people, so they also need more energy and oxygen to do activities. Too much fat in the diet stops muscle cells to take up glucose from the blood and makes the cells to slow down the release of needed energy.



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  • Human Physiology, The Mechanisms of Body Function
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