The pulse is the rhythmic expansion and contraction of the walls of the arteries, caused by the pressure of the blood pumped from the heart. The pulse rate reflects the heart rate and can be easily felt under the skin. The pulse is irregular because it expands as diastole occurs, and relaxes as systole occurs, so it shows the opposite of what the heart is doing at that same time. There are two main points on the body where the pulse can be taken, the chorotic pulse and the radial pulse. The average pulse in a human is between 60 and 80 beats per minute. Diagram 3 shows where each of these pulses are.
Chorotic Pulse
Radial Pulse
Pre-test
Before doing the main experiment I needed to find out my resting pulse rate. I decided to use the chorotic pulse because it was a lot stronger and a lot easier to find. I also used the method used in the medical field by measuring the pulse for 30 seconds then doubling it to get the beats per minute (bpm). In this experiment, to get reliable results I need to do a full body aerobic exercise so that all the body is moving, so it can be controlled and blood is pumped to all parts. For my experiment I have decided to do star jumps so that my arms, legs and full body are being used.
I found my resting pulse rate to be 78 bpm. This is the constant value for my experiment. After doing an exercise I need to reach this pulse rate before doing the next exercise. This will give me reliable results. To test my exercise I did a 2 minute session of exercise to make sure my pulse rate did increase and that the exercise is reliable to give me the predicted results. This will help me write my plan. It gives me the time limits I will do the exercises and how I will measure my heart rate. I also have a resting time limit, this is between 2 and 5 minutes. This resting time depends on the amount of exercise done.
Plan
In my experiment I have decided to do star jumps for different periods of time. Star jumps are where as you jump, in the air, you spread your arms up and out and your legs down and out into a star shape (hence star jump). This is a full body aerobic exercise used by all people for warming up before a sport or as part of a set of exercises. As well as being a full body exercise, it also has an advantage of being controllable. You can control the exercise, for example doing one star jump every second. This will give accurate and reliable results. Below is a plan of what I will be doing.
- Get stopwatch and reset to zero.
- Record and note resting pulse rate.
- Reset stopwatch.
- Begin doing the exercise, start the stopwatch when exercise started.
- Do exercise for the time needed.
- Immediately after stopping exercise, record pulse rate for 30 seconds.
- Double pulse rate to get beats per minute.
- Note beats per minute in table.
- Rest until pulse rate is at same level or as close to as possible, to the resting pulse.
- Reset stopwatch to zero, ready for next exercise.
The stopwatch must always be reset to zero when not is use to keep the results precise and not to get any unreliable results which seem obviously out of place. The stopwatch must also be started the exact moment the exercise is started, to give more accurate results. After the exercise the pulse rate must be brought back to the resting pulse rate to keep reliable results and also so get the exact change in pulse rate after different amounts of exercise.
In the experiment I will measure the pulse rate twice, once before for the resting pulse rate and once after for the pulse rate after exercise. I will use the chorotic pulse, as it is stronger and more reliable. I will be doing 8 different time limits. These are 1 minute, 2 minute, 3 minute, 4 minute, 5 minute, 6 minute, 7 minute and 8 minute. I will do this experiment twice and will take the average of the two so that my results are more precise and reliable results.
Apparatus
- Stopwatch
- Subject (myself)
The stopwatch I decided to use was on a casio sports watch. I used myself as the subject so that I can personally record the pulse rate and the time of exercise that is done. This is for accuracy and reliability.
Prediction
I predict that the more exercise that is done, the higher the pulse rate difference between the resting rate and rate after the exercise. I predict this because as I have stated in my background theory, the factors which affect the heart rate (and pulse rate) are exercise, emotion and some sicknesses. Seeing as exercise is a factor, my prediction may be correct. I have planned my experiment around testing this theory. On the next page is a sketch of what I think the graph would look like. I predict this because at first the pulse rate will increase at a rapid rate, but towards the end, the heart will reach its optimum rate and the pulse rate will ‘tail off’ to a constant level.
Fair Test
Below is a list of variables, which may affect the experiment.
- Type of exercise.
- Amount of time exercise is done for.
- Temperature of environment.
- Health of subject (not ill).
- Age
- Resting time between exercise periods.
The type of exercise, temperature of environment and health of subject will be kept constant. The type of exercise can affect the results because varying the exercise from a full body aerobic exercise to a simpler exercise will give a wide range of results. The temperature of the environment can also affect the results. At different temperatures the heart pumps blood at different rates to retain or lose heat for thermoregulation. The health of the subject is also an important variable to keep constant. As I have mentioned in my background theory, some sicknesses such as fevers can speed up the heart and pulse rate, so to keep the test fair the subject must be in a constant level of health. To keep this constant, I will use the same subject through out the experiment. Age is also a variable that must be kept constant. Different age people have different pulse rates. This is kept constant by having the same subject throughout the experiment.
The variables that will be changed are the amount of time each exercise is done for and the resting tie between each exercise session. I will change the amount of time each exercise is done because to test my prediction of whether the amount of exercise affects the pulse rate, I must change the time the exercise is done for. The resting time between the exercise will also vary because after longer sessions of exercise, more time is needed to get the subjects pulse rate as close to or exactly to their resting pulse rate. After each session I will measure the pulse rate for exactly 30 seconds, and double it to get the beats per minute. I will do this for every reading. I will repeat the experiment for reliability of results and fairness.
Results
Experiment 1
Experiment 2
Experiment 3
Average
For the average pulse rate difference, some of the values were decimals, but it is not possible to get a fraction of a beat so the result was rounded up or down accordingly. I will now plot the average difference for both experiments on a graph. The x-axis will be time and the y-axis will be the average beats per minute difference.
Analysis
From my results tables I can see that my pulse rate changed at a steady rate in each of the experiments. The pulse rate differences for the second two experiments are the same but towards the end of the third experiment it was difficult to get the pulse rate back to 78bpm. The results seemed close together, which shows that my recording was relatively precise.
My graph shows the average pulse rate difference between the resting pulse rate and the pulse rate after exercise. From my graph I can see that in the first few minutes, there is a rapid increase with the values going from 4bpm to 7bpm to 11bpm. This is continued in the middle with the values in a gradual increase from 15bpm to 18bpm. Towards the end an anomalous result occurred with a smaller increase to 20bpm followed with a sharp increase to 24bpm. The last few minutes, the graph tailed off at a constant 24bpm level.
In conclusion my experiment shows that as the amount of exercise increases, the difference between the resting pulse rate and the pulse rate after exercise increases. The experiment also shows that at a certain point the pulse rate ‘tails off’ to a constant value where the heart cannot pump blood any faster. This means my prediction about the pulse rate increasing with exercise was correct. My prediction about the pulse rate reaching an optimum level and eventually tailing off was also correct. This links in with my theory that exercise affects pulse rate, and there is an optimum pulse rate that can be reached.
The theory behind this experiment must be that the pulse rate increases with exercise because the heart has to pump more blood to the muscles to provide food and oxygen for respiration and energy production. There may also be a theory that at a certain point, the pulse rate and the rate at which the heart pumps reaches an optimum level after a certain period of exercise. After the experiment was finished, I discovered that another factor that affected the pulse rate was the fitness of the subject. If the subject was unfit their pulse rate would be different to a person who was more fit.
Evaluation
The results I got from my experiment are relatively accurate and reliable. They do produce quite an accurate curve and doing the experiment three times, I think I got quite reliable results. I did get two anomalous results towards the end of my experiment at 7 and 8 minutes. These results are slightly higher than what would fit in right with the curve, creating n irregular hump at the top of the curve. These anomalous results may be caused by a number of things. Firstly, they may have occurred because one of my experiments was inaccurate and brought the averages too high. They may also be because my heart rate was not lowered to a low enough value close to my resting heart rate. My tables show that there is a sudden jump from 78bpm resting rate, to 80bpm resting heart rate, this shows that my theory that my heart rate wasn’t lowered enough was correct.
I think my results are not good enough to support a firm conclusion. I think this because my results are not very accurate towards the end and I can not be certain that the end will actually be like the one in my results graph. The experiment was only carried out three times. If it was carried out more, it may have given more reliable results and can be used to give a firm conclusion.
One way of improving my experiment would be to use a heart monitor to calculate the heart rates rather than a human doing it. This will be more accurate as it will remove human error, and can give more accurate values. Below is a plan of how an experiment with a heart monitor instead of a human can be carried out.
- Get stopwatch and reset to zero.
- Using heart monitor, record and note resting pulse rate.
- Reset stopwatch.
- Begin doing the exercise, start the stopwatch when exercise started.
- Do exercise for the time needed.
- Immediately after stopping exercise, record pulse rate for 60 seconds using the heart monitor.
- Note beats per minute in table.
- Rest until pulse rate is at same level or as close to as possible, to the resting pulse. This can be done by using the heart monitor.
- Reset stopwatch to zero, ready for next exercise.
This plan will give more accurate and reliable results, with less human error involved. It can be used as an extension experiment.
Bibliography
Letts GCSE Success: Double Award Biology
Eyewitness: Encyclopaedia of Science 2.0