The body can either reach the oxygen demand aerobically (with oxygen) or anaerobicly (without oxygen). If the body cannot supply enough oxygen to the muscles aerobically (converting glucose and oxygen to energy) it will start producing energy anaerobicly, which means that glucose gets converted into energy without using oxygen, so your body produces a waste product (lactic acid) which causes you to get a ‘stitch’.
Glucose → energy + lactic acid
This way you will acquire an ‘oxygen debt’ which means that you will have to keep breathing hard for a while to get oxygen to the muscles to convert the waste lactic acid into carbon dioxide and water.
In this experiment we will probably only be converting glucose into energy aerobically, considering the exercise we will be undertaking.
Method:
For this investigation we will only need a stopwatch and a step to undertake the activity on. We may also be given a heart monitor; this will make our results more accurate as it measures your pulse rate automatically straight away instead of waiting 30 seconds and counting manually.
Firstly we will take our resting pulse by counting for We will be repeatedly stepping up and down a step 28cm high for periods of 2,4,6,8 and 10 minutes. Afterwards we will take our pulse rate (radial pulse) for 30 seconds afterwards by counting how many beats we can feel, we will then times this number by two (to get the bpm). After each exercise we will relax for five minutes.
It is important that we collect our results as accurately as possible so that we can produce a good graph and come up with a clear conclusion from it. So, to make it a fair test we will make sure that everybody doing the experiment does it at the same time, this means that everybody will be doing the same amount of step ups at a regular rhythm. We did a test previously and worked it out that this is an average 40 steps per minute. Someone in the group will use a stopwatch to time the period of time we will do the exercise for, and they will alert the group when there is 30 seconds left so that everybody has time to find their pulse (this makes counting easier and more accurate). We will take the radial pulse (above the radial artery at the wrist) as it tends to be easier to find than the carotid pulse (above the carotid artery at the neck), we will count how many beats we feel for 30 seconds (this number will then get multiplied by 2 to work out the bpm).
Everybody will also rest for 5 minutes after they have done the exercise so that their pulse rate decreases back down to normal. This means that their pulse rate will not be high to start with and the results will be more accurate when measured from a resting pulse. We will also repeat each experiment three times and take an average, and if there is enough time we will repeat any results which look drastically out of place.
We will measure the output variable and control the input variable. So we will control how much exercise the person does (by controlling the amount of time they do it for) and count how many beats per minute their pulse does.
To make sure that the method is safe if anyone gets to tired we will make them stop and rest.
Here are the results for each person that took part in the experiment:
My results: (Resting pulse- 64bpm)
Jen’s results: (Resting pulse- 89bpm)
Ruth’s results: (Resting pulse- 74bpm)
Kayleigh’s results: (Resting pulse- 76bpm)
Claire’s results: (Resting pulse- 68bpm)
To find the line of best fit I took everybody’s average result for each of the different times, added them all together and then divided them by the number of people who’s results I took. I did not round the answers previously for everybody’s average because I rounded the final answer for the line of best fit at the end.
For example the average results for 2 minutes were 103.7, 143.3, 120.7, 103.7 and 106.7. These together add up to 578.1. If you divide this answer by the number of people (in this case 5) you will get an average. So:
578.1
5
=115.62 or 116bpm.
But, I did not include Jen’s results (red table, pink line on graph) because they were a lot higher than everyone else in the group and it would not be fair to include them as she measured her pulse rate by using a heart monitor, which is different to the manual method which everybody else used.
Here is the table of the overall averages for each length of time we exercised for:
(Average resting pulse = 70bpm)
Conclusion:
After plotting all five sets of results on one graph and drawing a line of best fit (dark blue line) I have came to the conclusion that your pulse rate does increase with exercise to a certain extent, so my prediction was correct.
The line of best fit shows me that as soon as people start to exercise their pulse rate increases dramatically from their resting pulse. On this graph it increases from 70bpm to 108bpm, that’s a total increase of 38bpm after only 2 minutes exercise. From 2 minutes to 4 minutes the rate increased by 20bpm- almost half of what the pulse rate increased by after 2 minutes.
From 4 minutes to 6 minutes the rate increased slightly- by 8bpm. Then from 6 minutes to 8 minutes by only 4bpm- exactly half of what the pulse rate increased by from 4 minutes to 6 minutes. The pulse rate only increased by 1bpm from 8 minutes to 10 minutes- this is when the graph begins to level off.
The graph increases dramatically at the start because your body suddenly needs more energy to be released at the muscles to carry out the activity. This makes you breathe more quickly and rapidly so more oxygen gets into your body through the lungs. This means that your heart needs to beat faster (increasing your pulse rate) to get more oxygen and glucose (carried in the blood in the blood plasma) to your muscles so that respiration can take place in the muscle cells and produce energy.
Your pulse rate begins to increase more steadily after the initial 2 minutes because your body is beginning to reach oxygen supply with oxygen demand (so your heart slows down) and because the exercise we did stayed the same the amount of oxygen and glucose needed at the muscles stays constant. After the initial sudden need for more oxygen and glucose in the muscle cells the heart starts to slow down as it begins to provide the amount of oxygen and glucose needed for the activity.
Your pulse rate eventually levels off because either your body has reached oxygen demand or because your body is burning energy anaerobicly. Although, it is not very likely that your pulse rate levels off because of anaerobic respiration as no one in the group got a ‘stitch’ (from lactic acid being produced). Your heart rate now goes at a constant speed to provide enough oxygen and glucose for the activity your doing.
Evaluation:
I think that my group’s results were quite accurate as every one who took part in the investigation produced a pulse rate graph with the same type of ‘curve shape’; this evidence supports both my prediction and my conclusion. The pink line on the graph was a lot higher than the other results, but this person did have a higher resting pulse than anyone else. This may be because they are less fit than the other people who took part. But, this person did have a heart monitor on so her pulse rate is likely to be more accurate because it can be difficult to count by touch as just after you exercise your heart beats very quickly and it can be hard to distinguish how many beats you can feel- this is the main problem which we came across. This shows that the counting may have not been very accurate, I cannot prove this though as only one person wore a heart monitor.
I think that on the whole the experiment we did was quite an accurate way of investigating if your pulse rate increases with exercise, but not a good way of finding out exactly what your pulse rate is. Although it was a simple, low-tech experiment we still got the basic idea. I can say this because the line made from Jen’s results (who had the heart monitor on) produced the same kind of curve that everybody else’s did, but it was just a bit higher. Therefore, although we may have counted a few beats out we could still come up with the same conclusions from the people tested with or without the heart monitor on. I think that the graph would look different if everybody in the group wore a heart monitor because the lines on the graph would be a lot higher up, but the curves would still be the same.
The only problem we came across was it being hard to count (ad sometimes locate) your pulse, as just after you exercise it beats very fast so it is hard to count the beats. You can also loose count easily if you get distracted.
I think that our experiment went well as we got the results we wanted. If I did the experiment again I would make it so that everybody in the group wore a heart monitor so that we could get a true pulse reading instead of quite a rough count. If a heart monitor was not available to everybody though, to make the results more accurate I would make sure that everybody counts their pulse rate after the 5 minute resting period just to check that it had decreased back down to normal (there was not enough time available to do this in the first experiment). I would also experiment with different types of exercise (high and low impact) to try and find out exactly when your heart rate cannot increase anymore.