lkteja
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### effect of caffeine on heart rate

Hi,

I am a 5th grader choose the topic 'effect of caffeine on heart rate'. I need some guidance to get the entire experiment as I could not see this experiment in Science Buddies website. I need help especially in determining the variables the I need to keep the same and change. [ like the controlled/measureable]

1. Should i use 3 different drinks having caffeine but same measurement of caffeine in each of the drinks. For eg, if i choose soda and it has 325 mg of caffeine, i should chose coffee having same 325 mg of caffeine otherwise the heart rate for each drink having different amount of caffeine differs as it all depends on the caffeine amount? I am right?

2. I have the idea to do 3 trials but stuck here.

3. I am planning on testing the drinks on adults [men and women] of 2 age groups 40-50 yrs and 60-70 yrs. Under what variables this will come?

4. I want to also make a model of heart related to this topic. any help on how to make a model of heart that shows my experiment.

thanks

nguyenmccarty
Former Expert
Posts: 53
Joined: Thu Sep 21, 2017 11:09 am
Occupation: University cell and molecular biologist

### Re: effect of caffeine on heart rate

Hi there!

1. I'm not exactly sure what your question is here.
If you're interested in how caffeine affects heart rate, a more controlled experiment might be to give different people different amounts of the same drink. For example, say you choose a coffee that contains 300 mg of caffeine per 8 oz. Then one group of people might be assigned to consume 4 oz coffee, or 150 mg caffeine, while a second group might consume 8 oz coffee / 300 mg caffeine. In this way, you change the amount of caffeine given, but keep the same source of caffeine.
The reason this is better than giving one group coffee and another soda is that the caffeine in coffee vs. soda might be absorbed at different rates based on other components in each drink. Another variable that might influence your results would be the sugar that is in the soda but absent from plain coffee.
On the other hand, if your question is about how the source of caffeine affects its influence on heart rate, then yes, you would definitely want to choose a soda drink and a coffee drink with the same amount of caffeine. In that experiment, the variable you keep constant is the amount of caffeine, and the variable you change is the source of the caffeine.
If this doesn't address what you're asking for help on, perhaps you can clarify and I might be better able to help guide you.

2. Again, I'm not quite sure what you're asking. Whatever variable you decide to test based on part 1, at a minimum you want to have several people in each group, because individuals can have different reactions and/or sensitivities to caffeine.
On top of that, it wouldn't be a bad idea to complete this experiment on each of your test subjects 3 times (on different days, or at least several hours apart to make sure the results of trials 2 and 3 aren't being influenced by leftover effects from the caffeine consumed in trial 1).

3. In this case, age is your independent variable: you are the one controlling it and grouping your subjects into one age range or the other. Then your dependent variable will be their change in heart rate after consuming caffeine.

Good luck, and let me know if there is anything I can still clarify for you!

lkteja
Posts: 8
Joined: Sat Apr 01, 2017 10:06 am
Occupation: Student

### Re: effect of caffeine on heart rate

Thank you for the reply.

My Q is ' What is the effect of Caffeine on heart rate?'

So, as you mentioned in point 1, that different sources of caffeine would affect the heart rate, then I would keep the same one source of caffeine like plain coffee rather than using soda and coffee for my 3 trials. Here is the my understanding after reading your reply. Pls correct me if I am wrong.

1. Since you have mentioned that sugars along with caffeine in soda will impact or affect the heart rate, I better stick to only one source of caffeine, plain coffee, with the quantity like 4 oz and amount of caffeine is 300 mg, in trial 1. Then for trail 2, I will use the same source of caffeine like plain coffee but now 8 oz and with little higher dose of caffeine in it , eg 325 mg. Then trial 3, again same source of caffeine but now 10z with caffeine dosage is 350mg. Is this okay.

First, I have to take the heart rate without caffeine and then after the subjects drink the plain coffee, I have to take the heart rate.

2. Another Q, also should I then go for plain coffee without any milk or half and half or sugar added to it in order to address perfectly my Q for this experiment, ‘What is the effect of caffeine on heart rate?’

3. So far I am thinking the following come under each category of variable. Let me know if i am missing anything for the variables.

Controlled: Caffeine, heart rate at rest [before drinking plain coffee], time [same time of each day, 3 days for 3 trials], same chair where the subject sits.

Manipulated: Quantity of plain coffee [2 oz trial1, 4oz trail2, 80ztrail3], amount of caffeine, Gender[ women/men], Age, different days [Mon trial1, Tues trail2, Wed trail3]

Responding: Heart rate after consuming coffee

4. Also, should the subjects not eat or drink for 2hrs before I start testing their heart rate to drink the coffee.

thank you

nguyenmccarty
Former Expert
Posts: 53
Joined: Thu Sep 21, 2017 11:09 am
Occupation: University cell and molecular biologist

### Re: effect of caffeine on heart rate

1. Yes, you're right that if your experimental question is simply, "How does caffeine affect heart rate?," then the most controlled way to ask this question will be to use a single source of caffeine for all subjects and trials. However, if you plan to do 3 (or any number of) trials, every trial should be exactly the same. In other words, choose the experimental groups or variables you'll test, then test them in the exact same way for each trial. (Don't, for example, give subjects a different amount of coffee at each trial.)
The reason scientists perform several, identical trials of every experiment is that on any given day, an observed response may be a real result, or it may simply be the effect of something out of their control and not accounted for when interpreting the results. For example, in this case: let's say caffeine increases heart rate. But maybe one day, one of your subjects' beginning heart rate (before coffee) may be already elevated from normal because they just climbed a flight of stairs, had a bad day at work, etc. In this case, you might not see a further increase in their heart rate due to the caffeine, leading to the mistaken conclusion that caffeine does not affect heart rate.

2. You're right, the best way to ask this question means giving each person plain coffee. It's possible that the sugar and/or milk some people might add to their coffee could have an effect on heart rate, so if some people add milk/sugar and others don't (or if different people add different amounts of milk/sugar), then it could affect your results without having anything to do with the caffeine. This is related to why it's important for you to give everyone coffee, as opposed to giving some people coffee and others soda.

3. You are correct in how you've categorized your variables! But just keep in mind that if you decide to manipulate the amount of coffee/caffeine you give everyone, then you need to do that for every trial. So this means that each of your 3 trials needs to include a group of people drinking 2oz coffee, a second group drinking 4oz, and a third group drinking 8oz, and each person should be in the same group (drink the same amount of coffee) for each trial.

Another factor you might want to consider is how long after subjects consume the coffee you plan to wait before measuring their heart rates. I don't know how long it might take for caffeine to affect heart rate, but it's probably not going to be immediate, since it will take time for caffeine in the stomach to be absorbed into the bloodstream and possibly have an effect. You can probably do a simple google search for some guidance on how long to wait (unless your experiment already includes instructions on this).

4. This is a very good point to bring up. Yes, you will probably get the best results if your subjects don't eat or drink for some time before you give them their coffee, since having something in their stomachs may affect how quickly the caffeine from the coffee gets absorbed into their bodies to affect heart rate (as mentioned above).

I hope this clarifies a few things, and let me know if you still need a little help!

lkteja
Posts: 8
Joined: Sat Apr 01, 2017 10:06 am
Occupation: Student

### consent form when conducting experiment on test subjects or adult volunteers

Hi,

where will I find a consent form to get signed by adult volunteers giving me permission to perform a safe test like drinking coffee?

thanks

dcnick96
Moderator
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Joined: Wed Jul 25, 2007 7:59 pm

### Re: effect of caffeine on heart rate

Hello. This sounds like an interesting project! You can find more information about rules regarding human subjects here. There is a link on the right side for the actual forms.
https://student.societyforscience.org/human-participants

Also, we merged this question with your previous questions. Please keep all questions on the same thread so that our experts can best help you based on what has already been discussed.

Good luck!
Deana

Randel
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Joined: Wed May 30, 2018 4:46 am
Occupation: Teacher

### Re: effect of caffeine on heart rate

dcnick96 wrote:Hello. This sounds like an interesting project! You can find more information about rules regarding human subjects here. There is a link on the right side for the actual forms.
https://student.societyforscience.org/humancascodes/participants

Also, we merged this question with your previous questions. Please keep all questions on the same thread so that our experts can best help you based on what has already been discussed.

Good luck!

Good Comment, thanks for the help! Caffeine will only take you so far. it blocks phosphodiesterase, which leads to higher levels of epinephrine in circulation (LONG story, very simplified version) which is why you see effects like increased heart rate and vasodilation, among others. the thing is, if you are just looking to burn calories then 80% HR is going to burn the same amount no matter how you get there. taking longer to get there will probably result in a higher burn amount, but in the end, if you truly are hovering at 80% HR at the same activity level you are gonna be burning cal's at the same rate as w/out caffeine.

if your goal is to increase your overall cardiovascular fitness, that is a completely different story. that involves upregulation of blood cells, an adaptation of muscular tissue to the type of exercise, etc. that's going to require you to practice what you are training for. so if you want to run a 10k, you gotta practice running to facilitate that adaptation

my 2c anyway