

3.7 based on 145 ratings

Updated on Jul 16, 2013




What effect does caffeine have on human heart rate?


  • Mp3 player loaded with relaxing music
  • Eye mask
  • 5 cans of a caffeinated version of a drink
  • Paper and tape
  • Notebook



Taking Pulse Instructions

  9. Graph the data you recorded.


The results you get will depend strongly on what subjects you used for your study.


Caffeine is a stimulant, a class of drugs that increase your heart rate and make you more energetic. However, the effects of caffeine are not identical between subjects. Plenty of people are born with a natural tolerance to caffeine, meaning that the caffeine’s effects aren’t so pronounced when such people consume it. People without a natural tolerance may also develop one over time simply by drinking caffeine.

The possibility that certain people may have a tolerance to caffeine while others may not is one example of a variable—something that has a direct influence on the information we gather. Here’s an example of how this variable might work: you may find yourself testing two people that just happen to be naturally very tolerant to caffeine. If these happened to be the only two people you tested, you may not have seen a significant change in heart rate. This data may have led you to a misleading conclusion about caffeine’s effect on the human body! This is why you were instructed to test as many subjects as possible and why you were told to ask your subjects about their caffeine habits. When you take these steps, you can collect more useful data that lets you control the variable of tolerance by identifying the people that are more likely to have a similar tolerance to the drug.


1. This effect applies to the researchers, too. If researchers know they’re administering a drug as opposed to a placebo, there’s a chance they may look extra carefully for signs that the drug is doing something. This introduces bias into the experiment and can distort the results! A Double-Blind Study is one in which even the people administering the test don’t know what option they’re testing. This helps prevent bias from affecting the study’s results.